Compositions and methods for improved delivery of ionizable hydrophobic therapeutic agents

The present invention is directed to a pharmaceutical composition including a hydrophobic therapeutic agent having at least one ionizable functional group, and a carrier. The carrier includes an ionizing agent capable of ionizing the functional group, a surfactant, and optionally solubilizers, triglycerides, and neutralizing agents. The invention further relates to a method of preparing such compositions by providing a composition of an ionizable hydrophobic therapeutic agent, an ionizing agent, and a surfactant, and neutralizing a portion of the ionizing agent with a neutralizing agent. The compositions of the invention are particularly suitable for use in oral dosage forms.

FIELD OF THE INVENTION

The present invention relates to drug delivery systems, and in particular to pharmaceutical compositions for the improved delivery of ionizable hydrophobic compounds and methods therefor.

BACKGROUND

Hydrophobic therapeutic agents, i.e., therapeutic compounds having poor solubility in aqueous solution, present difficult problems in formulating such compounds for effective administration to patients. A well-designed formulation must, at a minimum, be capable of presenting a therapeutically effective amount of the hydrophobic compound to the desired absorption site, in an absorbable form. Even this minimal functionality is difficult to achieve when delivery of the hydrophobic therapeutic agent requires interaction with aqueous physiological environments, such as gastric fluids and intestinal fluids. Pharmaceutical compositions for delivery of such hydrophobic therapeutic agents must carry the hydrophobic compound through the aqueous environment, while maintaining the hydrophobic compound in an absorbable form, and avoiding the use of physiologically harmful solvents or excipients.

A number of approaches to formulating hydrophobic therapeutic agents for oral or parenteral delivery are known. Such approaches include, for example, formulations in which the hydrophobic therapeutic agent is present in an oil-in-water emulsion, a microemulsion, or a solution of micelles, liposomes, or other multi-lamellar carrier particles. While such approaches may be appropriate for some ionizable as well as non-ionizable hydrophobic therapeutic agents, they fail to take advantage of the unique acid-base chemical properties, and associated solubility properties, of ionizable compounds.

In particular, unlike non-ionizable hydrophobic therapeutic agents, ionizable hydrophobic therapeutic agents can be rendered soluble in aqueous solution if the pH of the solution is adjusted to ionize the therapeutic agent. Such an approach is well known in the art. For example, U.S. Pat. No. 5,773,029 is directed to a pharmaceutical composition of an acidic drug, wherein the solubility of the acidic drug is enhanced by simultaneous salt formation with an organic or inorganic base and complexation with a cyclodextrin. The resultant drug/cyclodextrin/base complexes reportedly are readily soluble in water in high concentrations.

U.S. Pat. No. 5,360,615 discloses a pharmaceutical carrier system for an acidic, basic or amphoteric pharmaceutical agent in which the pharmaceutical agent is partially ionized by an acid or base in a polyethylene glycol-based solvent system. The pharmaceutical agent reportedly shows enhanced solubility in the partially ionized form. The reference also discloses that addition of glycerin, propylene glycol and/or polyvinylpyrrolidone further enhances the solubility of the pharmaceutical agent in the polyethylene glycol base. However, the invention is limited to polyethylene glycol-based solvent systems and a narrow range of ionizing agent concentration, and there is no disclosure of other solvent systems. Thus, its utility is severely limited.

Similarly, U.S. Pat. No. 5,376,688 discloses a pharmaceutical solution of an acidic, basic or amphoteric pharmaceutical agent. The solution includes a pharmaceutical agent, an ionizing species, and a solvent system. The solvent system can be diethylene glycol monoethyl ether, glycerol caprylate/caprate, polyglycerol oleate, alpha-hydro-w-hydroxypoly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) block copolymers, or mixtures of those components. The solvent system can also be a mixture of polyethylene glycol and a polyoxyethylene sorbitan ester. Optional components include water, glycerin, propylene glycol, and polyvinylpyrrolidone. However, the invention is limited to these particular compounds and a narrow range of ionizing agent concentration, rendering its utility severely limited. Moreover, some of the solvent system components show poor or questionable biocompatibility, and thus would be impractical for drug delivery to a patient.

A further problem with conventional approaches to solubilizing ionizable hydrophobic therapeutic agents is the difficulty in maintaining the solubilized therapeutic agent in solubilized form. Thus, for example, while ionizing an acidic therapeutic agent with a base may increase its solubility, the therapeutic agent is prone to precipitation in the gastrointestinal tract due to the acidic pH conditions encountered upon administration to a patient, and the approximately 10 to 100-fold dilution expected in gastrointestinal or intestinal fluids. This precipitation is particularly disadvantageous, since the precipitated therapeutic agent is essentially unavailable for absorption, leading to difficulties in controlling dosages, and a need to administer large doses of the therapeutic agent to ensure that a therapeutically effective amount reaches the absorption site in a bioavailable form. Such difficulties necessarily result in increased costs, and compromised patient safety and therapeutic effectiveness.

Thus, there is a need for versatile and effective pharmaceutical compositions that overcome these deficiencies in the prior art.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide pharmaceutical compositions capable of solubilizing therapeutically effective amounts of ionizable hydrophobic therapeutic agents.

It is another object of the invention to provide pharmaceutical compositions capable of maintaining a solubilized ionizable hydrophobic therapeutic agent in solubilized form upon administration to a patient.

It is another object of the invention to provide pharmaceutical compositions of ionizable hydrophobic therapeutic agents with improved delivery of the therapeutic agent to the absorption site.

It is a further object of the invention to provide improved methods of preparing pharmaceutical compositions of ionizable hydrophobic therapeutic agents.

It is still another object of the invention to provide methods of treating an animal with pharmaceutical compositions of ionizable hydrophobic therapeutic agents.

In accordance with these and other objects and features, the present invention provides pharmaceutical compositions and methods for improved delivery of ionizable hydrophobic therapeutic agents.

In one embodiment, the invention is directed to a pharmaceutical composition including an ionizable hydrophobic therapeutic agent and a carrier. The carrier includes an ionizing agent to ionize the therapeutic agent, and a surfactant. Optionally, the carrier also includes solubilizers, triglycerides and neutralizing agents.

In another embodiment, the invention is directed to a pharmaceutical composition including a hydrophobic therapeutic agent having at least one ionizable functional group, and a carrier. The carrier includes an ionizing agent capable of ionizing the functional group, a surfactant, and a triglyceride.

In another embodiment, the invention is directed to a pharmaceutical composition including a hydrophobic therapeutic agent having at least one ionizable functional group and a carrier, wherein the carrier includes an ionizing agent capable of ionizing the ionizable functional group and present in a pre-reaction amount of greater than about 1.5 mole equivalents per mole of ionizable functional group, and a surfactant. In a further aspect of this embodiment, the composition further includes a neutralizing agent capable of neutralizing a portion of the ionizing agent.

