Patent Publication Number: US-2023133230-A1

Title: Sustained Release Aminopyridine Composition

Description:
CROSS REFERENCES 
     This application relates to U.S. Provisional Application Ser. No. 60/528,760, filed Dec. 11, 2003, U.S. Provisional Application No. 60/560,894 filed Apr. 9, 2004, U.S. Provisional Application No. 60/528,592 filed Dec. 11, 2003, 60/528,593 filed Dec. 11, 2003, and PCT/US2004/008101 filed on Mar. 17, 2004, all of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND 
     This invention relates to a sustained release oral dosage form of an aminopyridine pharmaceutical composition that can be used to treat individuals affected with neurological disorders wherein said pharmaceutical composition maximizes the therapeutic effect, while minimizing adverse side effects. 
     The sustained release oral dosage form of the present invention may be utilized to treat neurological disorders such as spinal cord injuries, multiple sclerosis, Alzheimer&#39;s disease, and ALS. Spinal cord injuries are one of the leading causes of disability in young adults resulting in from partial to complete paralysis of the lower extremities to partial to complete paralysis from the level of spinal injury downward. In the most extreme cases, paralysis is complete from the C-1 cervical vertebra downward. Oftentimes, however, the injury to the spinal cord does not consist of an actual severing of the cord but rather consists of an injury that interferes with signal transmission. Treatment alternatives for promoting transmission along injured nerves of the spinal cord have thus far met with limited success. 
     Multiple sclerosis (MS) is a degenerative and inflammatory neurological disease which affects the central nervous system, more specifically the myelin sheath. The condition of MS involves demyelination of nerve fibers resulting in short-circuiting of nerve impulses and thus a slowing or blocking of transmission along the nerve fibers, with associated disabling symptoms. Treatment alternatives for promoting transmission along affected nerves have thus far been limited. 
     Alzheimer&#39;s disease is a major cause of dementia in the elderly. It may be described as a progressive pathological deterioration in personality, memory and intellect consistent with a generalized atrophy of corresponding brain centers. The emotional state, behavior, cognitive function and thought processes of sufferers are all adversely affected. A minor degrading in memory which gradually becomes more apparent is the first indication of the onset of the disease. Part of the disease process involves the transmission of nerve signals and, as with MS, treatment alternatives have thus far been limited. 
     Amyotrophic lateral sclerosis (ALS), commonly referred to as Lou Gehrig&#39;s Disease, is a fatal neuromuscular disease characterized by progressive muscle weakness resulting in paralysis. ALS patients often suffer from symptoms including tripping, stumbling, and falling, loss of muscle control and strength in hands and arms, difficulty speaking, swallowing and/or breathing, chronic fatigue, and muscle twitching and/or cramping. ALS is characterized by both upper and lower motor neuron damage. Symptoms of upper motor neuron damage include stiffness, spasticity, muscle twitching (fasciculations), and muscle shaking (clonus). Symptoms of lower motor neuron damage include muscle weakness and muscle atrophy. 
     Potassium channel blockers are a class of compounds that have been found to improve the conduction of nerve impulses. As a result, they have become the focus of attention in the symptomatic treatment of spinal cord injury, MS and Alzheimer&#39;s disease. One sub-class of potassium channel blockers, aminopyridines have shown promise in the treatment of neurological diseases, 4-aminopyridine (4-AP), a mono-aminopyridine known as fampridine, has been found to slow the potassium flow in nerve impulse transmission and, thereby, shows effectiveness in restoring conduction in blocked and demyelinated nerves. 
     Potassium channel blockers have also been found to improve mental function in patients with Alzheimer&#39;s disease. This effect is believed to be related to the potassium channel blocking action which in turn enhances calcium influx into the neuron thus prolonging nerve action potential and increasing transmitter release. Mono- and di-aminopyridines constitute a particular sub-class of potassium channel blockers that have showed promise in the treatment of Alzheimer&#39;s disease. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a pharmaceutical composition which contains one or more potassium channel blockers and which can be used in the effective treatment of various diseases, for example, spinal cord injury, multiple sclerosis, Alzheimer&#39;s disease, and ALS. Embodiments of the present invention are directed to compositions that include a matrix and a potassium channel blocker. The potassium channel blockers may include aminopyridines, for example, 4-aminopyridine, 3,4-diaminopyridine and the like. The composition provides for sustained-release of the aminopyridine from the matrix to maintain the efficacious and safe plasma level of an aminopyridine. The aminopyridine dispersed in the matrix is capable of providing, upon administration to a patient, a desired release profile. The composition may be used to establish in patients in need of such treatment, a therapeutically effective blood plasma level of the aminopyridine for a period of at least about 6 hours and preferably up to at least 24 hours in the patient in a twice-daily administration while avoiding peaks and troughs in the relapse of the aminopyridine. The composition may include a mono- or di-aminopyridine, preferably 4-AP or 3,4-DAP or a combination thereof, homogeneously dispersed in a rate-controlling polymer matrix, preferably including a hydrophilic polymer like hydroxypropylmethylcellulose (HPMC). The composition of the present invention may also include one or more additional active ingredients and/or one or more pharmaceutically acceptable excipients. These compositions can be used to treat various neurological diseases, for example, spinal cord injury, multiple sclerosis, Alzheimer&#39;s disease, and ALS. 
     Another embodiment of the present invention is a stable pharmaceutical composition which comprises a therapeutically effective amount of an aminopyridine dispersed in a matrix that provides a release profile of the aminopyridine to a patient that has a desired C max  to C τ  ratio. The composition may be used to establish and/or maintain in a patient, a therapeutically effective level of the aminopyridine. Preferably the aminopyridine in the composition is released over time so that a therapeutically effective level of the aminopyridine in the patient can be achieved with twice daily dosing of the composition. In a more preferred embodiment, undesirable spikes or peaks in the release of the aminopyridine are avoided. 
     Another embodiment of the present invention is a stable, sustained-release oral dosage formulation of a composition which includes an a therapeutically effective amount of a 4-aminopyridine dispersed in a matrix that provides a release profile of 4-aminopyridine in the blood plasma of the patient extending over a period of at least 6 hours, preferably at least 8 hours, and more preferably, at least about 12 hours. In another embodiment, a stable, sustained-release oral dosage formulation of a composition includes an a therapeutically effective amount of a 4-aminopyridine dispersed in a matrix that provides a therapeutically effective blood plasma level of 4-aminopyridine in the patient extending over about 24 hours. 
     Preferably, the oral dosage formulation of the composition is a monolithic tablet formed by compression of the pharmaceutical composition of the present invention. In preferred embodiments, the oral dosage formulation includes a compressed tablet of a therapeutically effective amount of 4-aminopyridine dispersed in matrix which includes a hydrophilic polymer such as HPMC. The oral dosage form of the present invention may also include one or more pharmaceutically acceptable excipients. 
     The dispersion of 4-aminopyridine throughout the matrix imparts chemical and physical stability to the composition while providing a sustained-release profile. This enhanced dosage stability is most notably observed in compositions and dosage forms of the present invention having low concentrations of 4-aminopyridine, and stability is achieved while maintaining the desired controlled-release profile. Specifically, the compressed tablet formulation of the present invention exhibits superior resistance to moisture absorption by ambient humidity and maintains a uniform distribution of the 4-aminopyridine throughout the tablet while providing a release profile of 4-aminopyridine that permits establishment of a therapeutically effective concentration of the potassium channel blocker with once daily or twice daily dosing of the formulation. Preferably the therapeutically effective concentration released by the formulation extends over at least 6 hours, preferably at least 8 hours, and more preferably to at least 12 hours. In addition, the homogeneity of the dosage form renders it amenable to formation by simple and inexpensive manufacturing processes as compared with the multi-layered structure of prior sustained-release dosage formulations. 
     The compositions of the present invention may be used in the treatment of a condition in a patient which includes establishing a therapeutically effective concentration of a potassium channel blocker in the patient in need thereof. The compositions may be used for building up a level and or maintaining a therapeutically effective concentration of an aminopyridine in the patient by twice daily dosing. The dosages of the present compositions can made with a lower concentration of the aminopyridine to facilitate restful periods for the patient during the day. Where desirable, the compositions of the present invention may be formulated to avoid large peaks in initial release of the aminopyridine. The compositions of the present invention when administered to a patient in need thereof provide for the treatment of neurological diseases that are characterized by a degradation of nerve impulse transmission. Preferably, the compositions are a stable, sustained-release tablet of a therapeutically effective amount of a mono- or di-aminopyridine, dispersed in HPMC such that therapeutically effective blood plasma level of the mono- or di-aminopyridine is maintained in the patient for a period of at least 6 hours, preferably at least 8 hours, and more preferably at least about 10-12 hours in a once or twice daily administration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a graph of mean plasma profiles associated with the administration to a patient in both fasted and fed states of a tablet form of 4-AP (fampridine) in accordance with the present invention compared with the mean plasma profile associated with the administration of an immediate release formulation of 4-AP n a gelatin capsule. 
         FIG.  2    is a graph of mean plasma profiles associated with the administration (fasted state) of a homogeneous dispersion of 4-AP (fampridine) in a matrix in a tablet form of in accordance with the present invention compared with the mean plasma profile associated with the administration of a layered controlled-release capsule and an immediate release capsule formulations of 4-AP. 
         FIG.  3    is a graph of the mean change in walking sped observed with the administration of a sustained release 4-AP (fampridine) according to the present invention. 
         FIG.  4    is a graph of the mean change in LEMMT with the administration of a sustained release 4-AP (fampridine) according to the present invention. 
         FIG.  5    is a graph of the mean change in Ashworth score with the administration of a sustained release 4-AP (fampridine) according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Before the present compositions and methods are described, it is to be understood that this invention is not limited to the particular molecules, compositions, methodologies or protocols described, as these may vary. It is also to be understood that the terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope of the present invention which will be limited only by the appended claims. 
     The terms used herein have meanings recognized and known to those of skill in the art, however, for convenience and completeness, particular terms and their meanings are set forth below. 
