SUSTAINED-RELEASE PHARMACEUTICAL COMPOSITIONS

Abstract: The present invention pertains to biodegradable sustained release pharmaceutical compositions. The compositions can be formed into implant devices which may be used to treat a wide variety of diseases and conditions. The implants are especially useful in treating diseases such such periodontal disease which require prolonged drug release.

Description: FIELD OF THE INVENTION : The present invention pertains to sustained-release pharmaceutical compositions, and more specifically to a biodegradable film which may be employed in the treatment of periodontal and other disease. BACKGROUND OF THE INVENTION A. Periodontal Disease The two major diseases of the oral cavity are dental caries, a disease process by which cavities are produced in the tooth surface, and periodontal disease, a process in which the bone and soft tissues supporting the tooth are destroyed. Periodontal diseases are a very common occurrence affecting, at a conservative estimate, between 70-90% of the world population and is the major cause of tooth loss in people over 35 years of age. Periodontal disease is an all-inclusive term for a variety of clinical conditions that are forms of either gingivitis or periodontis. Gingivitis is an inflammation of the gingiva (or gums) that can be associated with poor oral hygiene and/or the hormonal state of the patient. It is believed that gingivitis, if untreated, will develop into periodontis. Periodontis is a bacterial disease in which the infection has progressed to involve the oral tissues which retain the teeth in the jawbone. Periodontis, if untreated, will eventually result in the loss of the affected tooth. Although dental caries may be effectively treated with a combination of proper hygiene and fluoride, periodontal disease is often more refractile to treatment. This difference in amenability to treatment reflects the markedly different environments of the oral and periodontal cavities. The oral cavity is essentially an aerobic environment, which is constantly perfused by saliva. In contrast, the periodontal microenvironment is more anaerobic and is perfused by a plasma filtrate, known as the "gingival crevice fluid." The growth of microorganisms within this microenvironment has been shown to be the cause of periodontal disease (Loe, et al ., J. Periodontol . 36 :177 (1965); Slots, Scand. J. Dent. Res. , 85 :247 (1977); Socransky, S.S., J. Periodontol. 48 :497-504 (1977); Axelsson, P., et al ., J. Clin. Periodon. 5 :133-151 (1978)). Hence, the treatment of the disease is directed toward controlling this growth. As the periodontal disease becomes more established, the periodontal microenvironment becomes more anaerobic and the flow of gingival crevice fluid increases. An excellent review of periodontal disease, and the methods for its treatment, is provided by Goodson, J.M. ( In : Medical Applications of Controlled Release , Vol. II, Applications and Evaluation (Langer, R.S., et al ., Eds.), CRC Press, Inc., Boca Raton, FL (1984), pp. 115-138), which reference is incorporated by reference herein. Efforts to treat periodontal disease have been impeded by several factors. Because the site of the bacterial infection is largely inaccessible to agents present in the oral cavity, antimicrobial agents provided to the oral cavity are generally ineffective. The increased flow of gingival crevice fluid, which accompanies periodontal disease, has the effect of diluting and removing therapeutic agents placed within the periodontal crevice. Systemic administration of antibiotics has been shown to be a useful method of controlling the subgingival flora (Listgarten et al. , J. Clin. Periodont. 5 :246 (1978)), however discontinuation of therapy is often associated with the return of the potential pathogens to the pockets. Systemic administration, therefore, has had only variable success in treating periodontal disease (Genco, R.J., J. Periodontol . 52 :545 (1981)). Long-term antibacterial therapy has been used, but the potential dangers associated with this form of treatment, which include the development of resistant strains and super-imposed infections, do not warrant its serious consideration. Antibacterial agents such as chlorhexidine and quaternary ammonium salts in the form of mouth rinses have proved to be successful in preventing periodontal disease (Loe et al ., J. Periodont. Res. 5 :78 (1970)). These agents, however, are unable to affect the subgingival flora when administered in this form as they do not penetrate into the pockets which are the result of the disease. Hence, they cannot be used in mouth rinses to treat an established periodontal disease. Patient acceptance has significantly limited the utility of non-pharmacological treatments of periodontal disease. The most widely used non-pharmacological approach to date has been mechanical cleaning methods combined with surgery. Although this method has proved to be fairly successful in treating individuals, there is still a high recurrence rate. There is also the problem of motivating people to good oral hygiene habits that they will maintain throughout their lives. B. Use of Sustained Release Pharmaceutical Compositions in the Treatment of Periodontal and Other Diseases In response to the importance of treating periodontal disease, and the failure of conventional control therapies, researchers have developed control-release pharmaceutical compositions which are capable of being inserted into the periodontal cavity and of slowly releasing an antimicrobial agent. Goodson et al . ( J. Clin. Periodont. 6 :83 (1979); J. Periodont. Supp. - Special Issue 81-87 (1985)) proposed the use of a device that could be placed within the pockets and that would provide a sustained release of antibacterial agents to control the pocket flora. The system they described released the drug for up to 10 days. It appeared to cause marked changes in the pocket flora. The most investigated systems for controlled release comprise incorporating such a drug into a polymeric matrix, which is then shaped into a convenient form and implanted into the periodontal cavity. Ethyl cellulose has been successfully employed as a polymeric matrix of a periodontal implant (Friedman, M., et al ., J. Periodon. Res. 17 :323-328 (1982); Soskolne, A., et al ., J. Periodon. Res. 18 :330-336 (1983); Stabholz, A., et al ., J. Clin. Periodon. 