In another embodiment, the invention is directed to a pharmaceutical composition including a hydrophobic therapeutic agent having at least one ionizable functional group, and a carrier, wherein the carrier includes an ionizing agent capable of ionizing the ionizable functional group, a surfactant, and a solubilizer present in an amount of greater than about 10% by weight, based on the total weight of the composition. In this embodiment, the surfactant includes at least one compound from the group consisting of alkylglucosides; alkylmaltosides; alkylthioglucosides; lauryl macrogolglycerides; polyoxyethylene alkyl ethers; fatty acids; lower alcohol fatty acid esters; polyoxyethylene alkylphenols; polyethylene glycol fatty acids esters; polypropylene glycol fatty acid esters; glycerol fatty acid esters; acetylated glycerol fatty acid esters; polyethylene glycol glycerol fatty acid esters; polyglyceryl fatty acid esters; polyoxyethylene glycerides; polyoxyethylene sterols, derivatives, and analogues thereof; polyoxyethylene vegetable oils; polyoxyethylene hydrogenated vegetable oils; reaction mixtures of polyols and at least one member of the group consisting of fatty acids, vegetable oils, hydrogenated vegetable oils, and sterols; sugar esters; sugar ethers; sucroglycerides; fatty acid salts; bile salts; phospholipids; phosphoric acid esters; carboxylates; sulfates; and sulfonates.

In another embodiment, the present invention is directed to a pharmaceutical composition including a hydrophobic therapeutic agent having at least one ionizable functional group and a carrier, wherein the carrier includes an ionizing agent capable of ionizing the ionizable functional group, a surfactant, and a solubilizer. In this embodiment, the surfactant includes at least one compound selected from the group consisting of alkylglucosides; alkylmaltosides; alkylthioglucosides; lauryl macrogolglycerides; fatty acids; lower alcohol fatty acid esters; polyoxyethylene alkylphenols; polyethylene glycol fatty acids esters; polypropylene glycol fatty acid esters; glycerol fatty acid esters; acetylated glycerol fatty acid esters; polyethylene glycol glycerol fatty acid esters; polyglyceryl fatty acid esters; polyoxyethylene sorbitan fatty acid esters; polyoxyethylene glycerides; polyoxyethylene sterols, derivatives, and analogues thereof; polyoxyethylene vegetable oils; polyoxyethylene hydrogenated vegetable oils; reaction mixtures of polyols and at least one member of the group consisting of fatty acids, vegetable oils, hydrogenated vegetable oils, and sterols; sugar esters; sugar ethers; sucroglycerides; fatty acid salts; bile salts; phospholipids; phosphoric acid esters; carboxylates; sulfates; and sulfonates.

The solubilizer in this embodiment includes at least one compound selected from the group consisting of alcohols, polyols, amides, esters, and propylene glycol ethers, the alcohol or polyol being selected from the group consisting of ethanol, isopropanol, butanol, benzyl alcohol, ethylene glycol, propylene glycol, butanediols and isomers thereof, glycerol, pentaerythritol, sorbitol, mannitol, dimethyl isosorbide, polypropylene glycol, polyvinylalcohol, hydroxypropyl methylcellulose and other cellulose derivatives, maltodextrins, and cyclodextrins and cyclodextrin derivatives.

In another embodiment, the present invention provides a method of preparing a pharmaceutical composition of an ionizable hydrophobic therapeutic agent. In this embodiment, the method includes the steps of: providing a pharmaceutical composition having an ionizable hydrophobic therapeutic agent and a carrier which includes an ionizing agent and a surfactant; and providing a neutralizing agent to neutralize at least a portion of the ionizing agent.

In another embodiment, the present invention provides a method of treating an animal with an ionizable hydrophobic therapeutic agent. The method includes the steps of providing a pharmaceutical composition having an ionizable hydrophobic therapeutic agent and a carrier which includes an ionizing agent and a surfactant; and administering the pharmaceutical composition to an animal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention overcomes the problems described above characteristic of conventional formulations, by providing pharmaceutical compositions including an ionizable hydrophobic therapeutic agent and a carrier. The carrier includes a surfactant, and an ionizing agent capable of ionizing the ionizable hydrophobic therapeutic agent. Optional components include one or more additional surfactants, solubilizers, triglycerides, neutralizing agents, and various additives. The carrier is able to solubilize the ionizable hydrophobic therapeutic agent and maintain the therapeutic agent in solubilized form for improved delivery to the absorption site The invention also encompasses various dosage forms of the pharmaceutical composition.

The present invention further provides a method of solubilizing ionizable hydrophobic therapeutic agents for improved performance in pharmaceutical compositions. The method includes the steps of providing a pharmaceutical composition as described above, and providing a neutralizing agent to neutralize a portion of the ionizing agent.

Ionizable hydrophobic therapeutic agents suitable for use in the pharmaceutical compositions of the present invention are not particularly limited, as the carrier is surprisingly capable of solubilizing and delivering a wide variety of ionizable hydrophobic therapeutic agents. Ionizable hydrophobic therapeutic agents are compounds with little or no water solubility at neutral pH. Intrinsic water solubilities (i.e., water solubility of the unionized form) for the ionizable hydrophobic therapeutic agents usable in the present invention are less than about 1% by weight, and typically less than about 0.1% or 0.01% by weight. Such therapeutic agents can be any agents having therapeutic or other value when administered to an animal, particularly to a mammal, such as drugs, nutrients, and cosmetics (cosmeceuticals). It should be understood that while the invention is described with particular reference to its value in oral dosage form, the invention is not so limited. Thus, ionizable hydrophobic drugs, nutrients or cosmetics which derive their therapeutic or other value from, for example, topical or transdermal administration, are still considered to be suitable for use in the present invention.

It is a particular feature of the present invention that a wide variety of therapeutic agents can be effectively incorporated in and delivered by the present pharmaceutical compositions. The essential feature of a suitable therapeutic agent is the presence of at least one ionizable functional group. Ionizable functional groups can be acidic groups, or basic groups, with acidic and basic referring to acidic or basic behavior in a Brnsted-Lowry or Lewis acid/base sense. Acidic functional groups are those groups that can be deprotonated by a suitable base to yield the corresponding anionic group (the conjugate base), or groups that can accept an electron pair. Basic functional groups are those groups that can be protonated by a suitable acid to yield the corresponding cationic group (the conjugate acid), or can donate an electron pair. It should be appreciated that the suitability of a therapeutic agent for use in the methods and compositions of the present invention is not determined by its therapeutic class, but is instead determined by the acid-base properties of its acidic or basic functional groups.

The terms acid and base as used herein refer to the ability of a functional group to act as a Brnsted-Lowry acid or Lewis acid, or as a Brnsted-Lowry base or Lewis base, in the presence of an appropriate ionizing agent. For simplicity, the acidic and basic properties of functional groups, ionizing agents, and neutralizing agents are described herein with particular reference to Br nsted-Lowry properties, but the corresponding Lewis acid/base properties are also included within the scope of these terms.

This usage should be contrasted with the terminology typically used in describing whether a compound is acidic or basic based on the pK a of the compound in deionized water. For example, the equivalent pK a of a functional group need not be less than 7 to be considered acidic , since even functional groups with a large pK a can be acidic if they can be deprotonated by a strong base. Similarly, a functional group with an equivalent pK a of less than 7 may still be considered basic if it can be protonated by a stronger acid. Thus, it is the ability of a particular functional group to be ionized (protonated or deprotonated) by a suitable ionizing agent (acid or base) that determines whether a functional group is acidic or basic, rather than the particular pK a associated with that group or with the compound as a whole.

As a specific example, itraconazole is a hydrophobic therapeutic agent having a pK a of 3.7, and a pK b of 10.3. Thus, itraconazole can be protonated by an acid having a pK a less than 3.7, or deprotonated by a base having a pK b less than 10.3.

Suitable therapeutic agents contain at least one ionizable functional group. Of course, many suitable therapeutic agents contain a plurality of such groups, and a single therapeutic agent may contain one or more acidic functional groups as well as one or more basic functional groups. Such therapeutic agents are also within tile scope of the present invention.