     It must also be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include plural reference unless the context clearly dictates otherwise. Thus, for example, reference to a “spheroid” is a reference to one or more spheroid and equivalents thereof known to those skilled in the art, and so forth. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of embodiments of the present invention, the preferred methods, devices, and materials are now described. All publications mentioned herein are incorporated by reference. Nothing herein is to be construed as an admission that the invention is not entitled to antedate such disclosure by virtue of prior invention. 
     “Buccal” refers to the cheek area in the mouth. 
     “Local administration” means direct administration by a non-systemic route at or in the vicinity of the site of affliction, disorder, or perceived pain. 
     The terms “patient” and “subject” mean all animals including humans. Examples of patients or subjects include humans, cows, dogs, cats, goats, sheep, and pigs. 
     The term “pharmaceutically acceptable salts, esters, amides, and prodrugs” as used herein refers to those carboxylate salts, amino acid addition salts, esters, amides, and prodrugs of the compounds of the present invention which are, within the scope of sound medical judgment, suitable for use in contact with the tissues of patients without undue toxicity, irritation, allergic response, and the like, commensurate with a reasonable benefit/risk ratio, and effective for their intended use, as well as the zwitterionic forms, where possible, of the compounds of the invention. 
     The term “prodrug” refers to compounds that are rapidly transformed in vivo to yield the parent compounds of the above formula, for example, by hydrolysis in blood. A thorough discussion is provided in T. Higuchi and V. Stella, “Pro-drugs as Novel Delivery Systems,” Vol. 14 of the A.C.S. Symposium Series, and in Bioreversible Carriers in Drug Design, ad. Edward B. Roche, American Pharmaceutical Association and Pergamon Press, 1987, both of which are incorporated herein by reference. 
     The term “alts” refers to the relatively non-toxic, inorganic and organic acid addition salts of compounds of the present invention. These salts can be prepared in situ during the final isolation and purification of the compounds or by separately reacting the purified compound in its free base form with a suitable organic or inorganic acid and Isolating the salt thus formed. Representative salts include the hydrobromide, hydrochloride, sulfate, bisulfate, nitrate, acetate, oxalate, valerate, oleate, palmitate, stearate, laurate, borate, benzoate, lactate, phosphate, tosylate, citrate, maleate, fumarate, succinate, tartrate, naphthylate mesylate, glucoheptonate, lactobionate and laurylsulphonate salts, and the like. These may include cations based on the alkali and alkaline earth metals, such as sodium, lithium, potassium, calcium, magnesium, and the like, as well as non-toxic ammonium, tetramethylammonium, tetramethylammonium, methlyamine, dimethlyamine, trimethlyamine, triethlyamine, ethylamine, and the like. (See, for example, S. M. Barge et al., “Pharmaceutical Salts,” J. Pharm. Sci., 1977, 66:1-19 which is incorporated herein by reference.). 
     “Slow or sustained release formulation” refers to a formulation designed to release a therapeutically effective amount of drug or other active agent such as a polypeptide or a synthetic compound over an extended period of time, with the result being a reduction in the number of treatments necessary to achieve the desired therapeutic effect. In the matter of the present invention, a slow release formulation would decrease the number of treatments necessary to achieve the desired effect in terms of reduction in pain or spasticity, or an improvement in motor or sensory function in patients in need of such therapy, for example, in spinal cord injured patients or in patients suffering from multiple sclerosis. ALS or Alzheimer&#39;s disease. The slow or sustained release formulations of the present invention achieve a desired pharmacokinetic profile in a subject. 
     “Sublingual delivery” refers to the system delivery of drugs or other agents through the mucosal membranes lining the floor of the mouth. 
     A “therapeutically effective amount” is an amount sufficient to decrease or prevent the symptoms associated with a medical condition or infirmity or to normalize body functions in disease or disorders that result in impairment of specific bodily functions. As related to the present application, a therapeutically effective amount is an amount sufficient to reduce the pain or spasticity associated with the neurological disorder being treated, or an amount sufficient to result in improvement of sexual, bladder or bowel function in subjects having a neurological disorder which impairs nerve conduction, which hinders normal sexual, bladder or bowl functions. 
     “Treatment” refers to the administration of medicine or the performance of medical procedures with respect to a patient, for either prophylaxis (prevention) or to cure the infirmity or malady in the instance where the patient is afflicted. 
     In addition, the compounds of the present invention can exist in unsolvated as well as solvated forms with pharmaceutically acceptable solvents such as water, ethanol, and the like. In general, the solvated forms are considered equivalent to the unsolvated forms for the purposes of the present invention. 
     One aspect of the invention is a sustained-release pharmaceutical composition comprising an aminopyridine dispersed in a sustained release matrix such as a rate-controlling polymer. The composition of the present invention is capable of providing, upon administration to a patient, a release profile of the aminopyridine extending over at least 6 hours, preferably least about 12 hours, and more preferably at least 24 hours or more Preferably the aminopyridine concentration in the composition is a therapeutically effective amount, and preferably the aminopyridine is dispersed uniformly throughout the release matrix. A therapeutically effective amount is an amount of a potassium channel blocker, preferably an aminopyridine compound, that when administered to a patient or subject, ameliorates a symptom of a neurological disease. 
     When the compositions of the present invention are administered to a patient, the concentration of the aminopyridine in the patient&#39;s plasma over time (release profile) may extend over a period of at least 6 hours, preferably over at least 8 hours, and more preferably over at about 12 hours. The compositions may provide in single dose a mean maximum plasma concentration of aminopyridine in the patient of from about 15 to about 180 ng/ml; a mean T max  from about 1 to about 6 hours, more preferably about 2 to about 5.2 hours after administration of the composition to the patient. 
     In one embodiment, aminopyridine is administered to a subject at a dose and for a period sufficient to allow said subject to tolerate said dose without showing any adverse effects and thereafter increasing the dose at selected intervals of time until a therapeutic dose is achieved. In one embodiment the medicament is administered to a subject at a dose and for a period sufficient to allow said subject to tolerate said dose without showing any adverse effects and thereafter increasing the dose of aminopyridine at selected intervals of time until a therapeutic dose is achieved. For example, at the commencement of treatment aminopyridine is preferably administered at a dose less than 15 mg/day until a tolerable state is reached. Suitably when said tolerable state is reached, the dose administered may be increased by amounts of at least 5-15 mg/day until said therapeutic dose is reached. The method can include scheduling administration of doses of the pharmaceutical so that the concentration of the aminopyridine in the patient is at about the minimum therapeutically effective level to ameliorate the neurological condition, yet relatively lower compared to the maximum concentration in order to enhance restful periods for the patient during the day. Preferably the method provides for the treatment of neurological diseases characterized by a degradation of nerve impulse transmission comprising the step of administering to a patient a composition of the present invention. 
     The formulations and compositions of the present invention exhibit a specific, desired release profile which maximizes the therapeutic effect while minimizing adverse side effects. The desired release profile may be described in terms of the maximum plasma concentration of the drug or active agent (C max ) and the plasma concentration of the drug or active agent at a specific dosing interval (Cτ). A ratio of C max  to C τ  (C max :C τ ) may be calculated from the observed C max  and C τ . A dosing interval (τ) is the time since the last administration of the drug or active agent. In the present application, the dosing interval (τ) is twelve (12) hours, therefore C τ  is the concentration of the drug or active agent at twelve (12) hours from the last administration. 
     Additionally, the formulations and compositions of the present invention exhibit a desired release profile that may be described in terms of the maximum plasma concentration of the drug or active agent at steady state (C maxSS ) and the minimum plasma concentration of the drug or active agent at steady state (C minSS ). Steady state is observed when the rate of administration (absorption) is equal to the rate of elimination of the drug or active agent. A ratio of C maxSS  to C minSS  (C maxSS :C minSS ) may be calculated from the observed C maxSS  and C minSS . In addition, the formulations and compositions of the present invention exhibit a desired release profile that may be described in terms of the average maximum plasma concentration of the drug or active agent at steady state (C avSS ). 
     Another embodiment is a sustained release tablet of a sustained release matrix and an aminopyridine, said tablet exhibits a release profile to obtain a C max :C τ  ratio in vivo of 1.0 to 3.5, and more preferably a C max :C τ  ratio of about 1.5 to about 3.0. In another preferred embodiment, the C max :C τ  ratio is about 2.0 to about 3.0. The aminopyridine may comprise 4-aminopyridine. The sustained release matrix may include for example, hydroxypropylmethylcellulose, or other rate controlling matrices that are suitable for controlling the release rate of an aminopyridine for use in the pharmaceutical compositions of the present invention. 
     In a further embodiment, a sustained release tablet of a sustained release matrix and an aminopyridine, wherein the tablet exhibits an in vivo C max :C τ  ratio of about 2.0 to about 3.0. 
     A method of treating a disease associated with a neurological disorder is also provided. The method may include administering an 4-aminopyridine on a dosing regimen to obtain an in vivo C max :C τ  ratio of 1.0 to 3.5. In more preferred embodiments, the C max :C τ  ratio is about 1.5 to 3.0, and about 2.0 to about 3.0. Such neurological disorders include a spinal cord injury, Alzheimer&#39;s disease, multiple sclerosis, ALS or the like. The dosing regimen of the method of treating a neurological disorder may comprise administering a tablet of said aminopyridine twice daily dosing. In a further embodiment, the twice-daily dosing regiment of the aminopyridine may comprise every twelve hours. 
     Another embodiment is a method of treating a neurological disorder comprising administering an aminopyridine to achieve an in vivo C max :C τ  ratio of 1.0 to 3.5, and more preferably the C max :C τ  ratio is about 1.5 to about 3.25. In another preferred embodiment, the C max :C τ  ratio of the method of treating a neurological disorder is about 2.0 to about 3.0. 
     Another aspect is a therapeutic composition of a release matrix and an active aminopyridine, wherein the aminopyridine is released from the release matrix at a rate to maintain a C max :C τ  ratio of 1.0 to 3.5, and more preferably about 1.5 to about 3.0. In another preferred embodiment, the C max :C τ  ratio of the therapeutic composition is about 2.0 to about 3.0. 
     Another embodiment is a sustained release tablet of a sustained release matrix and an aminopyridine, said tablet exhibits a release profile to obtain a C max :C τ  ratio in vivo of 1.0 to 3.5 and a C avSS  of about 15 ng/mi to about 35 ng/ml, and more preferably a C max :C τ  ratio of about 1.5 to about 3.0. In another preferred embodiment, the C max :C τ  ratio is about 2.0 to about 3.0. 
