Title:  Polymeric delivery formulations of leuprolide with improved efficacy

United States Patent:  6,565,874

Issued:  May 20, 2003

Inventors:  Dunn; Richard L. (Fort Collins, CO); Garrett; John Steven (Fort Collins, CO); Ravivarapu; Harish (Union City, CA); Chandrashekar; Bhagya L (Fort Collins, CO)

Assignee:  Atrix Laboratories (Fort Collins, CO)

Appl. No.:  711758

Filed:  November 13, 2000

The present invention is directed to a flowable composition that is suitable for use as a controlled release implant. The flowable composition includes a biodegradable thermoplastic polyester that is at least substantially insoluble in aqueous medium or body fluid. The flowable composition also includes a biocompatible polar aprotic solvent. The biocompatible polar aprotic solvent is miscible to dispersible in aqueous medium or body fluid. The flowable composition also includes leuprolide acetate.

DETAILED DESCRIPTION OF THE INVENTION

Specific and preferred biodegradable thermoplastic polyesters and polar aprotic solvents; ranges of thermoplastic polyesters, polar aprotic solvents, leuprolide acetate, and flowable compositions; molecular weights of the thermoplastic polyester; and ranges of the solid implant described herein below are for illustration only; they do not exclude other biodegradable thermoplastic polyesters and polar aprotic solvents; ranges of thermoplastic polyesters, polar aprotic solvents, leuprolide acetate, and flowable compositions; molecular weights of the thermoplastic polyester; and ranges of the solid implant.

The present invention provides a flowable composition suitable for use as a controlled release implant, a method for forming the flowable composition, a method for using the flowable composition, the biodegradable implant that is formed in situ from the flowable composition, a method of forming the biodegradable implant in situ, a method for using the biodegradable implant that is formed in situ, a kit that includes the flowable composition, and the solid implant. The flowable composition may be used to provide a biodegradable or bioerodible microporous in situ formed implant in animals. The flowable composition is composed of a biodegradable thermoplastic polymer or copolymer in combination with a suitable polar aprotic solvent. The biodegradable thermoplastic polyesters or copolymers are substantially insoluble in water and body fluid, biocompatible, and biodegradable and/or bioerodible within the body of an animal. The flowable composition is administered as a liquid or gel to tissue wherein the implant is formed in situ. The composition is biocompatible and the polymer matrix does not cause substantial tissue irritation or necrosis at the implant site. The implant can be used to deliver leuprolide acetate.

Preferably, the flowable composition can be a liquid or a gel, suitable for injection in a patient (e.g., human). As used herein, "flowable" refers to the ability of the composition to be injected through a medium (e.g., syringe) into the body of a patient. For example, the composition can be injected, with the use of a syringe, beneath the skin of a patient. The ability of the composition to be injected into a patient will typically depend upon the viscosity of the composition. The composition will therefore have a suitable viscosity, such that the composition can be forced through the medium (e.g., syringe) into the body of a patient. As used herein, a "liquid" is a substance that undergoes continuous deformation under a shearing stress. Concise Chemical and Technical Dictionary, 4th Enlarged Ed., Chemical Publishing Co., Inc., p. 707, NY, N.Y. (1986). As used herein, a "gel" is a substance having a gelatinous, jelly-like, or colloidal properties. Concise Chemical and Technical Dictionary, 4th Enlarged Ed., Chemical Publishing Co., Inc., p. 567, NY, N.Y. (1986).