13 :783-788 (1986)). Various antibacterial agents, such as chlorhexidine, metronidazole, iodine, cetyl puridinium chloride, have been incorporated into such ethyl cellulose films. Loesche, W.J. (U.S. Patent No. 4,568,535) discloses the use of periodontal implants composed of ethyl cellulose which contain metronidazole in the treatment of periodontal disease. Although such films were found to be effective in treating periodontal disease, their non-biodegradable nature required their removal after the conclusion of therapy. The usefulness of silicon rubbers as an implant material is well established (Folkman, J., et al ., Ann. N. Y. Acad. Sci. 111 :857 (1964)). However, even though such polymers are well tolerated by the tissue and are useful for a variety of drugs, their suitability as implants is seriously limited because the device must be surgically removed after use. Hence, a major therapeutic goal is the development of a biodegradable implant which would not need to be removed from the patient. Degradable polymers and copolymers which have been substantially investigated as potential implant compositions include poly(lactic acid) (Kulkarni et al ., Arch. Surg. 93 :839 (1966)), poly(glycolic acid) (Higgins, U.S. Patent 2,676,945 (1954)), and poly(lactic acid)-poly(glycolic acid) copolymer (Schmitt et al ., U.S. Patent 32,397,033 (1967)). The properties and uses of such polyamides and of copolymers of polyamides and polyesters have been extensively disclosed (Kurtz, French Patent No. 2,059,690 (1971); Kurtz, French Patent No. 2,059,691 (1971); Mori et al ., Japanese patent No. 72-43,220 (1972); Kurtz, U.S. Patent No. 3,642,003 (1970)). The biodegradation of poly(lactic acid) and poly(glycolic acid) can require three to five months (Schneider, French Patent No. 1,478,694 (1967); Darkik, Am. J. Surg. 121 :656 (1971)). Thus, it would not be preferable to employ implants composed of such polymers in situations where more rapid biodegradation is desired. Absorbable periodontal implants have been described by Noguchi, et al . ( Bull. Tokyo , Med. Dent. Univ. 31 :145 (1984)), which used a hydroxypropylcellulose polymer. Suzuki, Y., et al . (U.S. Patent No. 4,569,837) discloses the use of water-soluble polymeric substances (such as methyl cellulose, gelatin, etc.) as a polymeric matrix for a periodontal implant. Pharmaceutical compositions containing gelatin have been described by Lieb, H., et al . (U.S. Patent No. 2,961,374) and by Easton, I.A. (U.S. Patent No. 4,344,967). Despite the existence of the above-described sustained drug release compositions, a need still exists for a biodegradable sustained-release composition which is capable of delivering a pharmacological composition for a period of time sufficient to treat a periodontal infection. DE-A-2319852 relates to the preparation of absorbent collagen fibre substances for the uptake of drugs. Insoluble collagen is used together with a hardening agent (formaldehyde) and a softener (glycerin or propylene glycol). Incorporation of the drug is by using an aqueous solvent (such as alcohol) which dissolves the drug but not the collagen. FR-A-2342741 relates to injectable vaccine compositions having a solid biodegradable matrix, such as gelatin cross-linked with glutaraldehyde, containing an antigen material. A gelatin and antigen concentrate is dropped into paraffin oil to form spheres, which are then recovered from the paraffin, washed to remove the paraffin and added to a glutaraldehyde solution. US-A-2704269 relates to the preparation of glycerinated gelatin and solutions of gelatin in polyhydric alcohols. Gelatin and glycerin are mixed together and heated to a temperature of from 80-100°C. SUMMARY OF THE INVENTION The present invention relates to pharmaceutical compositions suitable for implantation into the periodontal crevice and capable of treating periodontal or other disease. In detail, the invention comprises a solidified pharmaceutical composition for permitting the sustained release of a pharmacological agent which comprises a polymeric matrix containing a plasticizing agent, and the pharmacological agent, wherein the polymeric matrix comprises a cross-linked, water-insoluble protein and a cross-linking agent. DESCRIPTION OF THE PREFERRED EMBODIMENTS The sustained-release pharmaceutical compositions of the present invention are polymeric films capable of being inserted into the gingival crevice. As used herein, the terms "device," "implant," "sustained release composition," and "compositions," are intended to be equivalent and to refer to essentially film-like materials suitable for insertion and retention in the periodontal cavity. The term "gingival crevice" is meant to be equivalent to the terms "periodontal crevice," "periodontal cavity," or "periodontal pocket." As such, the term is intended to refer to the space between the tooth and gum of an individual. The nature of the preferred components of the pharmaceutical compositions of the present invention are described in greater detail below. I. THE COMPONENTS OF THE PHARMACEUTICAL COMPOSITIONS OF THE PRESENT INVENTION A. THE POLYMERIC MATERIAL OF THE COMPOSITION In order to provide a biodegradable polymeric matrix for sustained drug release, it is preferable to employ a polymeric matrix composed of cross-linked protein. Suitable polymers include proteins derived from connective tissue (such as gelatin and collagen), albumin proteins (such as serum albumin, milk albumin, soy albumin, etc.), enzymes (such as papain, chymotrypsin, etc.), serum proteins (such as fibrinogen), and the proteolytic degradation products of bacterial, plant, or animal cells (i.e., tryptone, peptone, etc.). It is not necessary to employ a single protein; thus, the compositions of the present invention may contain two or more different proteins. The present invention does not require the use of protein having a specific level of purity. Thus, protein of any grade of purity may be employed. It is, however, preferable to employ protein having a high degree of purity, and especially preferable to employ protein having a defined (i.e., specifiable) composition, since the use of such proteins increases the degree with which the release of the pharmaceutical agent may be controlled. Thus, it is more preferable to employ a protein such as gelatin or albumin, than a proteolytic degradation product such as tryptone. Although any of a variety of proteins may be employed, it is preferable to employ gelatin, and most preferable to employ a gelatin which has been partially hydrolyzed by enzymatic action. The molecular weight of the preferred partially hydrolyzed gelatin is preferably between 1,000-12,000 d. Byco R proteins (a registered trademark of Croda Colloids, Ltd.) and in particular Byco R E.C.A. and O. have been found to be the most preferred proteins for use as the polymeric matrix of the present invention. The molecular weights of these proteins range from about 7,600 to about 50,000 d. B. THE CROSS-LINKING AGENT OF THE COMPOSITIONS To be effective in treating (i.e., reversing the progress of, or eliminating) a disease such as periodontal disease, it is necessary that the drug-releasing compositions of the present invention be maintained for a prolonged period of time (i.e., 2-10 days). Since the above-described polymeric materials are water-soluble, they will, if unaltered, dissolve too rapidly to provide an effective therapy for a disease such as periodontal disease. To render such compositions suitable for use in