     In another embodiment, a sustained release tablet comprising a sustained release matrix and an aminopyridine, said tablet exhibiting an in vivo C max :C τ  ratio of about 2.0 to about 3.0 and a C avSS  of about 15 ng/ml to about 35 ng/ml is provided. 
     A further embodiment is a method of treating a disease associated with a neurological disorder, said method comprising administering an aminopyridine on a dosing regimen to obtain an in vivo C max :C τ  ratio of 1.0 to 3.5 and a C avSS  of about 15 ng/ml to about 35 ng/ml. 
     A further aspect is a method of treating a disease associated with a neurological disorder comprising administering an aminopyridine to achieve an in vivo C max :C τ  ratio of 1.0 to 3.5 and a C avSS  of about 15 ng/ml to about 35 ng/ml. 
     In a further aspect, a therapeutic composition comprised of a release matrix and an active aminopyridine, said aminopyridine being released from said release matrix at a rate to maintain an in vivo C max :C τ  ratio of 1.0 to 3.5 and a C avSS  of about 15 ng/ml to about 35 ng/ml is provided. 
     In another embodiment, a method of treating a disease associated with a neurological disorder, said method comprising administering an aminopyridine on a dosing regimen to obtain an in vivo C maxSS :C minSS  ratio of 1.0 to 3.5 and a C avss  of about 15 ng/ml to about 35 ng/ml is provided. 
     A further aspect is a sustained release composition comprising a sustained release matrix and an aminopyridine, wherein said composition provides a C avss  of about 15 ng/ml to about 35 ng/ml. In a further aspect, a sustained release tablet comprising a sustained release matrix and an aminopyridine, said tablet exhibiting a C maxss  of about 20 ng/ml to about 35 ng/ml is provided. 
     In another embodiment, a sustained release tablet comprising a sustained release matrix and an aminopyridine, said tablet exhibiting a C maxss  of about 30 ng/ml to about 55 ng/ml. In a further embodiment, a sustained release tablet comprising a sustained release matrix and an aminopyridine, said tablet exhibiting a C maxss  of about 24 ng/ml to about 40 ng/ml is provided. In a further embodiment, a sustained release tablet comprising sustained release matrix and an aminopyridine, said tablet exhibiting a C maxss  of about 35 ng/ml to about 55 ng/ml is provided. 
     A further aspect is a method of treating a disease associated with a neurological disorder comprising administering an aminopyridine on a dosing regimen in vivo C maxSS :C minSS  ratio of 1.0 to 3.5, preferably an in vivo C maxSS :C minSS  ratio of about 1.5 to about 3.0, and more preferably about 2.0 to about 3.0. The dosing regimen may consist of administering the aminopyridine twice daily, more preferably every twelve hours. 
     The amount of a pharmaceutically acceptable quality aminopyridine, salt, solvated, or prodrug thereof included in the pharmaceutical composition of the present invention will vary, depending upon a variety of factors, including, for example, the specific potassium channel blocker used, the desired dosage level, the type and amount of rate-controlling polymer matrix used, and the presence, types and amounts of additional materials included in the composition. Preferably, the aminopyridine comprises from about 0.1 to about 13% w/w, more preferably from about 0.5 to about 6.25% w/w. In an even more preferable embodiment of the present invention the aminopyridine is present from about 0.5 to 4.75% w/w of the pharmaceutical composition. It has been found that for many indications a weight (wt/wt %) above about 5% can result in undesirable side effects. Accordingly, a weight percentage less than about 4.75% is desired. The amount of aminopyridine, or a derivative thereof, in the formulation varies depending on the desired dose for efficient drug delivery, the molecular weight, and the activity of the compound. The actual amount of the used drug can depend on the patient&#39;s age, weight, sex, medical condition, disease or any other medical criteria. The actual drug amount is determined according to intended medical use by techniques known in the art. The pharmaceutical dosage formulated according to the invention may be administered once or more times per day, preferably two or fewer times per day as determined by the attending physician. 
     Typically, the 4-aminopyridine is formulated in tablets or other pharmaceutical composition in amounts of about 0.5 mg to about 80 mg, preferably from about 5 to about 50 mg of 4-aminopyridine. Preferably, the amount of an aminopyridine in the composition is formulated to maintain therapeutic levels of the aminopyridine in patient&#39;s blood up to about 80 ng/ml. 
     The matrix in which the aminopyridine is homogeneously dispersed provides a sustained release of the aminopyridine into the plasma of the patient. Polymeric matrices suitable for controlling the release rate of aminopyridines for use in the pharmaceutical compositions of the present invention include hydrophilic polymers, hydrophobic polymers or mixtures of hydrophilic and/or hydrophobic polymers that are capable of forming sustained-release dosage formulation in combination with an aminopyridine. Such matrices are also capable of preventing degradation and loss of the aminopyridine from the composition. Examples of suitable matrices either alone or in combination include but are not limited to hydroxyalkylcelluloses, such as hydroxypropylcellulose and HPMC, hydroxyethyl cellulose, alkylcelluloses such as ethycellulose and methylcellulose, carboxymethylcellulose; sodium carboxymethylcellulose, hydrophilic cellulose derivatives, polyethylene oxide, polyethylene glycol, polyvinylpyrrolidone; cellulose acetate, cellulose acetate butyrate, cellulose acetate phthalate, cellulose acetate trimellitate, polyvinylacetate phthalate, hydroxypropylmethyl-cellulose phthalate, hydroxypropylmethyl-cellulose acetate succinate; poly(alkyl methacrylate); and poly(vinyl acetate). Examples of other suitable polymers include, either alone or in combination, carboxyvinylpolymers, poly(vinyl alcohols), glucans, scleroglucans, mannans, xanthans, and, in general, cellulose, crosslinked polyvinylpyrrolidone, carboxymethyl starch, potassium methacrylate-divinylbenzene copolymer, hydroxypropylcyclodextrin, alpha, beta, gamma cyclodextuin or derivatives and other dextran derivatives, natural gums, seaweed extract, plant exudate, agar, agarose, algin, sodium alginate, potassium alginate, carrageenan, kappa-carrageenan, lambda-carrageenan, fucoidan, furcellaran, laminarin, hypnea, eucheuma, gum arabic, gum ghatii, gum karaya, gum tragacanth, guar gum, locust bean gum, okra gum, quince psyllium, flax seed, arabinogalactin, pectin, scleroglucan, dextran, amylose, amylopectin, dextrin, acacia, karaya, guar, a swellable mixture of agar and carboxymethyl cellulose, a swellable composition comprising methyl cellulose mixed with a sparingly cross-linked agar, a blend of sodium alginate and locust bean gum polymers or copolymers derived from acrylic or methacrylic acid esters, copolymers of acrylic and methacrylic acid esters, zein, waxes, shellac and hydrogenated vegetable oils. 
     In certain embodiments, the matrix is a rate-controlling polymer such as but not limited to HPMC. HPMC is a hydroxyalkylcellulose characterized by a polymeric backbone of cellulose, a natural carbohydrate that contains a basic repeating structure of anhydroglucose units, and varying ratios of hydroxypropyl and methyl substitution at the three available substitution positions. The amount of substituent groups on the anhydroglucose units can be designated by weight percent or by the average number of substituent groups attached to the ring. For example, if all three available positions on each unit are substituted, the degree of substitution may be designated as 3 whereas if an average of two positions on each ring am reacted, the degree of substitution is correspondingly designated as 2. 
     According to one method of manufacture, cellulose fibers are heated with a caustic solution and then treated with methyl chloride and propylene oxide to produce HPMC. The fibrous reaction product is purified and ground to a fine, uniform powder. Especially suitable HPMCs manufactured according to this process are sold under the Methocel K designation, such as Methocel K100LV, Methocel K15M, Methocel K4M and Methocel K100M, all available from the Dow Chemical Co. Methocel K products are generally characterized by a methoxyl degree of substitution of about 1.4, a methoxyl percentage of about 22%, a hydroxypropyl molar substitution of about 0.2, a hydroxypropyl percentage of about 8%, and a particle size of 90%&lt;100 mesh. In a preferred embodiment, the rate-controlling polymer is HPMC sold under the name Methocel K100LV. 
     Interaction between the matrix, excipients or other additives and the potassium channel blocker through van der Waal forces, hydrogen bonding, coordination, solvation, or complex formation may also be desirable to control the release of the potassium channel blocker from the composition and to prevent evaporation and or degradation of the potassium channel blocker within the composition. 
     In preferred embodiments, the raw-controlling polymer is HPMC. In such embodiments, the HPMC preferably has a viscosity (2 wt % solution at 20° C.) of about 100 to 100,000 cps, more preferably 100 to 30,000 cps. Especially suitable HPMCs are Methocel K types, such as Methocel K100LV, Methocel K15M, Methocel K4M and Methocel K100M, available from the Dow Chemical Co. The hydroxypropylmethylcelluloses used according to the invention preferably have a molecular weight of about 80,000 to about 1,150,000, more preferably about 80,000 to about 600,000. Especially suitable is a hydroxypropylmethylcellulose sold under the name Klucel LF available from Aqualon and Nippon Soda Co., which has a molecular weight of 100,000. The poly(ethylene oxide) used according to the invention preferably has a molecular weight of about 100,000 to about 7,000,000, more preferably about 900,000 to about 7,000,000. An especially suitable poly(ethylene oxide) is sold under the name Polyox WSR Coagulant available from the Dow Chemical Co., which has a molecular weight of 5,000,000. The ethylcelluloses used according to the invention preferably have a viscosity of about 3 to about 110 cps, more preferably about 7 to about 100 cps. In particularly preferred embodiments, the rate-controlling polymer is the HPMC sold under the name Methocel K100LV. 
     In another embodiment, the rate-controlling polymer is HPC. HPCs used according to the invention preferably have a viscosity (2 wt % solution at 20° C.) of about 10 to 100,000 cps, more preferably 100 to 30,000 cps, and a molecular weight of about 80,000 to about 1,150,000, more preferably about 80,000 to about 600,000. An especially suitable HPC is sold under the name Klucel LF available from Aqualon and Nippon Soda Co. which has a molecular weight of about 95,000. 
     In another embodiment, the rate-controlling polymer release matrix is poly(ethylene oxide) preferably having a molecular weight of about 100,000 to about 7,000,000, more preferably about 900,000 to about 7,000,000. An especially suitable poly(ethylene oxide) is sold under the name Polyox WSR Coagulant available from the Dow Chemical Co. which has a molecular weight of about 5,000,000. Suitable ethylcelluloses that may be used as the rate-controlling polymer in accordance with the invention preferably have a viscosity of about 3 to about 110 cps, more preferably about 7 to about 100 cps. 
     The polymeric matrix of the drug delivery of the invention may additionally also contain a hydrophobic polymer. Suitable hydrophobic polymers are hydrophobic cellulose derivatives, such as ethyl cellulose, fats, such as glycerol palmitostearate, waxes, such as beeswax, glycowax, castrowax, carnaubawax, glycerol monostearate or stearylalcohol, hydrophobic polyacriamide derivatives and hydrophobic methacrylic acid derivatives. 
     A hydrophobic polymer may be included as part of a release matrix, in order to modify the release kinetics. Preferably such a hydrophobic polymer is used only in a mixture of hydrophilic and hydrophobic polymers. In such a mixture, the hydrophobic polymer controls the water penetration rate into the delivery system. For example, incorporation of a hydrophobic polymer into the polymer matrix and the ratio of hydrophilic to hydrophobic polymer thus changes the erosion characteristics of the tablet. The hydrophobic polymer shows down the water penetration into the tablet and thus slows the tablet erosion. 