In order to avoid particularly cumbersome terminology, the functional groups, whether acidic or basic, are referred to by naming the corresponding free compound. For example, referring to a functional group, the term aminosulfone is used, rather than the more technically precise term aminosulfonyl . This usage is common in the art, and is well understood by one skilled in the art.

Examples of aromatic amines and substituted aromatic amines include, but are not limited to, aniline, N-methylaniline and p-toluidine.

Also included within the scope of the invention are pharmaceutically equivalent derivatives and/or analogs of the ionizable hydrophobic therapeutic agents. Such equivalents include salts, esters, alkyl and acyl derivatives, liposome-encapsulated derivatives, o/w emulsions of derivatives, and the like.

In particular, salts of ionizable hydrophobic therapeutic agents are suitable for use in the present invention. Salts may be used advantageously for the sake of salt exchange with the acid or base ionizing agent, leading to better salt selection.

It should be appreciated that this listing of ionizable hydrophobic therapeutic agents is merely illustrative. Indeed, a particular feature, and surprising advantage, of the compositions of the present invention is the ability of the present compositions to solubilize and deliver a broad range of ionizable hydrophobic therapeutic agents, regardless of therapeutic class. Of course, mixtures of ionizable hydrophobic therapeutic agents may also be used where desired.

The amount of hydrophobic therapeutic agent to be used depends upon the dosage amount to be delivered. One skilled in the art can determine the appropriate dosage amount, depending upon the specific hydrophobic therapeutic agent to be delivered, the nature of the condition treated, the relative efficacy of the therapeutic agent, and other factors commonly considered. The compositions of the present invention can contain a therapeutically effective amount of the therapeutic agent, up to the amount of therapeutic agent that can be solubilized in the carrier. In addition, if desired the compositions can further contain an additional amount of the hydrophobic therapeutic agent suspended (not solubilized) in the carrier.

The ionizing agent can be any pharmaceutically acceptable acid or base capable of protonating or deprotonating the ionizable functional groups of the ionizable hydrophobic therapeutic agent, in a Brnsted-Lowry sense, or capable of accepting or donating an electron pair, in a Lewis sense. For convenience, the ionizing agents are discussed in terms of Brnsted-Lowry properties, although Lewis acids and bases are also suitable ionizing agents.

In one embodiment, the ionizing agent is present in an amount sufficient to ionize at least a portion of the ionizable functional groups. In this embodiment, the ionizing agent preferably is present in an amount of at least about 0.1 mole equivalents per mole of ionizable functional groups. The term mole equivalents as used herein means the number of moles of ionizing functionality effectively presented by the ionizing agent. Thus, for example, when the ionizing agent is a diprotic acid capable of ionizing two moles of basic functional groups per mole of the diprotic acid, only 0.5 moles of the ionizing agent per mole of ionizable functional groups is necessary to provide 1.0 mole equivalents of ionizing agent.

Whether a particular acid is diprotic or polyprotic for purposes of determining the number of mole equivalents for a given concentration depends upon the basicity of the functional group to be ionized. Thus, for example, phosphoric acid is potentially a tri-protic acid, capable of protonating three moles of functional groups per mole of phosphoric acid, in successive ionization steps:

Representing the ionizable basic therapeutic agent as D , the corresponding ionization reaction is:

Each successive ionization step will only occur, however, if the pK a of the acid is less than the pK a of the therapeutic agent. Thus, when the therapeutic agent is, for example, itraconazole, with a pK a of 3.7, only the first reaction will occur to any appreciable extent. With respect to itraconazole, phosphoric acid behaves as a mono-protic acid, and one mole of phosphoric acid provides one mole equivalent of ionizing agent. Similar considerations apply when the ionizing agent is a base, and the ionizable functional group is acidic.

In one embodiment of the invention, the ionizing agent is present in an amount of at least about 0.1 mole equivalents per mole of ionizable functional group. Preferably, the ionizing agent is present in an amount of at least about 0.2 mole equivalents per mole of ionizable functional group, more preferably at least about 0.5 mole equivalents.

When the pharmaceutical composition is intended for formulation in a dosage form that shows poor compatibility with the ionizing agent, such as a gelatin capsule, the ionizing agent is preferably present in an amount of less than about 1.5 mole equivalents per mole of ionizable functional group, and more preferably less than about 1.0 mole equivalents.

In another embodiment of the invention, the ionizing agent is present in an amount of greater than about 1.0 mole equivalents per mole of ionizable functional group. In a further embodiment of the invention, the ionizing agent is present in an amount of greater than about 1.5 mole equivalents per mole of ionizable functional group.

The use of an excess (i.e., greater than 1.0 mole equivalents or greater than 1.5 mole equivalents) of ionizing agent presents several advantages. Since solubilization of the hydrophobic therapeutic agent depends upon the therapeutic agent being ionized, a higher concentration of ionizing agent provides a greater extent of ionization and thus increased i: solubilization. This increased solubilization is particularly important when the acid or base ionization constants (K a or K b ) of the ionizing agent and the therapeutic agent are similar in magnitude. For example, when the ionization constants are within about an order of magnitude of each other, the ionized and un-ionized forms of the therapeutic agent will be in equilibrium, with a significant amount of the therapeutic agent being present in the unionized form. When the ionization constants differ by about two or more orders of magnitude, an equilibrium is still present, but the amount of non-ionized therapeutic agent will be negligibly small.

A further advantage of using an excess of ionizing agent is in ease of preparation. Higher concentrations of ionizing agent facilitate rapid and complete solubilization, making the preparation of solubilized therapeutic agent easier and more efficient, thereby conserving expensive manufacturing and personnel resources.

In addition, it is believed that higher levels of ionizing agent, when used in the compositions of the present invention, advantageously promote continued solubilization of the therapeutic agent, both for storage of the composition, as well as in the gastrointestinal tract upon administration of the composition to a patient.

Although use of higher levels of ionizing agent in the compositions of the present invention presents several advantages, such higher levels are known to be poorly compatible with conventional gelatin capsule dosage forms. Thus, when the dosage form is a gelatin capsule containing the pharmaceutical compositions of the present invention, it is desirable to use a smaller amount of ionizing agent. In a further embodiment of the invention, a composition of the present invention includes an ionizing agent in an amount of greater than about 1.5 mole equivalents per mole of ionizable functional group, and an amount of a neutralizing agent for the ionization agent present in an amount sufficient to at least partially neutralize the excess ionizing agent. For example, if the ionizing agent is an acid, the neutralizing agent would be a base, and vice versa. The pharmaceutically acceptable acids and bases described herein are suitable for use as the neutralizing agent in this embodiment. Thus, this embodiment provides the advantages of increased solubilization and ease of preparation resulting from a high concentration of ionizing agent, while still preserving good compatibility with conventional gelatin capsules by neutralizing some of the excess ionizing agent.

It should be emphasized that when the dosage form is, for example, a liquid drink, neutralization of excess ionizing agent may be unnecessary, and even large excesses of ionizing agent can be used. One skilled in the art can readily determine the amount of excess ionizing agent that can be used, depending upon the ultimate pH of the solution, the degree of bioacceptability of the ionizing agent, the resultant solution taste, and other factors conventional in the art. By way of illustration only, as shown in the Examples herein, the ionizing agent can be used in an amount of several mole equivalents to tens of mole equivalents or more, per mole of ionizable functional group. These large amounts of ionizing agent can also be used when the ultimate dosage form is a gelatin capsule, or when it is desired for any reason to have a lower ionizing agent concentration, by adding a suitable neutralizing agent, as described above.