the present invention, it is desirable to treat the compositions in a manner which will make them water-insoluble. Any means capable of accomplishing this goal may be employed; however, it is preferable to employ an agent which is capable of cross-linking protein chains. Suitable cross-linking agents include aldehydes (such as formaldehyde, glutaraldehyde, etc.), alcohols, di-, tri-, or tetravalent ions (such as aluminum, chromium, titanium, or zirconium ions), acyl chlorides (such as sepacoyl chloride, tetraphthaloyl chloride), or agents such as bis-diazobenzidine, phenol-2,4-disulfonyl chloride, 1,5-difluoro-2,4-dinitrobenzene, urea, 3,6-bis(mercurimethyl)-dioxane urea, dimethyl adipimidate, N,N′-ethylen-bis-(iodoacetamide). In addition to the above-described chemical agents, any physical means capable of producing cross-links in proteins may alternatively be employed. Such means include heat, pressure, or radiation. The type and the amount of cross-linking agent will control both the rate of release of the drug and the rate of degradation of the device. Thus, increasing the extent of cross-linking increases the duration of the implant and decreases the rate of drug release. Since the cross-linked protein polymer is no longer water-soluble, its degradation is mediated by the proteolytic activity of enzymes normally present in the gingival crevice fluid and/or by chemical degradation. C. THE PLASTICIZING AGENT OF THE SUSTAINED-RELEASE COMPOSITIONS To improve the flexibility of the sustained-release device, a plasticizing agent is added. Examples of suitable plasticizing agents include phthalate esters, phosphate esters, glycol derivatives, hydrocarbons, oils, or fatty acids. Glycerin and sorbitol have been found to be preferred plasticizing agents. The most preferred plasticizing agent is glycerin. The type and amount of plasticizing agent incorporated into the composition will control the flexibility of the implant film. D. THE PHARMACOLOGICAL AGENT OF THE COMPOSITIONS A large variety of pharmacological agents may be incorporated into the compositions of the present invention. Generally, the amount of drug necessary to obtain the desired therapeutic effect will vary, depending upon the particular drug used and its therapeutic usage. Suitable drugs which can be administered using the sustained drug release compositions of the present invention include drugs belonging to the following groups of therapeutic agents: diuretics, e.g., benzthiazide, chlorothiazide, hydrochlorothiazide, cyclothiazide, flumethiazide, furosemide, thiamterene, ethacrynic acid and bumetanide; sedatives and hypnotics, e.g., barbiturates such as phenobarbital, sodium phenobarbital, and the like; chloral hydrate; glutethimide and methylprylon methaqualone; tranquilizers, such as chloropromazine, promazine, prochlorperazine, reserpine, meprobamate, benzodiazepines, such as chlordiazepoxide, diazepam, oxazepam and bromazepam; antibiotics such as penicillins, cephalosporins, tetracyclines, oxytetracyclines, chlorotetracycline, metronidazole, chloramphenicol and streptomycin; antibacterials such as sulfonamides, phenolics, mercurials, quarternary ammonium compounds and chlorhexidine; analgesics such as codeine, morphine, meperidine, phenazocime, propoxyphene and pentazocine; antipyretics and anti-inflammatory agents, such as aspirin, salicylamide, naproxen, indomethacin, fenoprofen, indoprofen, diclofenac and carprofen; anti-tumor agents such as 5-fluorouracil, floxuridine, cyclophosphamide, estramustine phosphate cytosine and arabinoside; cardiovascular drugs, such as nitroglycerin, amyl nitrite, pentaerythritol tetranitrate, isosorbide dinitrate, pyridamole, propranolol, digitalis, digitoxin and digoxin; anti-arrhythmic drugs such as quinidine, lidocaine, procainamide and disopyramide; hypotensive drugs such as hydralazine; anticonvulsants such as phenytoin, methsuximide, phenazepam, carbamazepine, ethotoin and clonopin and; anti-ulcer drugs such as cimetidine and tranitidine; and hypoglycemic drugs such as the thiazides. II. FORMULATION OF THE SUSTAINED-RELEASE DRUG DELIVERY IMPLANTS OF THE PRESENT INVENTION It is possible to mix the above-described components in any ratio which is capable of producing a solution which, when dried, forms a long-lasting, physiologically acceptable implant. The desired characteristics of such an implant include flexibility, biodegradability, sustained retention, and the capacity to permit the diffusion of a therapeutically active agent. The components of the sustained-release drug delivery implants may be mixed as liquids, or as solids to be dissolved in a suitable solvent. Especially suitable solvents include water, ethanol, and water-ethanol mixtures. It is preferable to prepare the sustained-drug release compositions of the present invention by pouring a liquid form of the present invention into molds which may be dried into large film-like sheets. These sheets may then be cut to the desired implant size. If the concentration of protein used in the compositions is too high, it will affect the pourability of the solution. If the protein concentration is too low, the release rate of the sustained-release composition will be too rapid. This excessive drug release rate may, however, be lowered through the use of lower concentrations of the pharmacological agent. It is, therefore, preferable to employ a protein concentration range which results in the formation of a solution having acceptable pourability, but which, when dried into a film-like material, is capable of releasing a pharmacological agent over a sustained period of time. When dried to produce the implants of the present invention, such compositions must have a high enough concentration of protein to produce a non-gel-like film having structural stability. Such suitable compositions can be formulated from a liquid which contains from 10-50% (by weight) protein. Upon evaporation of about 90% of solvent, such compositions would contain of from 16% to 91% (w/w) protein. It is preferable that the solidified composition have a flexibility of from 0.1 kg/mm² to 50 kg/mm². The plasticizer which is added to the above-described solution to control the flexibility of the final dried film implant, must be present in an amount sufficient to prevent the final film from being brittle, or too flexible. The plasticiser must not be present in an amount which prevents the release of the pharmacological agent. Thus, such a plasticiser should be present between of from 0.01% to 15% (w/w) prior to the drying of the compositions. Upon evaporation of about 90% of solvent, such compositions would contain of from 0.010% to 41% (w/w) plasticizing agent. The pharmacological agent of the composition may be added to the implant by any of several processes. In one embodiment, a powder form of the pharmacological agent is introduced into the compositions (which are in liquid form) and permitted to dissolve in situ . In