     The amount of the release matrix included in the pharmaceutical composition of the present invention will vary depending upon a variety of factors, including, for example, the specific matrix used, its molecular weight, is hydrophilicity, the type and amount of potassium channel blocker used, and the presence, types and amounts of additional materials included in the composition. Preferably, the rate-controlling polymer comprises from about 20 to about 96% w/w, more preferably from about 20 to about 70% w/w, of the pharmaceutical composition. It is desirable that the matrix permit release of the potassium channel blocker in the lower gastrointestinal tract. 
     In general, when the viscosity grade of the matrix polymer is higher, the release rate of the drug is slower. The size, shape and surface area of the tablet may also be modified to increase or decrease the release rate of the aminopyridine from the tablet. 
     In preferred embodiments, the aminopyridine is milled prior to dispersal in the rate-controlling polymer in order to ensure proper particle size distribution. Milling of the aminopyridine may be accomplished by any suitable means such as, for example, an air jet mill, a micronizer, a hammer mill, a ball mill, a cone mill, or other suitable type of mill. The milling is preferably accomplished so that the particle size distributions permit satisfactory dosage content uniformity and dissolution profiles. The particle size distribution may be ±25% of the mean particle size use in the formulation. In a preferred embodiment, the aminopyridine is milled so that 90% of the particles are smaller than about 1.3 mm, more preferably smaller than about 1 mm, and even more preferably smaller than about 300 μm; 50% of the particles are smaller than about 1 mm, more preferably smaller than about 600 μm, and even more preferably smaller than about 150 μm; and 10% of the particles are smaller than about 500 μm, more preferably smaller than about 400 μm, and even more preferably smaller than about 50 μm. 
     Suitable screen sizes are from about #10 to about #400 mesh, preferably #24 to #60 mesh. In certain embodiments, milling of the aminopyridine may involve multiple passes of the material through mesh screens at the same or different mill blade orientations. In one embodiment, the milling process involves two passes of 4-AP through a #24 mesh screen in a FitzMil® comminutor using two different mill blade orientations. 
     The aminopyridine, in either milled or un-milled form, is dispersed in the release matrix to form the pharmaceutical composition such that the aminopyridine is distributed substantially uniformly throughout the entirety of the matrix. The dispersal of aminopyridine throughout the matrix may be accomplished by any method capable of achieving substantial homogeneity. Preferred dispersal methods include the use of blenders, for example, planetary and cross-flow blenders. While blending time will vary depending on a variety of factors, including, for example, the specifics of the aminopyridine and rate-controlling polymer used, substantially uniform distribution is preferably realized within from about 10 to about 55 minutes of blending. 
     The release matrix aminopyridine formulation is preferably fabricated into tablets, capsules or granules for oral use. The rate of aminopyridine release from the tablets may be controlled by the erosion mechanism of the release matrix from which aminopyridine is released. In general, for producing a tablet on an industrial scale, the drug and polymer are granulated alone or in combination. Preferably the release of the aminopyridine from the matrix of the pharmaceutical composition is relatively linear over time. Preferably the matrix provides a release profile that gives a therapeutically effective concentration of the aminopyridine in the plasma of the patient permitting a once per day or twice per day dosing. Preferably the sustained release aminopyridine formulation for oral administration to patients includes from about 0.0001 mole to about 0.0013 mole aminopyridine that provides a mean maximum plasma concentration of aminopyridine from about 15 to about 180 ng/ml, a mean T max  of about 2 to about 5 hours after administration, and a mean minimum plasma concentration of from about 10 to 60 ng/ml at about 8-24 hours after administration. 
     The formulations of the invention are prepared by procedures known in the art, such as, for example, by the dry or wet method. The method selected for manufacturing affects the release characteristics of the finished tablet. In one method, for example, the tablet is prepared by wet granulation in the presence of either water or an aqueous solution of the hydrophilic polymer or using other binder as a granulating fluid. In alternative, organic solvent, such as isopropyl alcohol, ethanol and the like, may be employed with or without water. The drug and polymer may be granulated alone or in combination. Another method for preparation of the tablet which may be used requires using a drug-polymer dispersion in organic solvents in the presence or absence of water. Where the aminopyridine or its derivative has very low solubility in water it may be advantageous to reduce the particle size, for example, by milling it into fine powder and in this way to control the release kinetics of the drug and enhance its solubility. 
     The hardness of the tablets of the present invention may vary, depending on a variety of factors, including, for example, the relative amounts and specific types of ingredients used, the tableting equipment employed, and the selected processing parameters. The pressure used to prepare the tablets can influence the release profile of the aminopyridine into the patient. The pressure used to prepare the tablets of the present invention may vary depending upon their surface area and the amount and particle size of aminopyridine, additive, excipients, or binders included in the tablet. The degree of hydration and solvation of the components in the composition will also be important in determining the hard ness of the tablets. Preferably the formed tablets have a hardness in the range of from 80-400 N, and more preferably from 150 to 300 N. 
     Pellets or a combination of pellets in accordance with the invention may also be filled into hard or soft gelatin capsules. The pellets included in the capsule may have different amounts of aminopyridine in the pellets and or different matrices. Various amounts of the pellets may be used to tailor the total amount aminopyridine delivered as well as to alter the release and concentration profile of the aminopyridine in the patient. 
     The effects of various matrices, concentrations of aminopyridine, as well as various excipients and additives to the composition on the concentration of the channel blocker on the dissolution rate may be monitored for example using a type H dissolution apparatus according to U.S. Pharmacopoeia XXII, or USP Apparatus II (Paddle Method). Clinical evaluations may be used to study the effects on plasma levels of various release matrices, concentrations of aminopyridine, as well as various excipients and additives. Plasma aminopyridine concentrations may be used to calculate pharmacokinetic data (release profiles) including apparent absorption and elimination rates, area-under-de curve (AUC), maximum plasma concentration (C max ), time to maximum plasma concentration (T max ), absorption half-life (T 1/2 (abs)), and elimination half-life (T 1/2 (elim)). Pharmacodynamic effects may be assessed based upon response tests, such as muscle strength improvement or reduction in spasticity for patients with multiple sclerosis or spinal cord injury or other tests as would be known to those skilled in the art. Plasma aminopyridine concentration in blood plasma or cerebral spinal fluid may be monitored using liquid chromatography/MS/MS assay methods. 
     The drug delivery of the invention can utilize any suitable dosage unit form. Specific examples of the delivery system of the invention are tablets, tablets which disintegrate into granules, capsules, sustained release microcapsules, spheroids, or any other means which allow for oral administration. These forms may optionally be coated with pharmaceutically acceptable coating which allows the tablet or capsule to disintegrates in various portions of the digestive system. For example a tablet may have an enteric coating which prevents it from dissolving until it reaches the more basic environment of the small intestine. 
     The dispersion of the aminopyridine throughout the release matrix imparts enhanced stability characteristics in the dosage formulation. This enhanced stability is achieved without loss of the desired sustained-release profile. Preferably the release profile, which may be measured by dissolution rate is linear or approximately linear, preferably the release profile is measured by the concentration of the aminopyridine in the plasma in the patient and is such to permit twice daily (BID) dosing. 
     The pharmaceutical composition of the present invention can include also auxiliary agents or excipients, for example, glidants, dissolution agents, surfactants, diluents, binders including low temperature melting binders, disintegrants and/or lubricants. Dissolution agents increase the dissolution rate of the aminopyridine from the dosage formulation and can function by increasing the solubility of the aminopyridine. Suitable dissolution agents include, for example, organic acids such as citric acid, fumaric acid, tartaric acid, succinic acid, ascorbic acid, acetic acid, malic acid, glutaric acid and adipic acid, and may be used alone or in combination. These agents may also be combined with salts of the acids, e.g. sodium citrate with citric acid, in order to produce a buffer system. 
     Other agents that may alter the pH of the microenvironment on dissolution and establishment of a therapeutically effective plasma concentration profile of the aminopyridine include salts of inorganic acids and magnesium hydroxide. Other agents that may be used are surfactants and other solubilizing materials. Surfactants that are suitable for use in the pharmaceutical composition of the present invention include, for example, sodium lauryl sulphate, polyethylene separates, polyethylene sorbitan fatty acid esters, polyoxyethylene castor oil derivatives, polyoxyethylene alkyl ethers, benzyl benzoate, cetrimide, cetyl alcohol, docusate sodium, glyceryl monooleate, glyceryl monostearate, glyceryl palmitostearate, lecithin, medium chain triglycerides, monoethanolamine, oleic acid, poloxamers, polyvinyl alcohol and sorbitan fatty acid esters. 
     Diluents that are suitable for use in the pharmaceutical composition of the present invention include, for example, pharmaceutically acceptable inert fillers such as microcrystalline cellulose, lactose, sucrose, fructose, glucose dextrose, or other sugars, dibasic calcium phosphate, calcium sulfate, cellulose, ethylcellulose, cellulose derivatives, kaolin, mannitol, lactitol, maltitol, xylitol, sorbitol, or other sugar alcohols, dry starch, saccharides, dextrin, maltodextrin or other polysaccharides, inositol or mixtures thereof. The diluent is preferably a water-soluble diluent. Examples of preferred diluents include, for example: microcrystalline cellulose such as Avicel PH112, Avicel PH101 and Avicel PH102 available from FMC Corporation; lactose such as lactose monohydrate, lactose anhydrous, and Pharmatose DCL 21; dibasic calcium phosphate such as Emcompress available from Penwest Pharmaceuticals; mannitol; starch; sorbitol; sucrose; and glucose. Diluents are carefully selected to match the specific composition with attention paid to the compression properties. The diluent is preferably used in an amount of about 10 to about 80% by weight, preferably about 20 to about 50% by weight, of the sustained-release composition. 
     Glidants are used to improve the flow and compressibility of ingredients during processing. Suitable glidants include, for example, colloidal silicon dioxide, a sub-micron fumed silica that can be prepared by, for example, vapor-phase hydrolysis of a silicon compound such as silicon tetrachloride. Colloidal silicon dioxide is a sub-micron amorphous powder which is commercially available from a number of sources, including Cabot Corporation (under the tradename Cab-O-Sil); Degussa, Inc. (under the tradename Aerosil); and E.I. DuPont &amp; Co. 