It should be understood with respect to all of the embodiments described herein that the concentration of ionizing agent given is the concentration prior to the acid-base reaction, unless otherwise noted. Of course, if the concentration of ionizing agent is, for example, 1.0 mole equivalents per mole of ionizable functional group, upon mixing of the ionizing agent and the ionizable pharmaceutical compound, an acid-base reaction will occur, and such reaction will consume some or all of the ionizing agent. Thus, a given concentration of ionizing agent refers to the pre-reaction concentration, and not to the ultimate concentration of the ionizing agent.

The carrier includes at least one surfactant. The surfactant can by hydrophilic, hydrophobic, or a mixture of hydrophilic and hydrophobic surfactants. As is well known in the art, the terms hydrophilic and hydrophobic are relative teyms. To function as a surfactant, a compound must necessarily include polar or charged hydrophilic moieties as well as non-polar hydrophobic (lipophilic) moieties; i.e., a surfactant compound must be amphiphilic. An empirical parameter commonly used to characterize the relative hydrophilicity and hydrophobicity of non-ionic amphiphilic compounds is the hydrophilic-lipophilic balance ( HLB value). Surfactants with lower HLB values are more hydrophobic, and have greater solubility in oils, while surfactants with higher HLB values are more hydrophilic, and have greater solubility in aqueous solutions.

Using HLB values as a rough guide, hydrophilic surfactants are generally considered to be those compounds having an HLB value greater than about 10, as well as anionic, cationic, or zwitterionic compounds for which the HLB scale is not generally applicable. Similarly, hydrophobic surfactants are compounds having an HLB value less than about 10.

It should be appreciated that the HLB value of a surfactant is merely a rough guide generally used to enable formulation of industrial, pharmaceutical and cosmetic emulsions. For many important surfactants, including several polyethoxylated surfactants, it has been reported that HLB values can differ by as much as about 8 HLB units, depending upon the empirical method chosen to determine the HLB value (Schott, J. Pharm. Sciences , 79(1), 87-88 (1990)). Likewise, for certain polypropylene oxide containing block copolymers (poloxamers, available commercially as PLURONIC surfactants, BASF Corp.), the HLB values may not accurately reflect the true physical chemical nature of the compounds. Finally, commercial surfactant products are generally not pure compounds, but are often complex mixtures of compounds, and the HLB value reported for a particular compound may more accurately be characteristic of the commercial product of which the compound is a major component. Different commercial products having the same primary surfactant component can, and typically do, have different HLB values. In addition, a certain amount of lot-to-lot variability is expected even for a single commercial surfactant product. Keeping these inherent difficulties in mind, and using HLB values as a guide, one skilled in the art can readily identify surfactants having suitable hydrophilicity or hydrophobicity for use in the present invention, as described herein.

The compositions of the present invention include at least one surfactant. Suitable surfactants can be ionic hydrophilic surfactants, non-ionic hydrophilic surfactants, or hydrophobic surfactants. The surfactant can be any surfactant suitable for use in pharmaceutical compositions. Suitable hydrophilic surfactants can be anionic, cationic, zwitterionic or non-ionic, although non-ionic hydrophilic surfactants are presently preferred. Preferably, the compositions include at least one non-ionic hydrophilic surfactant. Also preferred are mixtures of two or more non-ionic hydrophilic surfactants, as well as mixtures containing at least one non-ionic hydrophilic surfactant and at least one hydrophobic surfactant.

The choice of specific surfactants should be made keeping in mind the particular hydrophobic therapeutic agent to be used in the composition, and the range of polarity appropriate for the chosen therapeutic agent. With these general principles in mind, a very broad range of surfactants is suitable for use in the present invention. Such surfactants can be grouped into the following general chemical classes detailed in the Tables herein. The HLB values given in the Tables below generally represent the HLB value as reported by the manufacturer of the corresponding commercial product. In cases where more than one commercial product is listed, the HLB value in the Tables is the value as reported for one of the commercial products, a rough average of the reported values, or a value that, in the judgment of the present inventors, is more reliable.

It should be emphasized that the invention is not limited to the surfactants in the Tables, which show representative, but not exclusive, lists of available surfactants.

Although polyethylene glycol (PEG) itself does not function as a surfactant, a variety of PEG-fatty acid esters have useful surfactant properties. Among the PEG-fatty acid monoesters, esters of lauric acid, oleic acid, and stearic acid are most useful. Among the surfactants of Table 1, preferred hydrophilic surfactants include PEG-8 laurate, PEG-8 oleate, PEG-8 stearate, PEG-9 oleate, PEG-10 laurate, PEG-10 oleate, PEG-12 laurate, PEG-12 oleate, PEG-15 oleate, PEG-20 laurate and PEG-20 oleate. Examples of polyethoxylated fatty acid monoester surfactants commercially available are shown in Table 1.

Polyethylene glycol fatty acid diesters are also suitable for use as surfactants in the compositions of the present invention. Representative PEG-fatty acid diesters are shown in Table 2. Among the surfactants in Table 2, preferred hydrophilic surfactants include PEG-20 dilaurate, PEG-20 dioleate, PEG-20 distearate, PEG-32 dilaurate and PEG-32 dioleate.

In general, mixtures of surfactants are also useful in the present invention, including mixtures of two or more commercial surfactant products. Several PEG-fatty acid esters are marketed commercially as mixtures or mono- and diesters. Representative surfactant mixtures are shown in Table 3.

Suitable PEG glycerol fatty acid esters are shown in Table 4. Among the surfactants in the Table, preferred hydrophilic surfactants are PEG-20 glyceryl laurate, PEG-30 glyceryl laurate, PEG-40 glyceryl laurate, PEG-20 glyceryl oleate, and PEG-30 glyceryl oleate.

A large number of surfactants of different degrees of hydrophobicity or hydrophilicity can be prepared by reaction of alcohols or polyalcohols with a variety of natural and/or hydrogenated oils. Most commonly, the oils used are castor oil or hydrogenated castor oil, or an edible vegetable oil such as corn oil, olive oil, peanut oil, palm kernel oil, apricot kernel oil, or almond oil. Preferred alcohols include glycerol, propylene glycol, ethylene glycol, polyethylene glycol, sorbitol, and pentaerythritol. Among these alcohol-oil transesterified surfactants, preferred hydrophilic surfactants are PEG-35 castor oil (Incrocas-35), PEG-40 hydrogenated castor oil (Cremophor RH 40), PEG-25 trioleate (TAGAT TO), PEG-60 corn glycerides (Crovol M70), PEG-60 almond oil (Crovol A70), PEG-40 palm kernel oil (Crovol PK70), PEG-50 castor oil (Emalex C-50), PEG-50 hydrogenated castor oil (Emalex HC-50), PEG-8 caprylic/capric glycerides (Labrasol), and PEG-6 caprylic/capric glycerides (Softigen 767). Preferred hydrophobic surfactants in this class include PEG-5 hydrogenated castor oil, PEG-7 hydrogenated castor oil, PEG-9 hydrogenated castor oil, PEG-6 corn oil (Labrafil M 2125 CS), PEG-6 almond oil (Labrafil M 1966 CS), PEG-6 apricot kernel oil (Labrafil M 1944 CS), PEG-6 olive oil (Labrafil M 1980 CS), PEG-6 peanut oil (Labrafil M 1969 CS), PEG-6 hydrogenated palm kernel oil (Labrafil M 2130 BS), PEG-6 palm kernel oil (Labrafil M 2130 CS), PEG-6 triolein (Labrafil M 2735 CS), PEG-8 corn oil (Labrafil WI, 2609 BS), PEG-20 corn glycerides (Crovol M40), and PEG-20 almond glycerides (Crovol A40). The latter two surfactants are reported to have HLB values of 10, which is generally considered to be the approximate border line between hydrophilic and hydrophobic surfactants. For purposes of the present invention, these two surfactants are considered to be hydrophobic. Representative surfactants of this class suitable for use in the present invention are shown in Table 5.