a second embodiment, the pharmacological agent is dissolved in a suitable solvent prior to its addition to a liquid form of the composition. In yet another embodiment, a liquified form of the pharmacological agent is introduced into a solidified implant. Such introduction may be accomplished by immersing the solidified implant in a solution which contains the pharmacological agent, or by placing a suitable amount of the pharmacological agent in contact with the solidified implant and permitting the implant to absorb the pharmacological agent. The amount of the pharmacological agent added to the implant will vary, in a manner understood by those of ordinary skill in the art, depending upon such criteria as: (1) the desired total dosage, (2) the desired release kinetics, (3) the desired duration of treatment, (4) the desired size of the implant and its intended location, or (5) possible interactions between the pharmaceutical agent of the implant and any other medicament being administered. The above criteria will depend upon such factors as the patient's age, height, weight, sex, medical history, etc. The pharmacological agent must be present in an amount sufficient to impart therapeutic effect to the pharmaceutical composition. The nature of the active agent in the film also plays an important role in the control release mechanism. A film containing 20% w/w of chlorhexidine acetate per protein has been found to release the agent more slowly than the same film containing 20% w/w of tetracycline HCl. Different salts of the same active agent are released at different rates. For example, chlorhexidine acetate has been found to be released more slowly than chlorhexidine HCl from films having the same formulation and containing 20% (w/w) chlorhexidine per protein. In general, the concentration of pharmacological agent will vary from 0.01 mg-2 g per therapeutic treatment. The pharmaceutical compositions (when in liquid form) will, in general, contain between 0.01-25% pharmacological agent (by weight). Upon evaporation of approximately 90% of the liquid solvent, the resulting film-like implant will contain between approximately 0.013-61% pharmacological agent (by weight). The implants of the present invention may contain only a single pharmacological agent or may contain a combination of two or more pharmacological agents. For example, an implant used in the treatment of periodontal disease may contain several antimicrobial agents or may contain both (i) (one or more) antimicrobial agent(s) and (ii) an analgesic and/or an anti-inflammatory agent. In a preferred embodiment, the weight ratios of pharmacological agent to protein in the films will vary from 0.01:7 (respectively) to 3:1 (respectively). In a preferred embodiment, the weight ratio of plasticizing agent to protein will vary from 0.01:7 (respectively) to 4:7 (respectively). When a cross-linking agent is to be added to the non-evaporated liquid form of the composition, it should be present in an amount capable of rendering the protein polymer water-insoluble. If, however, excessive amounts of the cross-linking agent are introduced, the resulting implant will have an unacceptably slow drug release rate. Thus, if a cross-linking agent is provided to the composition in liquid form (prior to the formation of the film-like solid implants), it should be provided in an amount sufficient to render the resulting implant insoluble, but not in an amount which prevents the release of the pharmacological agent from the pharmaceutical composition. The action of the cross-linking agent may result in the denaturation of the protein. The degree of denaturation of the protein caused by the cross-linking agent provides a means of controlling the degradability of the films in vivo and in vitro , there being an inverse relationship between the degree of denaturation and the degradability of the film. The release of the pharmacological agents from the films can be manipulated by the degree of cross-linking and denaturation of the protein, there being a direct relationship between the degree of cross-linking or denaturation and the rate of release of the active agent from the film. In general, if one desires to add a cross-linking agent to the composition prior to its drying into the desired film-like material, the cross-linking agent should be added to the liquid in an amount of from 0.0001% to 5% (weight by weight). Upon evaporation of about 90% of solvent, the resulting film would contain from 0.0001% to 22% (weight by weight) cross-linking agent. Although, as described above, it is possible to incorporate a cross-linking agent into a liquid solution which, upon drying, forms the film-like implants of the present invention, it is also possible to additionally dry the liquid compositions, and to than cross-link the protein polymer films. The most preferable way of cross-linking is a combination of the method where a partially cross-linked film is further incubated in the presence of glutaraldehyde vapors. Such treatment is preferable, since it minimizes the time necessary to attain sufficient cross-linking. Sufficient cross-linking is considered to have been achieved when the final, film-like implant cannot be dissolved in water within 10 days. The amount of the cross-linking agent which is ultimately incorporated into an implant treated in the above-described manner is extremely small, and results in almost no change in weight. Any means capable of solidifying the liquid compositions of the present invention may be employed. Thus, solidification may be accomplished by evaporating solvent until a desired degree of rigidity is obtained. This evaporation may be accomplished by incubating the liquid compositions at ambient or elevated temperatures, either at atmospheric pressure or in vacuo . Evaporation which occurs in the presence of elevated temperatures, or in vacuo , may result in surface defects (such as air pockets, etc.). Thus, if such defects are undesirable, it is preferable to dry the liquid compositions at ambient temperatures under atmospheric pressure. It is most preferable to form the implants of the present invention by evaporating a liquid form of the composition into a solidified film-like material. Such evaporation is most preferably conducted at room termperature or temperatures between 40-50°C, at atmospheric pressure. The above-described evaporation process removes a substantial amount of the solvent initially present in the liquid composition. The film is, however, not completely solvent-free. Thus, in a preferred embodiment in which the solvent is water or a water-ethanol mixture, the film is hydrated and non-anhydrous. in general, it is desirable to evaporate sufficient solvent to produce a film-like solid, but not so much solvent as to impair the flexibility of the resulting film. Thus, in general, it is desirable to evaporate between 70-95% of the solvent initially present in the liquid compositions. It