     Colloidal silicon dioxide is also known as colloidal silica, fumed silica, light anhydrous silicic acid, silicic anhydride, and silicon dioxide fumed, among others. In one embodiment, the glidant comprises Aerosil 200. 
     Another agent that may be used is a surfactant, dissolution agent and other solubilizing material. Surfactants that are suitable for use in the pharmaceutical composition of the present invention include, for example, sodium lauryl sulphate, polyethylene stearates, polyethylene sorbitan fatty acid esters, polyoxyethylene castor oil derivatives, polyoxyethylene alkyl ethers, benzyl benzoate, cetrimide, cetyl alcohol, docusate sodium, glyceryl monooleate, glyceryl monostearate, glyceryl palmitostearate, lecithin, medium chain triglycerides, monoethanolamine, oleic acid, poloxamers, polyvinyl alcohol and sorbitan fatty acid esters. 
     Dissolution agents increase the dissolution rate of the aminopyridine and function by increasing the solubility of the aminopyridine. Suitable dissolution agents include, for example, organic acids such as citric acid, fumaric acid, tartaric acid, succinic acid, ascorbic acid, acetic acid, malic acid, glutaric acid and adipic acid, which may be used alone or in combination. These agents may also be combined with salts of the acids, e.g. sodium citrate with citric acid, in order to produce a buffer system. Other agents that may be used to alter the pH of the microenvironment on dissolution include salts of inorganic acids and magnesium hydroxide. 
     The pellets or granulates may be compressed into tablets using a binder and/or hardening agent commonly employed in tablets such as microcrystalline cellulose sold under the Trade Mark “AVICEL” or a co-crystallized powder of highly modified dextrins (3% by weight) and sucrose sold under the Trade Mark “DI-PAC” in such a way that the specific dissolution rate of the pellets is maintained. Binders that are suitable for use in the pharmaceutical composition of the present invention include, for example, starches, ethyl cellulose, polyvinylpyrrolidone, acacia, guar gum, hydroxyethylcellulose, agar, calcium carrageenan, sodium alginate, gelatin, saccharides (including glucose, sucrose, dextrose and lactose), molasses, extract of Irish moss, panwar gum, ghatti gum, mucilage of isapol husk, carboxymethylcellulose, methylcellulose, veegum, larch arbolactan, polyethylene glycols, waxes and mixtures thereof. Suitable low temperature melting binders include, for example, polyethylene glycols such as PEG 6000, cetostearyl alcohol, cetyl alcohol, polyoxyethylene alkyl ethers, polyoxyethylene castor oil derivatives, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene stearates poloxamers, and waxes. 
     Disintegrants that are suitable for use in the pharmaceutical composition of the present invention include, for example, starches, sodium starch glycollate, crospovidone, croscarmellose, microcrystalline cellulose, low substituted hydroxypropyl cellulose, pectins, potassium methacrylate-divinylbenzene copolymer, poly(vinyl alcohol), thylamide, sodium bicarbonate, sodium carbonate, starch derivatives, dextrin, beta cyclodextrin, dextrin derivatives, magnesium oxide, clays, bentonite and mixtures thereof. 
     The active ingredient of the present invention may be mixed with excipients which are pharmaceutically acceptable and compatible with the active ingredient and in amounts suitable for use in the therapeutic methods described herein. Various excipients may be homogeneously mixed with the aminopyridines of the present invention as would be known to those skilled in the at. For example, aminopyridines may be mixed or combined with excipients such as but not limited to microcrystalline cellulose, colloidal silicon dioxide, lactose, starch, sorbitol, cyclodextrin and combinations of these. 
     Lubricants that am suitable for use in the pharmaceutical composition of the present invention include agents that act on the flowability of the powder to be compressed include but am not limited to silicon dioxide such as Aerosil 200, talc; stearic acid, magnesium stearate, calcium stearate, hydrogenated vegetable oils, sodium benzoate, sodium chloride, leucine carbowax, magnesium lauryl sulfate, and glyceryl monostearate. 
     To further improve the stability of the aminopyridine in the sustained release composition, an antioxidant compound can be included. Suitable antioxidants include, for example: sodium metabisulfite; tocopherols such as α, β, δ-tocopherol esters and α-tocopherol acetate; ascorbic acid or a pharmaceutically acceptable salt thereof; ascorbyl palmitate; alkyl gallates such as propyl gallate, Tenox PG, Tenox s-1; sulfites or a pharmaceutically acceptable salt thereof; BHA; BHT; and monothioglycerol. 
     In another embodiment, the pharmaceutical composition of the present invention comprises a rate-controlling polymeric matrix comprising of a hydrogel matrix. For instance, an aminopyridine may be compressed into a dosage formulation containing a rate-controlling polymer, such as HPMC, or mixture of polymers which, when wet, will swell to form a hydrogel. The rate of release of the aminopyridine from this dosage formulation is sustained both by diffusion from the swollen tablet mass and by erosion of the tablet surface over time. The rate of release of the aminopyridine may be sustained both by the amount of polymer per tablet and by the inherent viscosities of the polymers used. 
     According to another aspect of the invention, there is provided a stable, sustained-release oral dosage formulation which includes an effective amount a aminopyridine dispersed in a release matrix, and which, upon administration to a patient or as pan of a therapy regiment, provides a release profile (of therapeutically effective blood plasma level of the aminopyridine) extending for a period of at least 6 hours, preferably at least 12 hours, and more preferably at least 24 hours. In another embodiment, the stable, controlled-release oral dosage form provides, upon administration to a patient, a therapeutically effective blood plasma level of the aminopyridine for a period of at least 6 hours, preferably at least 12 hours, and mort preferably at least 24 hours. 
     The dosage formulation may assume any form capable of delivering orally to a patient a therapeutically effective amount of a aminopyridine dispersed in a rate-controlling polymer. Preferably, the dosage formulation comprises a monolithic tablet. 
     Tablet weight will also vary in accordance with, among other things, the aminopyridine dosage, the type and amount of rate-controlling polymer used, and the presence, types and amounts of additional materials. Assuming 4-aminopyridine dosages of from about 2 mg to about 120 mg; tablet weights can range from about 50 mg to about 1200 mg per tablet, and preferably from 250 to 500 mg, and more preferably about 400 mg. 
     The dosage formulation of the present invention may comprise also one or more pharmaceutically acceptable excipients as mentioned above. In preferred embodiments, the dosage formulation will comprise diluents and a lubricant in addition to the aminopyridine unit dose and the rate-controlling polymer. A particularly preferred diluents is microcrystalline cellulose sold under the name Avicel PH101, and a particularly preferred lubricant is magnesium stearate. When these materials are used, the magnesium stearate component preferably comprises from about 0.2 to about 0.75% w/w of the dosage formulation, and the microcrystalline cellulose along with the rate controlling polymer and aminopyridine comprises the balance of the formulation. For example, a tablet formulation including a aminopyridine x % w/w, a rate-controlling polymer y % w/w, and microcrystalline cellulose z %, the magnesium stearate amount would be (100−(x+y+z)) where 0.2%≤(100−(x+y+z))≤0.75% w/w. As would be known to those skilled in the art, the amount of an additives such as magnesium stearate may vary depending upon the shear rate used to perform the mixing and the amount of such an additive may be changed without limitation to obtain a satisfactory dissolution rate or plasma level of the aminopyridine. 
     As used herein, the term “sustained-release” includes the release of a aminopyridine from the dosage formulation at a sustained rate such that a therapeutically beneficial blood level below toxic levels of the aminopyridine is maintained over a period of at least about 12 hours, preferably about 24 hours or more. Preferably, the amount of the aminopyridine in the oral dosage formulations according to embodiments of the present invention establish a therapeutically useful plasma concentration through BID administration of the pharmaceutical composition. 
     If desired, the dosage formulations of this invention may be coated with a sustained-release polymer layer so as to provide additional sustained-release properties. Suitable polymers that can be used to form this sustained release layer include, for example, the release matrices listed above. As desired, the dosage formulation of the invention can be provided also with a light-protective and/or cosmetic film coating, for example, film-formers, pigments, anti-adhesive agents and politicizes. Such a film-former may consist of fast-dissolving constituents, such as low-viscosity hydroxypropylmethylcelluose, for example, Methocel ES or D14, or Pharmacoat 606 (Shin-Etsu). The film coating may also contain excipients or enteric coatings customary in film-coating procedures, such as, for example, light-protective pigments, for example, iron oxide, or titanium dioxide, anti-adhesive agents, for example, talc, and also suitable plasticizers such as, for example, PEG 400, PEG 6000, diethyl phthalate or triethyl citrate. 
     The compositions of the present invention may be used for the treatment of neurological diseases characterized by a degradation of nerve impulse transmission by administering to a patient the oral dosage formulation of the present invention. Preferably, the administration is twice daily dosage of a therapeutically effective amount of an aminopyridine, even more preferably, 4-AP dispersed in HPMC. The administration can also include scheduling administration of doses of the pharmaceutical so that the concentration of the aminopyridine in the patient is at about the minimum therapeutically effective level to ameliorate the neurological condition, yet relatively lower compared to the maximum concentration in order to enhance restful periods for the patient during the day. The compositions may be administered to a subject at a dose and for a period sufficient to allow said subject to tolerate said dose without showing any adverse effects and thereafter increasing the dose of said active agent in the tablets at selected intervals of time until a therapeutic dose is achieved in the subject. For example, at the commencement of treatment the active agent is preferably administered at a dose less than 15 mg/day until a tolerable state is reached. The dose administered may then be increased by amounts of at least 5-15 mg/day until a therapeutic dose is reached. For other diseases the amount of the aminopyridine required to reach a therapeutically effective amount for treatment is described in U.S. Pat. No. 5,952,357 the contents of which are incorporated herein by reference in their entirety. 
     Compositions of the present invention where the potassium channel blocker is a mono- or di-aminopyridine active agent are particularly suitable for use in the treatment of a neurological disease which is characterized by demyelination of the central nervous system, more especially multiple sclerosis. The mono- or di-aminopyridine active agent in accordance with the invention is also suitable for the treatment of Alzheimer&#39;s disease. Additional features and embodiments of the present invention are illustrated by the following non-limiting examples. 
     Example 1 
     This example illustrates preparation of compositions of the present invention and their release of an aminopyridine. Tablets in accordance with the present invention having dosages of 5 mg, 7.5 mg and 12.5 mg respectively were manufactured at 5 Kg scale. Materials were used in the amounts shown in Table 1. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                   
                 % w/w 
                 % w/w 
                 % w/w 
               