Esters of propylene glycol and fatty acids are suitable surfactants for use in the present invention. In this surfactant class, preferred hydrophobic surfactants include propylene glycol monolaurate (Lauroglycol FCC), propylene glycol ricinoleate (Propymuls), propylene glycol monooleate (Myverol P-O6), propylene glycol dicaprylate/dicaprate (Captex 200), and propylene glycol dioctanoate (Captex 800). Examples of surfactants of this class are given in Table 7.

In general, mixtures of surfactants are also suitable for use in the present invention. In particular, mixtures of propylene glycol fatty acid esters and glycerol fatty acid esters are suitable and are commercially available. One preferred mixture is composed of the oleic acid esters of propylene glycol and glycerol (Arlacel 186). Examples of these surfactants are shown in Table 8.

A particularly important class of surfactants is the class of mono- and diglycerides. These surfactants are generally hydrophobic. Preferred hydrophobic surfactants in this class of compounds include glyceryl monooleate (Peceol), glyceryl ricinoleate, glyceryl laurate, glyceryl dilaurate (Capmul GDL), glyceryl dioleate (Capmul GDO), glyceryl mono/dioleate (Capmul GMO-K), glyceryl caprylate/caprate (Capmul( MCM), caprylic acid mono/diglycerides (Imwitor 988), and mono- and diacetylated monoglycerides (Myvacet 9-45). Examples of these surfactants are given in Table 9.

Sterols and derivatives of sterols are suitable surfactants for use in the present invention. These surfactants can be hydrophilic or hydrophobic. Preferred derivatives include the polyethylene glycol derivatives. A preferred hydrophobic surfactant in this class is cholesterol. A preferred hydrophilic surfactant in this class is PEG-24 cholesterol ether (Solulan C-24). Examples of surfactants of this class are shown in Table 10.

A variety of PEG-sorbitan fatty acid esters are available and are suitable for use as surfactants in the present invention. In general, these surfactants are hydrophilic, although several hydrophobic surfactants of this class can be used. Among the PEG-sorbitan fatty acid esters, preferred hydrophilic surfactants include PEG-20 sorbitan monolaurate (Tween-20), PEG-20 sorbitan monopalmitate (Tween-40), PEG-20 sorbitan monostearate (Tween-60), and PEG-20 sorbitan monooleate (Tween-80). Examples of these surfactants are shown in Table 11.

Ethers of polyethylene glycol and alkyl alcohols are suitable surfactants for use in the present invention. Preferred hydrophobic ethers include PEG-3 oleyl ether (Volpo 3) and PEG-4 lauryl ether (Brij 30). Examples of these surfactants are shown in Table 12.

Esters of sugars are suitable surfactants for use in the present invention. Preferred hydrophilic surfactants in this class include sucrose monopalmitate and sucrose monolaurate. Examples of such surfactants are shown in Table 13.

Several hydrophilic PEG-alkyl phenol surfactants are available, and are suitable for use in the present invention. Examples of these surfactants are shown in Table 14.

The POE-POP block copolymers are a unique class of polymeric surfactants. The unique structure of the surfactants, with hydrophilic POE and hydrophobic POP moieties in well-defined ratios and positions, provides a wide variety of surfactants suitable for use in the present invention. These surfactants are available under various trade names, including Synperonic PE series (ICI); Pluronic series (BASF), Emkalyx, Lutrol (BASF), Supronic, Monolan, Pluracare, and Plurodac. The generic term for these polymers is poloxamer (CAS 9003-11-6). These polymers have the formula:

where a and b denote the number of polyoxyethylene and polyoxypropylene units, respectively.

Examples of suitable surfactants of this class are shown in Table 15. Since the compounds are widely available, commercial sources are not listed in the Table. The compounds are listed by generic name, with the corresponding a and b values.

Sorbitan esters of fatty acids are suitable surfactants for use in the present invention. Among these esters, preferred hydrophobic surfactants include sorbitan monolaurate (Arlacel 20), sorbitan monopalmitate (Span-40), sorbitan monooleate (Span-80), sorbitan monostearate, and sorbitan tristearate. Examples of these surfactants are shown in Table 16.

Esters of lower alcohols (C 2 to C 4 ) and fatty acids (C 8 to C 18 ) are suitable surfactants for use in the present invention. Among these esters, preferred hydrophobic surfactants include ethyl oleate (Crodamol EO), isopropyl myristate (Crodamol IPM), and isopropyl palmitate (Crodamol IPP). Examples of these surfactants are shown in Table 17.

Ionic surfactants, including cationic, anionic and zwitterionic surfactants, are suitable hydrophilic surfactants for use in the present invention. Preferred anionic surfactants include fatty acid salts and bile salts. Specifically, preferred ionic surfactants include sodium oleate, sodium lauryl sulfate, sodium lauryl sarcosinate, sodium dioctyl sulfosuccinate, sodium cholate, and sodium taurocholate. Examples of such surfactants are shown in Table 18. For simplicity, typical counterions are shown in the entries in the Table. It will be appreciated by one skilled in the art, however, that any bioacceptable counterion may be used. For example, although the fatty acids are shown as sodium salts, other cation counterions can also be used, such as alkali metal cations or ammonium. Unlike typical non-ionic surfactants, these ionic surfactants are generally available as pure compounds, rather than commercial (proprietary) mixtures. Because these compounds are readily available from a variety of commercial suppliers, such as Aldrich, Sigma, and the like, commercial sources are not generally listed in the Table.