is most preferable that the obtained film will contain from 7.5% to 17.5% w/w of solvent. The evaporation of solvent results in a loss of both weight and volume, and thus alters the concentration percentages of the components of the pharmaceutical composition. The effect of evaporation on the concentration of components is shown in Table 1. In order to be inserted into a patient's periodontal pocket to treat periodontal or other disease, the implant should preferably have a thickness which ranges from 0.01-0.5 millimeters, and preferably have a thickness of between 0.1 and 0.3 millimeters. In order to be inserted in the periodontal pocket, it is preferable that the implant shape be oval. Although the width and length of the implant may vary depending upon the size of the periodontal pocket of the recipient patient, it is preferable to use implants having a width of between 1-5 millimeters, and preferably between 2-4 millimeters. It is preferable to employ implants having a length of between 3-10 millimeters, and most preferable to employ implants having a length of between 5-8 millimeters. Implants having such dimensions, and, therefore, suitable for insertion into the periodontal pocket of a patient may be employed to treat or prevent periodontal disease (as by containing an anti-microbial agent, etc.). Alternatively, such implants may be used to provide a pharmacological agent unrelated to periodontal disease to a recipient patient. In such an embodiment, the periodontal pocket is employed as a convenient site into which the sustained release implant of the invention may be inserted. The implant may be used to provide any of the large variety of pharmacological agents whose prolonged release may be desired in the treatment of disease. It is alternatively possible to prepare an implant of greater thickness or of different dimensions which will not be inserted into the periodontal cavity. The size and shape of such an implant will depend upon (a) the dimensions of the site into which it is to be inserted, (b) the desired duration of therapy, (c) the desired amount and concentration of the pharmacological agent which it contains or (d) the desired drug release kinetics. Such implants may be used to provide sustained drug release for any of a variety of diseases or conditions. Implants may be used to treat (or prevent) microbial infections at wounds (either accidental or as a consequence of surgery or other medical treatments), burns, abrasions, etc. Such implants may be used alone, in combination with bandages or dressings, or as an adjunct to other treatments. Implants that contain antitumor agents may be placed at the site of the tumor, thereby providing a therapy for cancer. Implants containing analgesics or antipyretics could be used to alleviate pain or inflammation Implants containing cardiovascular drugs or anti-arrhythmic drugs may be used in the treatment of heart disease. In a similar manner, by employing implants which contain a suitable pharmacological agent, it is possible to provide effective therapy for the large variety of diseases that may be treated by a sustained drug therapy regime. The implants of the present invention may be individually produced, or may be cut from a larger film-like sheet. When employing Byco R as the protein polymer, it is preferable to prepare a liquid composition which contains of from 2% to 6% by weight of the pharmacological agent (preferably chlorhexidine), of from 2% to 5% plasticising agent (preferably glycerin), of from 15% to 30% Byco R protein and of from 0.0006% to 0.13% of cross-linking agent preferably glutaraldehyde. It is preferable to dry such a composition by evaporating the solvent to produce a film of from 7.5% to 17.5% w/w of solvent and from 48% to 83% w/w of cross-linked Byco R and from 3.8% to 21% w/w of plasticiser agent and from 4% to 24% w/w of pharmaceutical agent. This film-like material is then incubated in the presence of a cross-linking agent (preferably glutaraldehyde) until a sufficient degree of cross-linking has been obtained. Having now generally described this invention, the same will be better understood by reference to certain specific examples which are included herein for purposes of illustration only and are not intended to be limiting of the invention, unless specified. Sustained pharmaceutical implants were prepared according to the procedures described in the following examples. COMPARATIVE EXAMPLE 1 1. 9.75 g of Byco E was dissolved in distilled water to make 26 g and allowed to stand. 2. 1.5 g of chlorhexidine acetate was solubilized in 5 ml of absolute ethanol. 3. 20 g of the clear Byco® solution was added to the chlorhexidine solution while stirring constantly. 4. 1.0 g of glycerine was added to the solution while stirring constantly. 5. 5 g of the liquid was poured into plastic petri dishes (9.5 cm in diameter). 6. The petri dishes were placed in an evaporator for 48 hours and the liquid was allowed to evaporate. EXAMPLE 2 1. 9.75 g of Byco® E was dissolved in distilled water to make 26 g and allowed to stand. 2. 1.5 g of chlorhexidine acetate was solubilized in 5 ml of absolute ethanol. 3. 20 g of the clear Byco solution was added to the chlorhexidine solution, while stirring constantly. 4. 1.0 g of glycerine was added to the solution while stirring constantly. 5. 50 µl of formaldehyde solution was added slowly to 5 g of the liquid. 6. The liquid was poured into plastic petri dishes (9.5 cm in diameter). 7. The petri dishes were placed in an evaporator for 48 hours and the liquid was allowed to evaporate. EXAMPLE 3 1. 9.75 g of Byco® E was dissolved in distilled water to make 26 g and allowed to stand. 2. 1.5 g of chlorhexidine acetate was solubilized in 5 ml of absolute alcohol. 3. 20 g of the clear Byco solution was added to the chlorhexidine solution while stirring constantly. 4. 1.0 g of glycerine was added to the solution while stirring constantly. 5. 100 µl of formaldehyde solution was added slowly to 5 g of the liquid. 6. The liquid was poured into plastic petri dishes (9.5 cm in diameter). 7. The petri dishes were placed in an evaporator for 48 hours and the liquid was allowed to evaporate. EXAMPLE 4 1. 9.75 g of Byco E was dissolved in distilled water to make 26 g and allowed to stand. 2. 1.5 g of chlorhexidine acetate was solubilized in 5 ml of absolute alcohol. 3. 20 g of the clear Byco solution was added to the chlorhexidine solution while stirring constantly. 4. 1.0 g of glycerine was added to the solution while stirring constantly. 5. 150 µl of formaldehyde solution was added slowly to 5 g of the liquid. 6. The liquid was poured into plastic petri dishes (9.5 cm in diameter). 7. The petri dishes were placed in an evaporator for 48 hours and the liquid was allowed to evaporate. EXAMPLE 5 1. 9.75 g of Byco® E was dissolved in distilled water to make 26 g and allowed to stand. 2. 1.5 g of chlorhexidine acetate was solubilized in 5 ml of absolute ethanol. 