               
                   
               
               
                 Milled 4-AP (#50 mesh) 
                 1.25 
                 1.875 
                 3.125 
               
               
                 Methocel K100LV 
                 60 
                 60 
                 60 
               
               
                 Avicel PH101 
                 38.15 
                 37.525 
                 36.275 
               
               
                 Magnesium stearate 
                 0.2 
                 0.2 
                 0.2 
               
               
                 Aerosil 200 
                 0.4 
                 0.4 
                 0.4 
               
            
           
           
               
               
            
               
                 Equipment Tablet Press 
                 Horn Noak equipped with 13 × 8 mm oval tooling 
               
               
                   
                 press speed 42,000 tablets/hr 
               
            
           
           
               
               
               
               
            
               
                 Tablet Weight Range (mg) 
                 386-404 (96.5- 
                 388-410 (97.0- 
                 388-406 (97.0- 
               
               
                   
                 101.0%) 
                 102.5%) 
                 101.5%) 
               
               
                 Tablet Hardness Range (N) 
                 200-262 
                 179-292 
                 150-268 
               
               
                 Tablet Potency - mg/tab. (% LC) 
                 97.1 
                 99.1 
                 100.2 
               
               
                 Mean CU (mg/tab.)/% CV 
                 5.0 mg/1.0% 
                 7.4 mg/0.7% 
                 12.4 mg/1.1% 
               
               
                 CU Discrete Samples 
                 5.0 mg/1.2% 
                 7.5 mg/1.8% 
                   12.3/1.1% 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 (mg/tab.)/% CV 
                   
                   
                   
                   
                   
                   
               
               
                   
               
               
                 Dissolution (%/hr) 
                 Mean 
                 (SD) 
                 Mean 
                 (SD) 
                 Mean 
                 (SD) 
               
               
                   
               
               
                  1 
                 28.9 
                 1.1 
                 29.2 
                 1.8 
                 25.9 
                 1.1 
               
               
                  2 
                 42.7 
                 1.8 
                 42.1 
                 1.6 
                 40.2 
                 2.5 
               
               
                  3 
                 52.8 
                 1.4 
                 53.0 
                 1.0 
                 49.8 
                 2.1 
               
               
                  4 
                 61.4 
                 2.2 
                 61.8 
                 1.5 
                 60.1 
                 2.4 
               
               
                  6 
                 75.7 
                 3.1 
                 75.2 
                 1.6 
                 74.8 
                 2.7 
               
               
                 10 
                 95.5 
                 3.3 
                 98.7 
                 1.4 
                 93.2 
                 0.9 
               
               
                   
               
            
           
         
       
     
     Prior to blending, 4-AP was milled through #50 mesh screen using a Fitzmill® comminutor. The materials were added into a Gral 25 bowl in the following order: half Methocel K100LV, Avicel PH101, Aerosil 200, milled 4-AP and the remaining Methocel K100LV. The mix was blended for 15 minutes at 175 rpm, then the magnesium stearate was added and was further blended for 5 minutes at 100 rpm. Samples were taken from top and bottom positions for blend potency analysis. Weight and hardness checks were performed every 15 minutes by the check-master E3049. Discrete tablet samples were taken during the compression process to evaluate intra batch content uniformity. 
     Example 2 
     This example illustrates that the pharmacokinetic profile of fampridine in compositions of the present invention is altered by administration in a sustained release tablet matrix compared to immediate release and controlled release formulations. 
     There is a delay in absorption manifested by a lower peak concentration, without any effect on the extent of absorption. When given as a single 12.5 mg dose, the peak concentration is approximately two-thirds lower as compared to peak values following administration of the IR formulation; the time to reach peak plasma levels was delayed by about 2 hours.  FIG.  1    is a graph of mean plasma profiles associated with the administration to a patient in both fasted and fed states of a tablet form of 4-AP (fampridine) in accordance with the present invention compared with the mean plasma profile associated with the administration of an immediate release (IR) formulation. As with the IR formulation, food delayed the absorption of Fampridine-SR. The absorption of fampridine was approximately 50% slower following ingestion of a fatty meal, although due to the flatness of the absorption curve, this may be exaggerated value. Extent of absorption did not differ, as values for Cmax and AUC were comparable as summarized in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Pharmacokinetic Parameter Values (Mean ± SD) in Studies Using Fampridine 
               
               
                 SR, CR, and IR Formulations: Single Dose Studies in Healthy Adult Male Volunteers 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                 C MAX   
                 t MAX   
                 AUC (0-∞) 
               
               
                 Study Number 
                 Dose (mg) 
                 Fed/Fasted 
                 (ng/mL) 
                 (hours) 
                 (ng hr/mL) 
               
               
                   
               
               
                 0494006 
                 12.5 SR 
                 Fed 
                 28.7 ± 4.3 
                 5.3 ± 0.8 
                 257.0 ± 62.7 
               
               
                 N = 12 
                 (PD12265) 
                 Fasted 
                 25.6 ± 3.8 
                 2.8 ± 1.3 
                 269.9 ± 44.4 
               
               
                   
                 12.5 IR 
                 Fasted 
                  79.3 ± 16.3 
                 0.9 ± 0.4 
                 294.2 ± 55.6 
               
               
                   
                 (PD12266) 
               
               
                 1194002 
                 12.5 SR 
                 Fasted 
                 28.5 ± 4.3 
                 2.9 ± 2.4 
                 285.9 ± 37.8 
               
               
                 N = 12 
                 (PD12907) 
               
               
                   
                 12.5 CR 
                 Fasted 
                 37.7 ± 9.9 
                 3.6 ± 0.9 
                 300.0 ± 53.6 
               
               
                   
                 (4n806) 
               
               
                   
                 12.5 IR 
                 Fasted 
                  83.5 ± 23.5 
                 0.79 ± 0.3  
                 274.0 ± 59.2 
               
               
                   
                 (PS644) 
               
               
                   
               
            
           
         
       
     
       FIG.  2    is a graph of mean plasma profiles associated with the administration of a tablet form of 4-AP (fampridine) in accordance with the present invention compared with the mean plasma profile associated with the administration of a sustained-release capsule of the present invention and an immediate release capsule. 
     Example 3 
     This example details the plasma concentration of different dosage tablets of a aminopyridine in compositions of the present invention administered to patients with spinal cord injury. Pharmacokinetic results are presented for the subset of 11 patients who completed all dose levels. Maximal plasma concentrations and AUC values increased with increasing dose, with a mean C max  of 152.0 ng/mL at the highest dose of 120 mg/day. The time of the peak and the plasma elimination half-lives were independent of dose. Mean T max  ranged from 2.2 hours to 3.0 hours. The T 1/2  of fampridine ranged from 5.7 to 6.9 hours. There were no apparent differences between males and females. Data from this study are summarized in Table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Pharmacokinetic Parameter Values (Mean ± SD) Following 
               
               
                 Multiple Oral Doses of Fampridine-SR to 11 Patients with SCI. 
               
            
           
           
               
               
               
               
               
            
               
                 Fampridine -SR 
                   
                   
                   
                   
               
               
                 Dosage 
                 C MAX   
                 T MAX   
                 AUC (0-12)   
                 T 1/2   
               
               
                 (mg b.i.d.) 
                 (ng/mL) 
                 (hours) 
                 (ng hr/mL) 
                 (hours) 
               
               
                   
               
               
                 25 
                  63.4 ± 11.9 
                 2.2 ± 0.9 
                 475.8 ± 65.5 
                 6.4 ± 1.4 
               
               
                 30 
                  83.2 ± 20.5 
                 2.4 ± 1.4 
                  600.0 ± 128.0 
                 6.7 ± 3.8 
               
               
                 35 
                  90.2 ± 14.4 
                 2.4 ± 1.2 
                  660.3 ± 137.7 
                 6.9 ± 3.4 
               
               
                 40 
                 103.2 ± 19.4 
                 2.6 ± 1.3 
                  771.5 ± 135.3 
                 6.6 ± 2.1 
               
               
                 50 
                 145.7 ± 27.9 
                 3.0 ± 1.9 
                 1047.6 ± 258.8 
                 5.8 ± 1.9 
               
               
                 60 
                 152.0 ± 25.2 
                 3.0 ± 2.0 
                 1075.0 ± 163.0 
                 5.7 ± 2.3 
               
               
                   
               
            
           
         
       
     
     Example 4 
     This example details the pharmacokinetic properties of Fampridine-SR in tablets of the present invention administered to patients with multiple sclerosis. Plasma samples were analyzed for fampridine using a validated LC/MS/MS assay with a sensitivity of 2 ng/mL. Noncompartmental pharmacokinetic parameter values were calculated using standard methodology. 
     This was an open-label, multi-center, dose proportionality study of orally administered fampridine in patients with multiple sclerosis. Single doses of fampridine were to be given in escalating doses (5 mg, 10 mg, 15 mg, and 20 mg) with at least a four-day interval between administration of each dose of drug. Safety evaluations were to be performed during the 24 hour period following administration of fampridine and blood samples were to be taken at the following times to determine pharmacokinetic parameters: hour 0 (pre-dose), hours 1-8, and hours 10, 12, 14, 18, and 24. 
     Twenty-three subjects received all 4 treatments, and one subject received only 3 treatments; data from all treatments were analyzed. Dose-dependent parameters (e.g., peak plasma concentration and areas-under-the curve) were normalized to a 10 mg dose for among-dose comparisons. Overall observed tire of the peak plasma concentration (mean and its 95% confidence interval) was 3.75 (3.52, 3.98) h, observed peak plasma fampridine concentration (normalized to a 10 mg dose) was 24.12 (23.8, 26.6) ng/ml, area-under-the-concentration-time curve (normalized to a 10 mg dose) was estimated to be 254 (238, 270)ng-h/ml, extrapolated area-under-the-concentration-time curve (normalized to a 10 mg dose) was 284 (266, 302) ng-h/ml, terminal rate constant equaled 0.14 (0.13, 0.15) h −1 , terminal half-life was 5.47 (5.05, 5.89) h and clearance divided by bioavailability (CL/F) was equal to 637 (600, 674) ml/min. 
     Dizziness was the most common treatment-related adverse event. Other treatment related adverse events included amblyopia, asthenia, headache, and ataxia. There were clinically significant changes in clinical laboratory values, ECG parameters, vital signs, physical examination findings, or neurological examination findings noted over the course of this study. 
     When the plasma concentrations of fampridine were normalized to the 10.0 mg dose levels, there were no significant differences between any pharmacokinetic parameter (AUC, C max , t 1/2 ) in the 5-20 mg dose range. Fampridine was well tolerated at the doses used in this study. Dose-normalized (to a 10 mg dose) pharmacokinetic parameter values are summarized in Table 4. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Dose-Normalized (at 10 mg) Pharmacokinetic Parameter 
               
               
                 Values (Mean ± SEM) Following Single Oral Administration 
               
               
                 of Fampridine-SR to Patients with MS. 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 C MAX - 
                   
                 AUC- 
                   
                   
               
               
                 Dose 
                 norm 
                 t MAX   
                 norm 
                 t 1/2   
                 Cl/F 
               