TABLE 18 Ionic Surfactants COMPOUND HLB FATTY ACID SALTS >10 Sodium caproate Sodium caprylate Sodium caprate Sodium laurate Sodium myristate Sodium myristolate Sodium palmitate Sodium palmitoleate Sodium oleate 18 Sodium ricinoleate Sodium linoleate Sodium linolenate Sodium stearate Sodium lauryl sulfate (dodecyl) 40 Sodium tetradecyl sulfate Sodium lauryl sarcosinate Sodium dioctyl sulfosuccinate sodium docusate (Cytec) BILE SALTS >10 Sodium cholate Sodium taurocholate Sodium glycocholate Sodium deoxycholate Sodium taurodeoxycholate Sodium glycodeoxycholate Sodium ursodeoxycholate Sodium chenodeoxycholate Sodium taurochenodeoxycholate Sodium glyco cheno deoxycholate Sodium cholylsarcosinate Sodium N-methyl taurocholate PHOSPHOLIPIDS Egg/Soy lecithin Epikuron (Lucas Meyer), Ovothin (Lucas Meyer) Lyso egg/soy lecithin Hydroxylated lecithin Lysophosphatidylcholine Cardiolipin Sphingomyelin Phosphatidylcholine Phosphatidyl ethanolamine Phosphatidic acid Phosphatidyl glycerol Phosphatidyl serine PHOSPHORIC ACID ESTERS Diethanolammonium polyoxyethylene-10 oleyl ether phosphate Esterification products of fatty alcohols or fatty alcohol ethoxylates with phosphoric acid or anhydride CARBOXYLATES Ether carboxylates (by oxidation of terminal OH group of fatty alcohol ethoxylates) Succinylated monoglycerides LAMEGIN ZE (Henkel) Sodium stearyl fumarate Stearoyl propylene glycol hydrogen succinate Mono/diacetylated tartaric acid esters of mono- and diglycerides Citric acid esters of mono-, diglycerides Glyceryl-lacto esters of fatty acids (CFR ref. 172.852) Acyl lactylates: lactylic esters of fatty acids calcium/sodium stearoyl-2-lactylate calcium/sodium stearoyl lactylate Alginate salts Propylene glycol alginate SULFATES AND SULFONATES Ethoxylated alkyl sulfates Alkyl benzene sulfones -olefin sulfonates Acyl isethionates Acyl taurates Alkyl glyceryl ether sulfonates Octyl sulfosuccinate disodium Disodium undecylenamideo-MEA-sulfosuccinate CATIONIC Surfactants >10 Hexadecyl triammonium bromide Decyl trimethyl ammonium bromide Cetyl trimethyl ammonium bromide Dodecyl ammonium chloride Alkyl benzyldimethylammonium salts Diisobutyl phenoxyethoxydimethyl benzylammonium salts Alkylpyridinium salts Betaines (trialkylglycine): Lauryl betaine (N-lauryl,N,N-dimethylglycine) Ethoxylated amines: Polyoxyethylene-15 coconut amine It is surprisingly found that pharmaceutical compositions of ionizable hydrophobic therapeutic agents including at least one surfactant in the carrier are capable of delivering the therapeutic agent without suffering from precipitation of the therapeutic agent in the gastrointestinal tract. In conventional formulations containing an ionizable hydrophobic therapeutic agent and an ionizing agent, the ionizing agent ionizes the therapeutic agent, enabling it to be solubilized. Upon dilution by ambient fluids in the gastrointestinal tract, and exposure to the pH conditions therein, however, such conventional formulations are prone to precipitation of the therapeutic agent. Thus, while the addition of an ionizing agent provides a dosage form of solubilized therapeutic agent, solubilization in vivo remains problematic. In contrast, the formulations of the present invention maintain the therapeutic agent in solubilized form by protecting the therapeutic agent with a surfactant.

Preferably, the carrier includes at least one non-ionic surfactant selected from the group consisting of alkylglucosides; alkylmaltosides; alkylthioglucosides; lauryl macrogolglycerides; polyoxyethylene alkyl ethers; polyoxyethylene alkylphenols; polyethylene glycol fatty acids esters; polyethylene glycol glycerol fatty acid esters; polyoxyethylene sorbitan fatty acid esters; polyoxyethylene-polyoxypropylene block copolymers; polyglyceryl fatty acid esters; polyoxyethylene glycerides; polyoxyethylene sterols, derivatives, and analogues thereof; polyoxyethylene vegetable oils; polyoxyethylene hydrogenated vegetable oils; reaction mixtures of polyols and at least one member of the group consisting of fatty acids, glycerides, vegetable oils, hydrogenated vegetable oils, and sterols; sugar esters, sugar ethers; sucroglycerides; and mixtures thereof.

More preferably, the non-ionic hydrophilic surfactant is selected from the group consisting of polyoxyethylene alkylethers; polyethylene glycol fatty acids esters; polyethylene glycol glycerol fatty acid esters; polyoxyethylene sorbitan fatty acid esters; polyoxyethylene-polyoxypropylene block copolymers; polyglyceryl fatty acid esters; polyoxyethylene glycerides; polyoxyethylene vegetable oils; and polyoxyethylene hydrogenated vegetable oils. The glyceride can be a monoglyceride, diglyceride, triglyceride, or a mixture.

Also preferred are non-ionic hydrophilic surfactants that a-re reaction mixtures of polyols and fatty acids, glycerides, vegetable oils, hydrogenated vegetable oils or sterols. These reaction mixtures are largely composed of the transesterification products of the reaction, along with often complex mixtures of other reaction products. The polyol is preferably glycerol, ethylene glycol, polyethylene glycol, sorbitol, propylene glycol, or pentaerythritol.

In carrier compositions that include at least one hydrophobic surfactant, the hydrophobic surfactant is preferably a surfactant selected from the group consisting of alcohols; polyoxyethylene alkylethers; fatty acids; glycerol fatty acid esters; acetylated glycerol fatty acid esters; lower alcohol fatty acids esters; polyethylene glycol fatty acids esters; polyethylene glycol glycerol fatty acid esters; polypropylene glycol fatty acid esters; polyoxyethylene glycerides; lactic acid derivatives of mono/diglycerides; propylene glycol diglycerides; sorbitan fatty acid esters; polyoxyethylene sorbitan fatty acid esters; polyoxyethylene-polyoxypropylene block copolymers; transesterified vegetable oils; sterols; sterol derivatives; sugar esters; sugar ethers; sucroglycerides; polyoxyethylene vegetable oils; and polyoxyethylene hydrogenated vegetable oils.

As with the hydrophilic surfactants, hydrophobic surfactants can be reaction mixtures of polyols and fatty acids, glycerides, vegetable oils, hydrogenated vegetable oils, and sterols.

Preferably, the hydrophobic surfactant is selected from the group consisting of fatty acids; lower alcohol fatty acid esters; polyethylene glycol glycerol fatty acid esters; polypropylene glycol fatty acid esters; polyoxyethylene glycerides; glycerol fatty acid esters; acetylated glycerol fatty acid esters; lactic acid derivatives of mono/diglycerides; sorbitan fatty acid esters; polyoxyethylene sorbitan fatty acid esters; polyoxyethylene-polyoxypropylene block copolymers; polyoxyethylene vegetable oils; polyoxyethylene hydrogenated vegetable oils; and reaction mixtures of polyols and fatty acids, glycerides, vegetable oils, hydrogenated vegetable oils, and sterols.

Also preferred are mixtures of at least one hydrophilic surfactant and at least one hydrophobic surfactant.

The surfactant or surfactant mixture is present in an amount sufficient to promote the continued solubilization of the therapeutic agent in the gastrointestinal tract. Although small amounts of surfactant may provide some stabilization of the solubilized therapeutic agent, it is presently preferred to include a surfactant in an amount of at least about 10%, preferably about 20-90% by weight, based on the total weight of the composition. Also preferred are mixtures of surfactants, wherein the total amount of surfactant is at least about 10%, and preferably about 20-90% by weight, based on the total weight of the composition.

The carrier optionally includes one or more pharmaceutically acceptable solubilizers to enhance the solubility of the ionizable hydrophobic therapeutic agent in the carrier system. Examples of such compounds include:

ethers of polyethylene glycols having an average molecular weight of about 200 to about 6000, such as tetrahydrofurfuryl alcohol PEG ether (glycofurol, available commercially from BASF under the trade name Tetraglycol) or methoxy PEG (Union Carbide);

Mixtures of solubilizers are also within the scope of the invention. Except as indicated, these compounds are readily available from standard commercial sources.