3. 20 g of the clear Byco® solution was added to the chlorhexidine solution while stirring constantly. 4. 1.0 g of glycerine was added to the solution while stirring constantly. 5. 200 µl of formaldehyde solution was added slowly to 5 g of the liquid. 6. The liquid was poured into plastic petri dishes (9.5 cm in diameter). 7. The petri dishes were placed in an evaporator for 48 hours and the liquid was allowed to evaporate. The following examples were prepared using the same procedure as that described above -- amounts are in grams unless indicated otherwise and refer to the liquid compositions. EXAMPLE 19 Byco® E 7.5 Water ad 25 Sorbitol 1.5 Chlorhexidine acetate 1.5/5 ml ethanol Formaldehyde 200 µl/5 g Sustained pharmaceutical implants were prepared according to the procedures described in the following examples. COMPARATIVE EXAMPLE 20 1. 7.5 g of gelatin were dissolved in 39.0 ml of hot distilled water. 2. 0.75 g of chlorhexidine acetate was solubilized in 5.0 ml of ethyl alcohol. 3. The alcohol solution was added to the aqueous solution. 4. 5 g of the liquid was poured into petri dishes, diameter 9.5 cm. 5. The petri dishes were placed in an evaporator for 48 hours and the liquid was allowed to evaporate. COMPARATIVE EXAMPLE 21 1. 7.5 g of gelatin were dissolved in 39.0 ml of hot distilled water. 2. 0.75 g of chlorhexidine acetate was solubilized in 5.0 ml of ethyl alcohol. 3. The alcohol solution was added to the aqueous solution. 4. 50 µl of formaldehyde was added slowly to 5 g of the liquid. 5. The liquid was poured into petri dishes (9.5 cm in diameter). 6. The petri dishes were placed in an evaporator for 48 hours and the liquid was allowed to evaporate. COMPARATIVE EXAMPLE 22 1. 7.5 g of gelatin were dissolved in 39.0 ml of hot distilled water. 2. 0.75 g of chlorhexidine acetate was solubilized in 5.0 ml of ethyl alcohol. 3. The alcohol solution was added to the aqueous solution. 4. 100 µl of formaldehyde was added slowly to 5 g of the liquid. 5. The liquid was poured into petri dishes (9.5 cm in diameter). 6. The petri dishes were placed in an evaporator for 48 hours and the liquid was allowed to evaporate. EXAMPLE 23 In vitro release tests Films were prepared by evaporating approximately 80% of the solvent from the compositions of the preceding examples. The casted films were carefully cut into squares of 1 x 1 cm dimension. The thickness of each film was measured in five different places on the film, using a micrometer gauge. The average thickness of the films was 200 microns. The films were placed in distilled water at 37°C with constant shaking at 100 rpm. The solutions were circulated through a flow cell of a U.V. spectrophotometer, using a peristaltic pump. The amount of active ingredient released from the film was measured at 254 nm for chlorhexidine protein or at 275 nm for tetracycline or tetracycline HCl. The results of this experiment are shown in Tables 2-5. EXAMPLE 24 INHIBITION OF ORAL BACTERIAL GROWTH IN VITRO Films were prepared using the compositions of Examples 1-4. The films were cut into circles and placed on Isosensitest agar plates seeded with the oral bacteria Streptococcus mutans . After incubating at 37°C for 24 hours, the films were removed from the agar plates and placed on fresh plates seeded with Streptococcus mutans and incubated further for 24 hours. This procedure was repeated until no inhibition of bacterial growth was observed. The area of inhibition of growth around the films was measured. The results of this experiment are shown in Table 6. EXAMPLE 25 A sustained release composition composed of chlorhexidine and Byco E protein and suitable for use as a periodontal implant was prepared in a preferred manner by incubating the non- or the partially cross-linked films in the presence of a vapor containing a cross-linking agent. Films prepared in such a manner can be considered to have the following eight stages: Stages in the Formation of the Film 1. Byco E is dispersed into a solution. 2. The solution is allowed to clear. 3. Chlorhexidine acetate is added to 5 ml of ethanol supplemented with glycerine. The solution is mixed for 10 minutes. 4. The Byco solution and the chlorhexidine solution are mixed together at 35°C for 10 minutes. 5. Glutaraldehyde is added to 6.0 g of the above solution. 6. The mixture is poured into molds. 7. The solvent is allowed to evaporate from the mixture, thus forming a thin film. 8. The obtained film is placed in an atmosphere of glutaraldehyde vapor. In producing the above film, the following considerations were made at the indicated stages: Stage 1 a. The range of Byco® protein in the solution is 10%-60% w/w. b. The Byco® is dissolved in bidistilled water, buffered to pH range of 3.0-9.0. c. Rose bengal is added to the solution concentration of 0.00001-1 mg/ml. Stage 3 a. 0-6.0 g of chlorhexidine acetate or chlorhexidine is solubilized in ethanol. b. The active ingredient, e.g., chlorhexidine or its salts, was added to the Byco® solution in the form of a solid powder. Stage 7 The solvent is evaporated at a range of temperature of 20°C-60°C. Stage 8 The obtained films are placed in an atmosphere of glutaraldehyde for 0-72 hours at a range of temperature of 20°C-60°C. Characteristics of the obtained film: 1. Concentration of water: 5-30% W/W 2. Concentration of cross-linked Byco®: 14-95% w/w 3. Concentration of chlorhexidine or chlorhexidine acetate: 0-66% w/w 4. Concentration of glycerin: 0-52% w/w EXAMPLE 26 The steps of a preferred method for producing the periodontal implant of the present example are provided below: 1. 7.5 g Byco® E was dispersed in a bidistilled water to make 22.0 g. 2. The mixture was allowed to clear. 3. 1.5 g of chlorhexidine acetate was added to 5 ml of ethanol absolute, supplemented with 1.3 g glycerine. The solution was mixed for 10 minutes. 4. The Byco® and chlorhexidine solutions were mixed together at 35°C for 10 minutes. 5. 300 µl of glutaraldehyde was added to 5.0 g of the above solution. 6. The mixture was poured into molds. 