               
                 (mg) 
                 (ng/mL) 
                 (hours) 
                 (ng hr/mL) 
                 (hours) 
                 (mL/min) 
               
               
                   
               
               
                  5 
                 26.2 ± 0.6 
                 3.9 ± 0.2 
                 244.2 ± 9.4 
                 5.8 ± 0.5 
                 619.8 ± 36.2 
               
               
                 (n = 24) 
               
               
                 10 
                 25.2 ± 0.7 
                 3.9 ± 0.3 
                 252.2 ± 7.8 
                 5.6 ± 0.4 
                 641.4 ± 39.1 
               
               
                 (n = 24) 
               
               
                 15 
                 24.6 ± 0.7 
                 3.6 ± 0.3 
                 263.0 ± 7.4 
                 5.5 ± 0.4 
                 632.4 ± 39.0 
               
               
                 (n = 24) 
               
               
                 20 
                 24.6 ± 0.8 
                 3.6 ± 0.3 
                 255.6 ± 6.9 
                 5.1 ± 0.3 
                 653.9 ± 37.1 
               
               
                 (n = 23) 
               
               
                   
               
            
           
         
       
     
     Example 5 
     This example describes the results of an open-label study to assess the steady state pharmacokinetics of orally administered fampridine (4-aminopyridine) compositions of the present invention in subjects with Multiple Sclerosis. This study was an open-label multiple dose study of Fampridine-SR intended to assess steady state pharmacokinetics in 20 patients with MS who previously completed the study summarized in Table 4. Fampridine-SR (40 mg/day) was administered as two 20 mg doses, given as one morning and one evening dose for 13 consecutive days, with a single administration of 20 mg on Day 14. Blood samples for pharmacokinetic analysis were collected on Days 1, 7/8, and 14/15 at the following intervals: immediately prior to drug administration (baseline), hourly for the first 8 hours, and 10, 12, and 24 hours post-dose. Additional blood samples were collected 14, 18, and 20 hours post-dose on Day 14, and 30 and 36 hours post-dose on Day 15. 
     Pharmacokinetic parameter estimates following the first dose in these patients in this study on Day 1 were comparable to those determined when they participated in the study summarized in Table 4. No significant difference in T max  was detected among the four means (Single dose=3.76 h; Day 1=3.78 h; Day 8=3.33 h; Day 15=3.25 h). C max  and C max /C τ  on Days 8 (C max =66.7 ng/ml) and 15 (C max =62.6 ng/ml) were significantly greater than those of the single dose treatment and of Day 1(C max =48.6 ng/ml), reflecting accumulation of the dag with multiple dosing. 
     There was no significant difference among the four occasions with regard to either T or C and no difference in C max ; C max /C τ , CLP or AUC 0-τ  between Days 8 and 15. Further AUC on Days 8 and 15 did not differ significantly from total AUC with single dose treatment. Likewise, the estimates of CUP on Days 8 and 15 and of λ and T 1/2  on Day 15 did not differ significantly from those with single dose. 
     Steady-state was attained by Day 7/8 as evidence by the lack of differences in C max  or AUC between Days 7/8 and 14/15; there was no apparent unexpected accumulation. Likewise, the estimates of Cl/F on Days 7/8 and 14/15 of and of T 1/2  on Day 14/15 did not differ significantly from those given a single dose. On the final day of dosing, mean C max  was 62.6 ng/mL, occurring 3.3 hours post-dose. The T 1/2  was 5.8 hours. These values are similar to those observed in patients with chronic SCI receiving similar doses of this formulation. These results are summarized in Table 5. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Pharmacokinetic Parameter Values (Mean and 95% 
               
               
                 CI) Following Multiple Oral Doses of Fampridine-SR 
               
               
                 (40 mg/day) to 20 Patients with MS. 
               
            
           
           
               
               
            
               
                   
                 Parameter 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 C MAX   
                 t MAX   
                 AUC (0-12)   
                 t 1/2   
                 Cl/F 
               
               
                 Day 
                 (ng/mL) 
                 (hours) 
                 (ng hr/mL) 
                 (hours) 
                 (mL/min) 
               
               
                   
               
               
                 Day 1 
                 48.6 
                 3.8 
                 NE 
                 NE 
                 NE 
               
               
                   
                 (42.0, 55.3) 
                 (3.2, 4.3) 
               
               
                 Day 7/8 
                 66.7 
                 3.3 
                 531 
                 NE 
                 700 
               
               
                   
                 (57.5, 76.0) 
                 (2.8, 3.9) 
                 (452, 610) 
                   
                 (557, 884) 
               
               
                 Day 
                 62.6 
                 3.3 
                 499 
                 5.8 
                 703 
               
               
                 14/15 
                 (55.7, 69.4) 
                 (2.6, 3.9) 
                 (446, 552) 
                 (5.0, 6.6) 
                 (621, 786) 
               
               
                   
               
            
           
         
       
     
     Dizziness was the most common treatment-related adverse event. Other treatment-related adverse events that occurred included nausea, ataxia, insomnia, and tremor. There were no clinically significant changes in mean clinical laboratory values, vital sips, or physical examination findings from baseline to last visit. There were no apparent clinically significant changes in corrected QT intervals or QRS amplitudes after administration of fampridine. 
     Fampridine was well tolerated in subjects with multiple sclerosis who receive twice daily doses (20 mg/dose) of fampridine for two weeks. A significant increase was observed in C max , and C max /C τ  on Days 8 and 15 relative to those on Day 1 and with single dose treatment, reflecting accumulation of fampridine with multiple dosing. A lack of significant differences in C max , C max /C τ , CL/F or AUC 0-τ  between Days 8 and 15 suggest that near steady-state is reached by Day 8. There was no evidence of significant pharmacokinetics during a two-week period of multiple dosing with fampridine. 
     Example 6 
     This was an open-label, single dose, single-center study of the pharmacokinetics and tolerability of escalating doses of orally administered Fampridine-SR in fourteen (14) patients with chronic incomplete SCI. 
     After fasting overnight, a single oral dose of Fampridine-SR (10, 15, 20, or 25 mg) was to be administered. Each patient was to receive each dose in an ascending fashion. Each dose was to be followed by a 7-day washout period. A single dose of Fampridine-SR was to be administered orally on Day 1-10 mg, Day 8-15 mg, Day 15-20 mg and Day 22-25 mg with 240 mL of tepid water at approximately the same time on each treatment day. Patients were to continue their fast for 4 hours after dosing and then a standard meal was to be served. Blood samples for pharmacokinetic analysis were to be obtained at Hour 0 (immediately preceding study drug administration) and 1, 2, 3, 4, 5, 6, 8, 10, 12, 16, 20, and 24 hours after each dose. A baseline urine sample was to be collected prior to dosing and urine was to be collected for 24 hours after administration of the study drug at the following intervals: 0.1 to 4 hours; 4.1 to 8 hours; 8.1 to 12 hours; and 12.1 to 24 hours. 
     There was no detectable fampridine in any of the pre-dose plasma samples. By visual inspection of plasma concentration-time curves, concentrations were seen to rise for up to the first 4 hours post-dose and then to decline in a monophasic fashion. In some patients, there was evidence of a second peak. Peak concentrations increased proportionally with dose, with mean C MAX  of 27.7 ng/mL following a single dose of 10 mg and mean C MAX  of 67.4 ng/mL following a single dose of 25 mg. Peak concentrations occurred 3 to 4 hours post-dose, regardless of dose level. AUC also increased proportionally with increasing dose. The length of sampling was adequate since AUC 0-24  is at least 92% of AUC 0-8 . The mean T 1/2  was independent of dose, approximately 6 hours. Pharmacokinetic parameter values by dose are summarized in the Table 6 below. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Mean (±SD) pharmacokinetic parameters of fampridine-SR 
               
               
                 following single dose administration 
               
            
           
           
               
               
            
               
                   
                 Fampridine-SR dose 
               
            
           
           
               
               
               
               
               
            
               
                   
                 10 mg 
                 15 mg 
                 20 mg 
                 25 mg 
               
               
                 Parameter 
                 n = 14 
                 n = 14 
                 n = 14 
                 n = 13* 
               
               
                   
               
               
                 C max  (ng/mL) 
                 27.7 ± 9.1  
                 43.5 ± 11.2 
                 54.9 ± 11.0 
                 67.4 ± 13.3 
               
               
                 t max  (h) 
                 3.2 ± 1.0 
                 3.5 ± 1.2 
                 3.5 ± 1.0 
                 3.7 ± 1.2 
               
               
                 AUC 0-24 h  (ng · h/mL) 
                 285.4 ± 96.8  
                 423.0 ± 98.6  
                 561.1 ± 117.6 
                 715.6 ± 150.0 
               
               
                 AUC 0-∞  (ng · h/mL) 
                 311.8 ± 93.2  
                 460.2 ± 100.2 
                 604.3 ± 124.6 
                 769.2 ± 154.4 
               
               
                 K el  (h −1 ) 
                 0.13 ± 0.03 
                 0.12 ± 0.03 
                 0.12 ± 0.02 
                 0.13 ± 0.03 
               
               
                 t 1/2  (h) 
                 5.9 ± 1.5 
                 5.9 ± 1.5 
                 5.9 ± 1.4 
                 5.8 ± 1.6 
               
               
                 Cl/F (L/h) 
                 34.8 ± 10.2 
                 34.3 ± 8.9  
                 34.7 ± 8.5  
                 34.0 ± 8.3  
               
               
                 V d /F (L) 
                 299.8 ± 127.4 
                 289.0 ± 93.7  
                 289.9 ± 84.1  
                 286.2 ± 123.2 
               
               
                   
               
               
                 *One patient was excluded from analysis, as not all blood samples were collected. 
               
               
                 C max , maximum observed plasma concentration; t max , time to reach C max ; AUC, area under the plasma concentration-time curve; K el , elimination rate constant; t 1/2 , plasma half-life; Cl/F, apparent total clearance; V d /F, apparent volume of distribution. 
               