The amount of solubilizer that can be included in compositions of the present invention is not particularly limited. Of course, when such compositions are ultimately administered to a patient, the amount of a given solubilizer is limited to a bioacceptable amount. In some circumstances, it may be advantageous to include amounts of solubilizers far in excess of bioacceptable amounts in order to maximize the concentration of ionizable hydrophobic therapeutic agent, with excess solubilizer removed prior to providing the composition to a patient using conventional techniques, such as distillation or evaporation.

In a particular embodiment, the solubilizer includes at least one compound selected from the group consisting of alcohols, polyols, amides, esters, and propylene glycol ethers, the alcohol or polyol being selected from the group consisting of ethanol, isopropanol, butanol, benzyl alcohol, ethylene glycol, propylene glycol, butanediols and isomers thereof, glycerol, pentaerythritol, sorbitol, mannitol, dimethyl isosorbide, polypropylene glycol, polyvinylalcohol, hydroxypropyl methylcellulose and other cellulose derivatives, maltodextrins, and cyclodextrins and cyclodextrin derivatives. In this embodiment, the surfactant includes at least one compound selected from the group consisting of alkylglucosides; alkylmaltosides; alkylthioglucosides; lauryl macrogolglycerides; polyoxyethylene alkyl ethers; fatty acids; lower alcohol fatty acid esters; polyoxyethylene alkylphenols; polyethylene glycol fatty acids esters; polypropylene glycol fatty acid esters; glycerol fatty acid esters; acetylated glycerol fatty acid esters; polyethylene glycol glycerol fatty acid esters; polyglyceryl fatty acid esters; polyoxyethylene sorbitan fatty acid esters; polyoxyethylene glycerides; polyoxyethylene sterols, derivatives, and analogues thereof; polyoxyethylene vegetable oils; polyoxyethylene hydrogenated vegetable oils; reaction mixtures of polyols and at least one member of the group consisting of fatty acids, vegetable oils, hydrogenated vegetable oils, and sterols; sugar esters; sugar ethers; sucroglycerides; fatty acid salts; bile salts; phospholipids; phosphoric acid esters; carboxylates; sulfates; and sulfonates.

In another particular embodiment, the solubilizer is present in an amount of greater than about 10% by weight, based on the total weight of the composition. In this embodiment, the surfactant includes at least one compound from the group consisting of alkylglucosides; alkylmaltosides; alkylthioglucosides; lauryl macrogolglycerides; fatty acids; lower alcohol fatty acid esters; polyoxyethylene alkylphenols; polyethylene glycol fatty acid esters; polypropylene glycol fatty acid esters; glycerol fatty acid esters; acetylated glycerol fatty acid esters; polyethylene glycol glycerol fatty acid esters; polyglyceryl fatty acid esters; polyoxyethylene glycerides; polyoxyethylene sterols, derivatives, and analogues thereof; polyoxyethylene vegetable oils; polyoxyethylene hydrogenated vegetable oils; reaction mixtures of polyols and at least one member of the group consisting of fatty acids, vegetable oils, hydrogenated vegetable oils, and sterols; sugar esters, sugar ethers; sucroglycerides; fatty acid salts; bile salts; phospholipids; phosphoric acid esters; carboxylates; sulfates; and sulfonates.

The carrier may also include one or more pharmaceutically acceptable triglycerides to enhance the solubility of the ionizable hydrophobic therapeutic agent in the carrier system. Examples of triglycerides suitable for use in the present invention are shown in Table 19.

6. Other Additives

Other additives conventionally used in pharmaceutical compositions can be included, and these additives are well known in the art. Such additives include antioxidants, preservatives, chelating agents, complexing agents, viscomodulators, tonicifiers, flavorants, colorants odorants, opacifiers, suspending agents, binders, and mixtures thereof. The amounts of such additives can be readily determined by one skilled in the art, according to the particular properties desired.

7. Dosage Forms

The pharmaceutical compositions of the present invention can be provided in the form of a solution preconcentrate; i.e., a composition as described above, and intended to be dispersed with water, either prior to administration, in the form of a drink, or dispersed in vivo. Alternatively, the compositions can be provided in the form of a diluted preconcentrate (i.e., an aqueous dispersion), a semi-solid dispersion or a solid dispersion. If desired, the compositions may be encapsulated in a hard or soft gelatin capsule, a starch capsule or an enteric coated capsule. The term enteric coated capsule as used herein means a capsule coated with a coating resistant to acid; i.e., an acid resistant enteric coating.

Although formulations specifically suited to oral administration are presently preferred, the compositions of the present invention can also be formulated for topical, transdermal, ocular, pulmonary, vaginal, rectal, transmucosal or parenteral administration, in the form of a cream, lotion, ointment, suppository, gel or the like. If such a formulation is desired, other additives may be included, such as are well-known in the art, to impart the desired consistency and other properties to the formulation. The compositions of the present invention can also be formulated as a spray or an aerosol. In particular, the compositions may be formulated as a sprayable solution, and such formulation is particularly useful for spraying to coat a multiparticulate carrier, such as a bead. Such multiparticulate carriers are well known in the art.

8. Preparation of Pharmaceutical Compositions

The pharmaceutical compositions of the present invention can be prepared by conventional methods well known to those skilled in the art. Of course, the specific method of preparation will depend upon the ultimate dosage form. For dosage forms substantially free of water, i.e., when the composition is provided in a pre-concentrated form for later dispersion in an aqueous system, the composition is prepared by simple mixing of the components to form a pre-concentrate. The mixing process can be aided by gentle heating, if desired. For compositions in the form of an aqueous dispersion, the pre-concentrate form is prepared, then the appropriate amount of purified water is added and the solution gently mixed. If any water-soluble additives are included, these may be added first as part of the pre-concentrate, or added later to the aqueous dispersion, as desired. As noted above, the hydrophobic therapeutic agent can be present in a first amount solubilized by the carrier, and a second amount suspended (not solubilized) in the carrier, as desired. It should be emphasized that the order of addition of the various components is not generally important and may be changed as convenient.

In another aspect, the present invention relates to a novel method of preparing a pharmaceutical composition of an ionizable hydrophobic therapeutic agent. The method includes the steps of: (I) providing a pharmaceutical composition having an ionizable hydrophobic therapeutic agent and a carrier which includes an ionizing agent and a surfactant; and (II) providing a neutralizing agent to neutralize at least a portion of the ionizing agent.

The pharmaceutical composition provided in step (I) can be any of the pharmaceutical compositions described herein. Preferably, the composition has greater than about 1.5 mole equivalents of ionizing agent per mole of ionizable functional group, although this concentration is not required.

The neutralizing agent provided in step (II) can be any of the pharmaceutically acceptable acids or bases described above. Of course, if the ionizing agent is an acid, the neutralizing agent is a base, and vice versa. Any amount of neutralizing agent that neutralizes at least a portion of the ionizing agent can be used. Preferably, the amount of neutralizing agent used is an amount sufficient to neutralize the ionizing agent so that the amount of ionizing agent is about 0.1 to about 1.5 mole equivalents per mole of ionizable functional group, based on the amounts of ionizing agent and ionizable functional groups present before reaction with each other, but after reaction of the ionizing agent and the neutralizing agent. More preferably, the neutralizing agent is used in an amount sufficient to neutralize the ionizing agent so that the amount of ionizing agent is about 0.1 to about 1.0 mole equivalents per mole of ionizable functional group.