Biodegradable Thermoplastic Polyester

A thermoplastic composition is provided in which a solid, biodegradable polyester and leuprolide acetate are dissolved in a biocompatible polar aprotic solvent to form a flowable composition, which can then be administered via a syringe and needle. Any suitable biodegradable thermoplastic polyester can be employed, provided the biodegradable thermoplastic polyester is at least substantially insoluble in aqueous medium or body fluid. Suitable biodegradable thermoplastic ;polyesters are disclosed, e.g., in U.S. Patent Nos. 5,324,519; 4,938,763; 5,702,716; 5,744,153; and 5,990,194; wherein the suitable biodegradable thermoplastic polyester is disclosed as a thermoplastic polymer. Examples of suitable biodegradable thermoplastic polyesters include polylactides, polyglycolides, polycaprolactones, copolymers thereof, terpolymers thereof, and any combinations thereof. Preferably, the suitable biodegradable thermoplastic polyester is a polylactide, a polyglycolide, a copolymer thereof, a terpolymer thereof, or a combination thereof.

The type, molecular weight, and amount of biodegradable thermoplastic polyester present in the composition will typically depend upon the desired properties of the controlled release implant. For example, the type, molecular weight, and amount of biodegradable thermoplastic polyester can influence the length of time in which the leuprolide acetate is released from the controlled release implant. Specifically, in one embodiment of the present invention, the composition can be used to formulate a one month delivery system of leuprolide acetate. In such an embodiment, the biodegradable thermoplastic polyester can preferably be 50/50 poly (DL-lactide-co-glycolide) having a carboxy terminal group; can be present in about 30 wt. % to about 40 wt. % of the composition; and can have an average molecular weight of about 23,000 to about 45,000. Alternatively, in another embodiment of the present invention, the composition can be used to formulate a three month delivery system of leuprolide acetate. In such an embodiment, the biodegradable thermoplastic polyester can preferably be 75/25 poly (DL-lactide-co-glycolide) without a carboxy terminal group; can be present in about 40 wt. % to about 50 wt. % of the composition; and can have an average molecular weight of about 15,000 to about 24,000.

The terminal groups of the poly(DL-lactide-co-glycolide) can either be hydroxyl, carboxyl, or ester depending upon the method of polymerization. Polycondensation of lactic or glycolic acid will provide a polymer with terminal hydroxyl and carboxyl groups. Ring-opening polymerization of the cyclic lactide or glycolide monomers with water, lactic acid, or glycolic acid will provide polymers with the same terminal groups. However, ring-opening of the cyclic monomers with a monofunctional alcohol such as methanol, ethanol, or 1-dodecanol will provide a polymer with one hydroxyl group and one ester terminal groups. Ring-opening polymerization of the cyclic monomers with a diol such as 1,6-hexanediol or polyethylene glycol will provide a polymer with only hydroxyl terminal groups.

Thermoplastic Polyester Molecular Weight

The molecular weight of the polymer used in the present invention can affect the rate of leuprolide acetate release as long as the flowable composition has been used as an intermediate. Under these conditions, as the molecular weight of the polymer increases, the rate of leuprolide acetate release from the system decreases. This phenomenon can be advantageously used in the formulation of systems for the controlled release of leuprolide acetate. For relatively quick release of leuprolide acetate, low molecular weight polymers can be chosen to provide the desired release rate. For release of a leuprolide acetate over a relatively long period of time, a higher polymer molecular weight can be chosen. Accordingly, a polymer system can be produced with an optimum polymer molecular weight range for the release of leuprolide acetate over a selected length of time.

The molecular weight of a polymer can be varied by any of a variety of methods. The choice of method is typically determined by the type of polymer composition. For example, if a thermoplastic polyester is used that is biodegradable by hydrolysis, the molecular weight can be varied by controlled hydrolysis, such as in a steam autoclave. Typically, the degree of polymerization can be controlled, for example, by varying the number and type of reactive groups and the reaction times.