7. The solvent was allowed to evaporate at room temperature for 48 hours while forming a film. 8. The above-obtained film was placed in an atmosphere of glutaraldehyde vapor for 24 hours. The obtained films had the following approximate concentrations: 1. concentration of water : 10% 2. concentration of Byco® : 66% 3. Concentration of Chlorhexidine or chlorhexidine acetate : 13% 4. concentration of glycerin : 11% EXAMPLE 27 Periodontal implants having various proportions of ingredients were prepared in accordance with the procedure of Example 25. The amounts and ingredients used to produce these implants are shown in Table 7. EXAMPLE 28 The in vitro drug release profile of four of the implants produced in Example 25 were determined. The release profiles are presented in Table 8. COMPARATIVE EXAMPLE 29 CLINICAL TRIALS Preliminary clinical trials were conducted on patients with periodontal diseases. Films prepared using the compositions of Comparative Example 1 and Example 2, 3 or 4 were inserted into periodontal pockets of volunteers in order to test the rate of degradation. Films prepared using the compositions disclosed in Comparative Example 1 degraded inside the periodontal pocket within four hours. Films prepared using the compositions disclosed in Examples 2 and 3 degraded within 20 hours. The film prepared from the composition of Example 4 degraded within approximately 36 hours. Further tests were conducted on the effect of degradable films on the microflora of periodontal pockets. Preliminary clinical studies have shown that there is a sharp decrease in the number of motile bacteria including spirochetes in the periodontal pocket, after treatment with the film. A reduction in the total count of anaerobic bacteria was observed, accompanied by a reduction in the black pigmented Bacteriodes. Films prepared from the composition of Example 5 were inserted into periodontal pockets. Samples of subgingival flora were taken before and after the treatment. The samples were examined by using Dark Field Microscopy. It was found that after treatment with these films, there was a reduction in the number of motile bacteria. In three pockets, there was 100% decrease in the number of motile bacteria while in another two pockets there was a 75% reduction in the motile bacteria. As will be realized from the above description and results, the controlled release of an active antibacterial agent into the periodontal pocket is a prefered way of treating periodontal diseases. The local placement of a device which provides the controlled release of an active agent from a degradable matrix minimizes the need for removal of the device from the periodontal pockets, when the treatment period is over. This minimizes the number of visits to the periodontist as well as the discomfort associated with the removal of the film. It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative examples and it is therefore desired that the present embodiments and examples be considered in all respects as illustrative and not restrictive, reference being made to the appended claims, rather than to the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims: Claims for the following Contracting States : BE, CH, DE, FR, GB, IT, LI, LU, NL, SE A pharmaceutical composition for permitting the sustained release of a pharmacological agent which comprises a polymeric matrix containing a plasticising agent, a pharmacological agent, a cross-linking agent and a cross-linked water-insoluble protein, where the water-insoluble protein has been formed by cross-linking a water-soluble protein with the cross-linking agent. A pharmaceutical composition as claimed in claim 1 which is a film containing the cross-linking agent in an amount of from 0.0001% to 22% by weight. A composition as claimed in claim 1 or 2 wherein said cross-linking agent is present in an amount of from 0.01% to 26%. A pharmaceutical composition according to any of claims 1 to 3 wherein said protein is present at a concentration of from 14% to 93%. A pharmaceutical composition according to any of the preceding claims wherein said plasticizing agent is present at a concentration of from 0.01% to 52%. A pharmaceutical composition according to any of the preceding claims wherein said composition is a film having a thickness of from 0.01 to 0.5mm. A pharmaceutical composition according to any of the preceding claims wherein said pharmacological agent and said protein are present at a relative weight ratio which ranges from 0.01:7 to 3:1. A pharmaceutical composition according to any of the preceding claims, wherein said plasticizing agent and said protein are present at a relative weight ratio which ranges from 0.01:7 to 4:7. A pharmaceutical composition according to any of the preceding claims, wherein said composition has a flexibility which ranges from 0.1 kg/mm² to 50 kg/mm². A liquid composition suitable for the preparation of a pharmaceutical composition for permitting the sustained release of a pharmacological agent which comprises a polymeric matrix, the liquid composition comprising a plasticizing agent, a pharmacological agent, a cross-linking agent and a cross-linkable water-soluble protein, where the cross-linking agent is adapted to cross-link the water-soluble protein to form a cross-linked water-insoluble protein. A composition as claimed in any of of claims 1 to 10 wherein said cross-linked protein is additionally cross-linked by incubation in the presence of cross-linking means, said means being selected from the group consisting of: heat, pressure or radiation. A composition as claimed in any of claims 1 to 11 wherein said cross-linking agent is selected from the group consisting of: aldehydes, alcohols, divalent ions, trivalent ions, tetravalent ions, acyl chlorides, bis-diazobenzidine, phenol-2,4-disulphonyl chloride, 1, 5 -difluoro-2, 4-dinitrobenzene, urea, 3, 6-bis(mercurimethyl)-dioxane urea, dimethyl adipimidate, and N,N'-ethylen-bis-(iodo-acetamide). A composition as claimed in any of claims 1 to 12 wherein said cross-linking agent is an aldehyde selected from the group consisting of formaldehyde and glutaraldehyde. A composition as claimed in claim 13 wherein said cross-linking agent is glutaraldehyde. A composition according to any of the preceding claims wherein said protein is selected from the group consisting of: gelatin, collagen, albumin, an enzyme, and fibrinogen. A composition according to any of the preceding claims wherein said protein is gelatin. A composition according to any of the preceding claims wherein the protein is hydrolyzed gelatin. A composition according to any of the preceding claims wherein said plasticizing agent is selected from the group consisting of: a phthalate ester, a phosphate ester, a glycol derivative, a hydrocarbon, an oil, and a fatty acid. A composition according to any of the preceding claims wherein said plasticizing agent is a glycol derivative. A composition according to any of the preceding claims wherein the plasticising agent is selected from the group consisting of: glycerin and sorbitol. A composition according to any of the preceding claims which contains one or more than one pharmacological agent selected from the group consisting of: a diuretic, a sedative, a hypnotic, a tranquilizer, an antibiotic, an antibacterial, an analgesic, an antipyretic, an anti-tumor agent, a cardiovascular drug, an anti-arrthymic drug, a hypotensive drug, an anti-ulcer drug, and a hypoglycemic drug, or consists of only one or more than one of the said group. A composition according to any of claims 11 to 21 wherein said pharmacological agent is an antibacterial agent. A composition according to claim 22 wherein said antibacterial agent is selected from the group consisting of penicillin, cephalosporin, tetracycline, oxytetracycline, chlortetracycline, metronidazole, chloramphenicol, streptomycin, neomycin, a