For some applications, particularly for preparing pharmaceutical compositions in a gelatin capsule dosage form, it may be desirable to use a smaller amount of ionizing agent, in the range of about 0.1 to about 1.5 mole equivalents, preferably about 0.1 to about 1.0 mole equivalents, per mole of ionizable functional group, based on pre-reaction amounts. This lower amount of ionizing agent provides better compatibility with the gelatin capsule dosage form. However, as discussed above, it is desirable to use an excess of ionizing agent to promote increased solubilization and ease of preparation of solubilized compositions. Thus, in the present method, an excess of ionizing agent can be used in preparing a composition, and a portion of the excess can then be neutralized to provide a composition more suited to certain dosage forms, particularly gelatin capsule dosage forms.

The amount of neutralizing agent used is defined in such a way as to make the relative amounts of ionizing agent and ionizable functional groups in the present method consistent with the description above. Thus, it is convenient to define the amount of ionizing agent as the pre-reaction amount, before the acid-base reaction with the ionizable functional groups, as described above. In order to keep this convention, the amount of neutralizing agent is defined by adopting the following convenient fiction: first, the neutralizing agent is imagined to react with the ionizing agent, to neutralize a portion of the ionizing agent; then, the remaining ionizing agent is imagined to react with the ionizable functional groups, to ionize at least a portion of the ionizable functional groups. Thus, in a preferred embodiment, the amount of neutralizing agent is selected so that after the first step of the hypothetical two-step ionization i.e., the neutralization reaction between the neutralizing agent and the ionizing agent the amount of ionizing agent available in the second step is about 0.1 to about 1.5 mole equivalents, preferably about 0.1 to about 1.0 mole equivalents, per mole of ionizable functional group.

As a specific example, if the amount of ionizable functional groups is 1.0 mole, and the amount of ionizing agent used is 10.0 moles, then to achieve a concentration of ionizing agent within a pre-reaction range of 0.1 to 1.5 moles, an amount of neutralizing agent sufficient to neutralize from 8.5 to 9.9 moles of ionizing agent is used. In the hypothetical first neutralization step, the 8.5 to 9.9 mole equivalents of neutralizing agent neutralizes 8.5 to 9.9 moles of the ionization agent, leaving 0.1 to 1.5 moles unreacted. Thus, the amount of ionizing agent hypothetically present before reaction with the ionizable functional group is 0.1 to 1.5 moles. It should be apparent that the actual reaction sequence does not follow this hypothetical scheme, but such a scheme merely provides a simple stoichiometric reference frame.

9. Methods of Treating an Animal

In another aspect, the present invention relates to methods of improving delivery of ionizable hydrophobic therapeutic agents in an animal by administering to the animal a dosage form of the pharmaceutical compositions described herein. Preferably the animal is a mammal, and more preferably, a human. It is believed that the pharmaceutical compositions of the present invention when administered to an animal enable the ionizable hydrophobic therapeutic agent contained therein to be delivered to the absorption site with less or no precipitation of the therapeutic agent, resulting in better bioavailability.

In use, the methods and compositions of the present invention provide a number of important advantages, including:

Robustness to Dilution: The compositions of the present invention are unexpectedly robust to dilution in media simulating the conditions normally encountered in the gastrointestinal and intestinal tracts. Precipitation of the therapeutic agent is minimal, and is delayed upon administration, due to the protective effects of the surfactant and optional solubilizer components.

Improved Delivery: The compositions of the present invention unexpectedly provide improved delivery of the therapeutic agent to the absorption site, by minimizing precipitation. This improved delivery is believed to result in better bioavailability of the therapeutic agent.

Less Dependence Upon Other Factors: The compositions of the present invention enable the absorption of the hydrophobic therapeutic agent independent of wetting/dissolution rates, and less dependent upon meal, gastro-intestinal contents, and bilary secretions, by maintaining the therapeutic agent in solubilized form upon administration. In addition, when the optional triglyceride component is absent, dependence upon the rate of lipolysis is reduced or eliminated.

High Loading Capacity: The compositions of the present invention provide high loading capacity for ionizable hydrophobic therapeutic agents. The surfactants and optional triglycerides and solubilizers interact with the hydrophobic therapeutic agent to unexpectedly solubilize large amounts of therapeutic agent. In addition, when an additional non-solubilized amount of therapeutic agent is included, still larger therapeutic agent concentrations can be achieved, while still preserving the advantages in stability and bioavailability of the solubilized therapeutic agent.

Ease of Preparation: The methods of the present invention provide compositions in which the hydrophobic therapeutic agent is readily solubilized, thereby conserving expensive manufacturing and personnel resources.

Versatility: Because the compositions of the present invention can effectively make use of a wide variety of different surfactants, solubilizers and triglycerides to solubilize a wide variety of ionizable hydrophobic therapeutic agents, compositions can be carefully tailored to the polarity and functionality of the therapeutic agents, without compromising the improved solubilization, delivery, and other advantages as described above.

These and other advantages of the present invention, as well as aspects of preferred embodiments, are illustrated more fully in the Examples which follow.

EXAMPLES

Carrier Formulations

Carrier formulations can be prepared by simple mixing of the desired components, with gentle heating if desired. Table 20 contains examples of carrier formulations according to the present invention, using a wide variety of surfactants, surfactant mixtures, solubilizers, and other components. The desired amount of ionizable hydrophobic therapeutic agent is included in the carrier to produce a pharmaceutical composition.

Stability of Solutions of Itraconazole upon Dilution in Simulated Gastric Fluid

Carriers were prepared according to Example 1, using the specific carrier formulations shown in Example 1 as Nos. 27-31. From 10 to 85 mg of itraconazole was included in the carriers, as indicated in Table 21. An aliquot of each solution of itraconazole was diluted 100-fold in an enzyme-free simulated gastric fluid (SGF). The diluent was incubated at 37 C. while being tumbled on a rotor. At the indicated time during the incubation, the amount of itraconazole remaining solubilized in the diluent was determined by drug specific HPLC, as a measure of the stability of these formulations in the SGF. A dosage form of a commercial oral itraconazole product, SPORANOX (a 10 mg/mL drink solution) was also tested under the same experimental conditions, for comparison.

Stability of Solutions of Itraconazole upon Dilution in Simulated Intestinal Fluid

Carriers were prepared according to Example 1, using the specific carrier formulations shown in Example 1 as Nos. 27-29 and 3 1. From 10 to 85 mg of itraconazole was included in the carriers, as indicated in Table 22. An aliquot of each solution of itraconazole was diluted 100-fold in an enzyme-free simulated intestinal fluid (SIF). The diluent was incubated at 37 C. while being tumbled on a rotor. At the indicated time during the incubation, the amount of itraconazole remaining solubilized in the diluent was determined by HPLC, as a measure of the stability of these formulations in the SIF. Two dosage forms of a commercial oral itraconazole product, SPORANOX (a 10 mg/mL drink solution and a 100 mg hard gelatin capsule) were also tested under the same experimental conditions, for comparison.

Stability of Solutions of Tretinoin upon Dilution in Simulated Gastric Fluid

Example 2 was repeated, but using tretinoin as the ionizable hydrophobic therapeutic agent and formulation Nos. 65 and 66 as the carrier. The results are shown in Table 23.

Stability of Solutions of Tretinoin upon Dilution in Simulated Intestinal Fluid

Example 4 was repeated in simulated intestinal fluid instead of simulated gastric fluid. The results are shown in Table 24.

TABLE 24 Stability of Compositions in SIF % Tretinoin Remaining Solubilized Formulation Tretinoin (mg/mL) in the Diluent After 3 hr. 65 10 92.5 66 10 53.7 The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.