Polar Aprotic Solvent

Any suitable polar aprotic solvent can be employed, provided the suitable polar aprotic solvent is miscible to dispersible in aqueous medium or body fluid. Suitable polar aprotic solvents are disclosed, e.g., in Aldrich Handbook of Fine Chemicals and Laboratory Equipment, Milwaukee, Wis. (2000); U.S. Pat. Nos. 5,324,519; 4,938,763; 5,702,716; 5,744,153; and 5,990,194. The suitable polar aprotic solvent should be able to diffuse into body fluid so that the flowable composition coagulates or solidifies. It is also preferred that the polar aprotic solvent for the biodegradable polymer be non-toxic and otherwise biocompatible. The polar aprotic solvent is preferably biocompatible. Examples of suitable polar aprotic solvents include polar aprotic solvents having an amide group, an ester group, a carbonate group, a ketone, an ether, a sulfonyl group, or a combination thereof. Preferably, the polar aprotic solvent can be N-methyl-2-pyrrolidone, 2-pyrrolidone, N, N-dimethylformamide, dimethyl sulfoxide, propylene carbonate, caprolactam, triacetin, or any combination thereof. More preferably, the polar aprotic solvent can be N-methyl-2-pyrrolidone.

The polar aprotic solvent can be present in any suitable amount, provided the polar aprotic solvent is miscible to dispersible in aqueous medium or body fluid. The type and amount of biocompatible polar aprotic solvent present in the composition will typically depend upon the desired properties of the controlled release implant. For example, the type and amount of biocompatible polar aprotic solvent can influence the length of time in which the leuprolide acetate is released from the controlled release implant. Specifically, in one embodiment of the present invention, the composition can be used to formulate a one month delivery system of leuprolide acetate. In such an embodiment, the biocompatible polar aprotic solvent can preferably be N-methyl-2-pyrrolidone and can preferably present in about 60 wt. % to about 70 wt. % of the composition. Alternatively, in another embodiment of the present invention, the composition can be used to formulate a three month delivery system of leuprolide acetate. In such an embodiment, the biocompatible polar aprotic solvent can preferably be N-methyl-2-pyrrolidone and can preferably present in about 50 wt. % to about 60 wt. % of the composition.

The solubility of the biodegradable thermoplastic polyesters in the various polar aprotic solvents will differ depending upon their crystallinity, their hydrophilicity, hydrogen-bonding, and molecular weight. Thus, not all of the biodegradable thermoplastic polyesters will be soluble in the same polar aprotic solvent, but each biodegradable thermoplastic polymer or copolymer should have its appropriate polar aprotic solvent. Lower molecular-weight polymers will normally dissolve more readily in the solvents than high-molecular-weight polymers. As a result, the concentration of a polymer dissolved in the various solvent will differ depending upon type of polymer and its molecular weight. Conversely, the higher molecular-weight polymers will normally tend to coagulate or solidify faster than the very low-molecular-weight polymers. Moreover the higher molecular-weight polymers will tend to give higher solution viscosities than the low-molecular-weight materials.

For example, low-molecular-weight polylactic acid formed by the condensation of lactic acid will dissolve in N-methyl-2-pyrrolidone(NMP) to give a 73% by weight solution which still flows easily through a 23-gauge syringe needle, whereas a higher molecular-weight poly(DL-lactide) (DL-PLA) formed by the additional polymerization of DL-lactide gives the same solution viscosity when dissolved in NMP at only 50% by weight. The higher molecular-weight polymer solution coagulates immediately when placed into water. The low-molecular-weight polymer solution, although more concentrated, tends to coagulate very slowly when placed into water.

It has also been found that solutions containing very high concentrations of high-molecular-weight polymers sometimes coagulate or solidify slower than more dilute solutions. It is suspected that the high concentration of polymer impedes the diffusion of solvent from within the polymer matrix and consequently prevents the permeation of water into the matrix where it can precipitate the polymer chains. Thus, there is an optimum concentration at which the solvent can diffuse out of the polymer solution and water penetrates within to coagulate the polymer.