sulfonamide, a phenolic compound, a mercurial, a quarternary ammonium compound, and chlorhexidine. A pharmaceutical composition according to claim 23 wherein said antibacterial agent is chlorhexidine. A composition according to claim 24 wherein said film is from 3 to 10 mm in length, and from 1 to 5 mm in width, and from 0.01 to 0.5 mm in depth. The use of a composition as claimed in any of claims 1 to 9 and any of claims 11 to 25 when dependent upon claims 1 to 9 in the preparation of a pharmaceutical agent for providing sustained release of a pharmacological agent for use in human or veterinary medicine. The use of a composition as claimed in any of claims 1 to 9 and any of claims 11 to 25 when dependent upon claims 1 to 9 in the preparation of a pharmaceutical agent for providing sustained release of a pharmacological agent for use in therapy of periodontal disease. The use of a composition as claimed in any of claims 1 to 9 and any of claims 11 to 25 when dependent upon claims 1 to 9 in the preparation of a pharmaceutical agent for providing sustained release of a pharmacological agent in the form of an implant adapted for insertion into a periodontal pocket of a patient. A process for the preparation of a pharmaceutical composition, the process comprising causing or allowing the cross-linking agent in a liquid composition according to any of the claims 10 to 25 to cross-link the water-soluble protein to form a composition according to any of claims 1 to 9 and any of claims 11 to 25 when dependent upon claims 1 to 9. Claims for the following Contracting States : AT, ES, GR A process for making a pharmaceutical composition for permitting the sustained release of a pharmacological agent the process comprising providing a matrix of material containing a plasticizing agent, a cross-linking agent and the pharmacological agent, the material of the matrix comprising a water-soluble protein adapted on cross-linking to afford a polymeric matrix of cross-linked water insoluble protein, and cross-linking the water-soluble protein into a water-insoluble protein. A process according to claim 1 wherein said cross-linked protein is additionally cross-linked by incubation in the presence of cross-linking means, said means being selected from the group consisting of: heat, pressure or radiation. A process according to claim 1 or 2 wherein said cross-linking agent is selected from the group consisting of: aldehydes, alcohols, divalent ions, trivalent ions, tetravalent ions, acyl chlorides, bis-diazobenzidine, phenol-2,4-disulfonyl chloride, 1, 5 -difluoro-2, 4 -dinitrobenzene, urea, 3,6-bis(mercurimethyl)-dioxane urea, dimethyl adipimidate, and N,N'-ethylene-bis-(iodo-acetamide). A process as claimed in any of claims 1 to 3 wherein the composition is a film containing the cross-linking agent in an amount of from 0.0001% to 22% by weight. A process as claimed in any of claims 1 to 3 wherein said cross-linking agent is present in said composition in an amount of from 0.01% to 26%. A process as claimed in any of claims 1 to 5 wherein said cross-linking agent is an aldehyde selected from the group consisting of formaldehyde and glutaraldehyde. A process according to any of the preceding claims wherein said cross-linking agent is glutaraldehyde. A process of any of the preceding claims wherein said protein is selected from the group consisting of: gelatin, collagen, albumin, an enzyme, and fibrinogen. A process according to any of the preceding claims wherein said protein is gelatin. A process according to claim 9 wherein said gelatin is hydrolyzed gelatin. A process according to any of the preceding claims wherein said protein is present at a concentration of from 14% to 93°. A process according to any of the preceding claims wherein said plasticizing agent is selected from the group consisting of: a phthalate ester, a phosphate ester, a glycol derivative, a hydrocarbon, an oil, and a fatty acid. A process according to claim 12 wherein said plasticizing agent is a glycol derivative. A process according to claim 17 wherein said glycol derivative is selected from the group consisting of: glycerin and sorbitol. A process according to any of the preceding claims wherein said plasticizing agent is present at a concentration of from 0.01% to 52%. A process according to any of the preceding claims which contains one or more than one pharmacological agent selected from the group consisting of: a diuretic, a sedative, a hypnotic, a tranquilizer, an antibiotic, an antibacterial, an analgesic, an antipyretic, an anti-tumor agent, a cardiovascular drug, an anti-arrthymic drug, a hypotensive drug, an anti-ulcer drug, and a hypoglycemic drug, or consists of only one or more than one of the said group. A process according to claim 16 wherein said pharmacological agent is an antibacterial agent. A process according to claim 17 wherein said antibacterial agent is selected from the group consisting of penicillin, cephalosporin, tetracycline, oxytetracycline, chlortetracycline, metronidazole, chloramphenicol, streptomycin, neomycin, a sulfonamide, a phenolic compound, a mercurial, a quarternary ammonium compound, and chlorhexidine. A process according to claim 18 wherein said antibacterial agent is chlorhexidine. A process according to any of the preceding claims wherein said composition is a film having a thickness of from 0.01 to 0.5mm. A process according to claim 20 wherein said film is from 3 to 10 mm in length, and from 1 to 5 mm in width, and from 0.01 to 0.5 mm in depth. A process of any of the preceding claims wherein said pharmacological agent and said protein are present at a relative weight ratio which ranges from 0.01:7 to 3:1. A process according to any of the preceding claims, wherein said plasticizing agent and said protein are present at a relative weight ratio which ranges from 0.01:7 to 4:7. A pharmaceutical composition according to any of the preceding claims, wherein said composition has a flexibility which ranges from 0.1 kg/mm² to 50 kg/mm². The use of a product of a process as claimed in any one of the preceding claims in the preparation of an agent for providing sustained release of a pharmacological agent for use in human or veterinary medicine. The use of a product of a process as claimed in any one of the preceding claims in the preparation of an agent for providing sustained release of a pharmacological agent for use in therapy of periodontal disease. The use of a product of a process as claimed in any one of the preceding claims in the preparation of an agent for providing sustained release of a pharmacological agent in the form of an implant adapted for insertion into a periodontal pocket of a patient.

Inventors: FRIEDMAN,MICHAEL, SELA,MICHAEL, SOSKOLNE,AUBREY, STEINBERG,DORON
Applicants: YISSUM RESEARCH DEVELOPMENT COMPANY OF THE HEBREW UNIVERSITY OF JERUSALEM
Application year: 1987
Main classification: A61K9
IPC codes: A61K9, A61K47, A61P1