            
           
         
       
     
     Fampridine pharmacokinetic parameters following the oral administration of single doses of fampridine-SR (10-25 mg) are summarized in Table 6. Fampridine-SR was slowly absorbed (mean t max  occurring 3.2 to 3.7 hours postdose) and slowly eliminated in a monophasic manner (mean t 1/2 ˜5.9 hours). Mean t 1/2 , k el , V d /F, and Cl/F were independent of dose over the dose range (10-25 mg), while mean C max , AUC 0-24h , and AUC 0-∞  were linearly related to dose. AUC 0-24h  was at least 92% of AUC 0-∞  Mean C max  for the lowest fampridine-SR dose (10 mg) was 27.7 ng/mL, while mean C max  for the highest dose (25 mg) was 67.4 ng/ML. 
     The plasma concentration profile following administration of Fampridine-SR was consistent with a sustained release of drug. Peak concentrations of fampridine occurred on average 3 to 4 hours post-dose, and concentrations declined with a plasma half-life of approximately 6 hours. The results of this study indicate that Fampridine-SR pharmacokinetics are linear over the single dose range studied, 10 to 25 mg. Area under the curve (AUC) and peak plasma concentration (C max ) increased proportionally with dose. 
     Fampridine-SR was well-tolerated over the range of single oral doses administered in this study. Dizziness was the most frequently reported adverse event. The next most common events were hypotension, nausea, and paresthesia. There was no clear relationship between dose level and frequency of adverse events, except with the possibility of nausea, which only occurred at the 25 mg dose. There were no clinically significant changes in vital signs during treatment. 
     The pharmacokinetic analysis of Fampridine-SR administered once weekly showed dose proportionality across single oral doses of 10, 15, 20, and 25 mg. Mean peak fampridine concentration increased linearly with dose from 27.7 ng/mL following a dose of 10 mg to 69.9 ng/mL following a dose of 25 mg. Absorption was prolonged with peak concentrations occurring on average 3 to 4 hours postdose; this was independent of dose. The mean T % appeared independent of dose, approximately 6 hours. Single oral doses of 10, 15, 20, and 25 mg of Fampridine-SR were well-tolerated, as assessed by adverse event reporting, clinical laboratories, vital sign measurements, physical examinations, and ECO interpretation. 
     Example 7 
     This example describes the results of an open-label, multiple dose, single center study to assess the effects of escalating doses of orally administered sustained release fampridine (4-aminopyridine) in sixteen (16) patients with chronic incomplete spinal cord injury (SCI). Sustained release tablets of fampridine were administered 10 mg twice daily for 1 week, 15 mg twice daily for 1 week, 20 mg twice daily for 1 week and 25 mg twice daily for 1 week in sixteen patients with SCI. 
     Following administration of Fampridine-SR, fampridine was slowly adsorbed, with peak concentration observed approximately three hours post-dose, regardless of dose (p=0.227). Plasma levels declined gradually with a half life of 6 to 7 hours, independent of dose. Based on the mean trough concentrations, steady state was achieved by Day 5. Steady state maximal, minimal, and average plasma concentrations and AUC increased with increasing dose. Total clearance ranged between 9 and 10 mL/min/kg across dose groups. Volume of distribution at steady state ranged from 2.01 L/kg in the 15 mg BID dose group to 2.11 L/kg in the 20 mg BID dose group. A summary of the mean pharmacokinetic results is provided in Table 7. 
     Fampridine pharmacokinetic parameters following the oral administration of multiple doses of fampridine-SR (10-25 mg BID) are summarized in Table 7. Mean t max  and t 1/2  were similar to values found in the single-dose study (compare to Table 6). Steady state was achieved by Day 5 (4 days of fampridine-SR dosing) following twice-daily administration of fampridine-SR. Mean t max , t 1/2 , K el , V ss /F, Cl/F, and mean residence time at steady state (MRT ss ) were independent of dosage following the administration of fampridine-SR (10-25 mg BID). Mean plasma concentrations (C maxss , C avss , and C minss ) and AUC 0-12h  at steady state were linearly related to dose over the dosage range (fampridine-SR 10-25 mg BID). Mean C maxss  at steady state for the lowest fampridine-SR dosage (10 mg BID) was 32.2 ng/mL and was 87.2 ng/mL for the highest fampridine-SR dosage (25 mg BID). Corresponding C minss  values for the lowest and highest dosages were 14.0 and 41.3 ng/mL. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Mean (±SD) pharmacokinetic parameters of fampridine-SR 
               
               
                 following multiple dose administration 
               
            
           
           
               
               
            
               
                   
                 Fampridine-SR dose 
               
            
           
           
               
               
               
               
               
            
               
                   
                 10 mg BID 
                 15 mg BID 
                 20 mg BID 
                 25 mg BID 
               
               
                 Parameter 
                 n = 15 
                 n = 15 
                 n = 14 
                 n = 14 
               
               
                   
               
               
                 C maxss  (ng/mL) 
                 32.2 ± 8.9  
                 46.7 ± 10.5 
                 60.1 ± 15.0 
                 87.2 ± 29.0 
               
               
                 C minss  (ng/mL) 
                 14.0 ± 4.4  
                 23.5 ± 9.1  
                 27.3 ± 10.0 
                 41.3 ± 15.2 
               
               
                 C avss  (ng/mL) 
                 20.8 ± 5.7  
                 31.0 ± 7.2  
                 39.4 ± 9.3  
                 53.3 ± 14.5 
               
               
                 t max  (h) 
                 2.7 ± 1.0 
                 3.2 ± 0.9 
                 3.1 ± 1.2 
                 2.6 ± 0.9 
               
               
                 AUC 0-12 h  (ng · h/mL) 
                 249.3 ± 68.3  
                 371.8 ± 86.8  
                 472.3 ± 111.8 
                 639.4 ± 173.9 
               
               
                 K el  (h −1 ) 
                 0.14 ± 0.05 
                 0.12 ± 0.03 
                 0.13 ± 0.04 
                 0.12 ± 0.05 
               
               
                 t 1/2  (h) 
                 5.6 ± 1.8 
                 6.0 ± 1.5 
                 5.8 ± 2.1 
                 7.6 ± 5.5 
               
               
                 Cl/F (L/h/kg) 
                 9.52 ± 2.85 
                 9.35 ± 2.44 
                 9.79 ± 2.03 
                 9.15 ± 2.35 
               
               
                 V ss /F (L/kg) 
                 2.22 ± 0.79 
                 2.01 ± 0.59 
                 2.11 ± 0.51 
                 2.09 ± 0.65 
               
               
                 MRT ss  (h) 
                 5.18 ± 0.21 
                 5.18 ± 0.30 
                 5.15 ± 0.35 
                 5.08 ± 0.31 
               
               
                 Accumulation factor 
                 1.30 ± 0.18 
                 1.34 ± 0.16 
                 1.32 ± 0.22 
                 1.53 ± 0.62 
               
               
                   
               
               
                 C maxss , maximum observed plasma concentration at steady state; C minss , minimum observed plasma concentration at steady state; C avss , average plasma concentration at steady state; t max , time to reach C max ; AUC, area under the plasma concentration-time curve; K el , elimination rate constant; t 1/2 , plasma half-life; Cl/F, apparent total clearance; V ss /F, apparent volume of distribution at steady state; MRT ss , mean residence time at steady state; BID, twice daily. 
               
            
           
         
       
     
     Adverse events included pain, hypertonia, dizziness, accidental injury, dyspepsia, asthenia, urinary tract infection and euphoria. There was no clear relationship between frequency of adverse events and dose level, however euphoria and dizziness were observed more frequently in the 25 mg BID dose level. 
     Multiple oral doses of 10, 15, 20 and 25 mg BID of Fampridine-SR were generally well-tolerated, as assessed by adverse event reporting, clinical laboratories, vital signs, and physical examinations. The pharmacokinetic analysis of Fampridine-SR showed dose proportionality across multiple oral doses of 10, 15, 20, 25 mg BID each administered for 1 week. The results demonstrate that fampridine pharmacokinetics are linear over the dose range studied. Trough values indicated that steady state had been achieved by Day 5. Fampridine pharmacokinetics are dose-proportional: both AUC and C max  at doses of 10, 15, 20, and 25 mg BID, each administered over the course of one week, were dose-proportional under both and ANOVA model and a regression power model. Neither rate of absorption (as reflected by the time of the peak concentration) nor the rate of elimination (K) were dependent on dose. 
     Example 8 
     This was a double-blind, placebo-controlled, 20 week, parallel-group study to evaluate safety, tolerability and activity of oral fampridine-SR in subjects with Multiple Sclerosis. The study was designed as follows: a two-week placebo run-in (single blind); a two-week upward titration (10 mg bid, 15 mg bid or placebo); a twelve-week stable treatment period (placebo, 10 mg bid, 15 mg bid or 20 mg bid); a one-week downward titration (10 mg bid, 15 mg bid or placebo) and a two-week post treatment follow-up. A total of 206 patients were enrolled in the study. 
     The mean change in walking speed, the walking speed measured per visit, the mean change in LEMMT, the LEMMT per visit, the adverse events and serious adverse events associated with the study were documented. 
     Results. The trial showed a strong positive trend across all three dose groups compared to placebo in its primary endpoint, improvement in walking speed, as measured by a timed 25-foot walk as shown in  FIG.  3   . The trial also showed a statistically significant improvement across dose groups in its secondary endpoint, the Lower Extremity Manual Muscle Test (LEMMT), as shown in  FIG.  4   . These results confirmed observations in earlier double-blind trials that involved fewer subjects and shorter treatment periods. Because most people with MS experience both impairment in walking ability and weakened muscles, the Timed 25 Foot Walk is widely-used to assess MS patients&#39; functional status. The LEMMT is a standardized, 5-point manual assessment of strength, applied to leg muscle groups. The study showed a statistically significant difference across all doses at up-titration and follow-up for the 25 foot walk. The study also showed a statistically significant improvement in LEMMT across all doses during stable treatment. The study confirms the safety profile of 4-aminopyridine and preferable dosing of 10 to 15 milligrams twice daily. 
     Fampridine-SR showed a strong positive trend in the improvement of walking speed and significantly improved leg muscle strength in people with multiple sclerosis (MS). The drug also showed a reduction of muscle spasticity in people with chronic spinal cord injury (SCI). 
     Example 9 
     This was a group study to evaluate safety, tolerability and activity of oral fampridine-SR in subjects with spinal cord injury (SCI). The study was designed as follows: a two-week placebo run-in (single blind); a two-week upward titration (10 mg bid, 15 mg bid or placebo); a twelve-week stable treatment period (placebo, or 25 mg bid); a two-week downward titration (10 mg bid, 15 mg bid) and a two-week post treatment follow-up. A total of 204 patients were enrolled in the study, of which 166 completed. 
     The mean change in Ashworth score, the Ashworth score measured per visit, the mean change in LEMMT, the LEMMT per visit, the adverse events and serious adverse events associated with each study were documented. The Ashworth is a validated, 5-point clinician assessment of an individual&#39;s spasticity (the involuntary tension, stiffness or contraction of muscles.) 
     Results. The study showed a statistically significant improvement of Ashworth score using FDA-preferred analysis, as shown in  FIG.  5   . The study also confirmed the safety profile of 4-aminopyridine. 
     Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other versions are possible. Therefore the spirit and scope of the appended claims should not be limited to the description and the preferred versions contain within this specification.