The leuprolide acetate is preferably lyophilized prior to use. Typically, the leuprolide acetate can be dissolved in an aqueous solution, sterile filtered, and lyophilized in a syringe. The polymer/solvent solution can be filled into another syringe. The two syringes can then be coupled together and the contents can be drawn back and forth between the two syringes until the polymer/solvent solution and the leuprolide acetate are effectively mixed together, forming a flowable composition. The flowable composition can be drawn into one syringe. The two syringes can then be disconnected. A needle can be inserted onto the syringe containing the flowable composition. The flowable composition can then be injected through the needle into the body. The flowable composition can be formulated and administered to a patient as described in, e.g., U.S. Pat. Nos. 5,324,519; 4,938,763; 5,702,716; 5,744,153; and 5,990,194; or as described herein. Once in place, the solvent dissipates, the remaining polymer solidifies, and a solid structure is formed. The solvent will dissipate and the polymer will solidify and entrap or encase the leuprolide acetate within the solid matrix.

The release of leuprolide acetate from these solid implants will follow the same general rules for release of a drug from a monolithic polymeric device. The release of leuprolide acetate can be affected by the size and shape of the implant, the loading of leuprolide acetate within the implant, the permeability factors involving the leuprolide acetate and the particular polymer, and the degradation of the polymer. Depending upon the amount of leuprolide acetate selected for delivery, the above parameters can be adjusted by one skilled in the art of drug delivery to give the desired rate and duration of release.

The amount of leuprolide acetate incorporated into the flowable, in-situ, solid forming implant depends upon the desired release profile, the concentration of leuprolide acetate required for a biological effect, and the length of time that the leuprolide acetate has to be released for treatment. There is no critical upper limit on the amount of leuprolide acetate incorporated into the polymer solution except for that of an acceptable solution or dispersion viscosity for injection through a syringe needle. The lower limit of leuprolide acetate incorporated into the delivery system is dependent simply upon the activity of the leuprolide acetate and the length of time needed for treatment. Specifically, in one embodiment of the present invention, the composition can be used to formulate a one month delivery system of leuprolide acetate. In such an embodiment, the leuprolide acetate can preferably be present in about 2 wt. % to about 4 wt. % of the composition. Alternatively, in another embodiment of the present invention, the composition can be used to formulate a three month delivery system of leuprolide acetate. In such an embodiment, the leuprolide acetate can preferably be present in about 4 wt. % to about 8 wt. % of the composition. The solid implant formed from the flowable system will release the leuprolide acetate contained within its matrix at a controlled rate until the leuprolide acetate is effectively depleted.

Dosages

The amount of flowable composition administered will typically depend upon the desired properties of the controlled release implant. For example, the amount of flowable composition can influence the length of time in which the leuprolide acetate is released from the controlled release implant. Specifically, in one embodiment of the present invention, the composition can be used to formulate a one month delivery system of leuprolide acetate. In such an embodiment, about 0.20 mL to about 0.40 mL of the flowable composition can be administered. Alternatively, in another embodiment of the present invention, the composition can be used to formulate a three month delivery system of leuprolide acetate. In such an embodiment, about 0.30 mL to about 0.50 mL of the flowable composition can be administered.

Surprisingly, it has been discovered that the liquid polymeric compositions according to the present invention are more effective in delivering leuprolide acetate than Lupron.RTM. Depot. Specifically, as shown in the Examples below, the testosterone levels obtained with the liquid polymeric compositions of the present invention containing the leuprolide acetate are lower at extended times in dogs compared to Lupron.RTM. Depot, and also at the six month point in humans, compared to the value reported in the literature for Lupron.RTM. Depot (Sharifi, R., J. Urology, Vol. 143, Jan., 68 (1990)).

Claim 1 of 49 Claims

What is claimed is:

1. A flowable composition suitable for use as a controlled release implant, the composition comprising:

(a) a biodegradable thermoplastic polyester that is at least substantially insoluble in aqueous medium or body fluid;

(b) a biocompatible polar aprotic solvent selected from the group consisting of an amide, an ester, a carbonate, a ketone, an ether, and a sulfonyl; wherein the biocompatible polar aprotic solvent is miscible to dispersible in aqueous medium or body fluid; and

(c) uncomplexed leuprolide acetate that is the only source of leuprolide in the composition.
 

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