HK1053783B - Use of ritonavir (abt-538) for improving the pharmacokinetics of drugs metabolized by cytochrome p450 in a method of treating aids - Google Patents

Description

Technical Field

The present invention relates to a novel composition and a method for improving the pharmacokinetics of drugs which are metabolized by cytochrome P450 monooxygenase.

Background of the Invention

It has recently been disclosed that the HIV protease inhibitor ritonavir (also known as ABT-538) is effective in humans for inhibiting an HIV infection.

It has also been discovered that ritonavir is an inhibitor of the metabolic enzyme cytochrome P450 monooxygenase.

Some drugs are metabolized by cytochrome P450 monooxygenase, leading to unfavorable pharmacokinetics and the need for more frequent and higher doses than are most desirable. Administration of such drugs with an agent that inhibits metabolism by cytochrome P450 monooxygenase will improve the pharmacokinetics (i.e., increase half-life, increase the time to peak plasma concentration, increase blood levels) of the drug.

It has been discovered that coadministration of ritonavir with a drug which is metabolized by cytochrome P450 monooxygenase, especially the P450 3A4 isozyme, causes an improvement in the pharmacokinetics of such a drugs.

Disclosure of the Invention

In accordance with the present invention, there is disclosed a method of improving the pharmacokinetics of a drug (or a pharmaceutically acceptable salt thereof) which is metabolized by cytochrome P450 monooxygenase comprising coadministering ritonavir or a pharmaceutically acceptable salt thereof. When administered in combination, the two therapeutic agents can be formulated as separate compositions which are administered at the same time or different times, or the two therapeutic agents can be administered as a single composition.

Drugs which are metabolized by cytochrome P450 monooxygenase and which benefit from coadministration with ritonavir include the immunosuppressants cyclosporine, FK-506 and rapamycin, the chemotherapeutic agents taxol and taxotere and the antibiotic clarithromycin

More specifically the invention concerns:

1. 1. A combination of ritonavir or a pharmaceutically acceptable salt thereof and a drug which is metabolized by cytochrome P450 monooxygenase 3A4, to improve the pharmacokinetics of the drug, provided that the drug is other than an HIV protease inhibitor.
2. 2. A combination according to 1, where ritonavir and the drug are formulated as a single composition.
3. 3. A combination according to 1, where ritonavir and the drug are formulated as separate compositions.
4. 4. A combination according to any one of 1-3, wherein the dose of ritonavir is from 0.001 to 300mg/kg body weight of the human to which it is to be administered.
5. 5. A combination according to any one of 1-4, wherein the drug is cyclosporine, FK-506, rapamycin, taxol, taxotere or clarithromycin.

Ritonavir is (2S,3S,5S)-5-(N-(N-((N-Methyl-N-((2-isopropyl-4-thiazolyl)methyl)amino)carbonyl)-L-valinyl)amino)-2-(N-((5-thiazolyl)methoxycarbonyl)amino)-1,6-diphenyl-3-hydroxyhexane or a pharmaceutically acceptable salt thereof. Ritonavir can be synthesized by the procedures disclosed in PCT Patent Application No. WO94/14436, published July 7, 1994 , and the U.S. patent application Serial No. 08/469,965, filed June 6, 1995 .

Inhibition of Cytochrome P450

The ability of ritonavir to inhibit cytochrome P450 monooxygenase activity was tested with terfenadine as the probe substrate (Yun, et al., Drug Metabolism & Disposition, Vol. 21 403-407 (1993)). Ritonavir inhibited the terfenadine hydroxylase activity representing the most abundant form of cytochrome P450 (CYP3A4) present in human liver with an IC₅₀ of 0.25 µM.

Pharmacokinetic Improvement

The ability of ritonavir to improve the pharmacokinetics of a compound which is metabolized by cytochrome P450 monooxygenase can be demonstrated by the test method described below, wherein VX-478 is used as an example (not part or the invention).

Rats (male, Sprague-Dawley derived, 0.3-0.45 kg) were fasted overnight prior to dosing, but were permitted water ad libitum. For combination dosing, a single solution containing both ritonavir and VX-478 (5 mg/ml each) was prepared in a vehicle of 20% ethanol : 30% propylene glycol and D5W with an appropriate number of molar equivalents of methane sulfonic acid to assist in solubilization. Separate solutions of VX-478 and ritonavir were also prepared and these solutions were used to evaluate the pharmacokinetics of VX-478 and ritonavir when administered as a single agent in rats. The solutions, administered orally by gavage to a group of rats at a dose volume of 2 ml/kg, provided a 10 mg/kg dose of each compound. Blood samples were obtained from a tail vein of each rat 0.25, 0.5, 1, 1.5, 2, 3, 4, 6 and 8 hours after dosing. The plasma was separated from the red cells by centrifugation and frozen (-30°C) until analysis. Concentrations of both ritonavir and VX-478 were determined simultaneously by reverse phase HPLC with low wavelength UV detection following liquid-liquid extraction of the plasma samples. The peak plasma concentration (C_max) and time to peak plasma concentration (T_max) for each rat were obtained directly from the plasma concentration data. The area under the curve was calculated by the trapezoidal method over the time course of the study. The plasma elimination half life was obtained from NONLIN84 or from a log-linear regression of the terminal plasma concentrations as a function of time after dosing. Each combination was evaluated in a group containing at least three rats; the values reported are averages for each group of animals. The data obtained from the combination was compared to data obtained from a separate group of rats which received a single, separate dose of the compound under evaluation.

Below in Table 1 are shown the results from the pharmacokinetic experiments with VX-478 and other HIV protease inhibitors not part of the invention in rats. The maximum plasma levels (C_max), time to maximum plasma level (T_max) and area under the plasma concentration curve (AUC) for an 8-hour sampling interval following dosing of the HIV protease inhibitor alone vs. dosing in combination with ritonavir are provided.

Compound	Cmax (mcg/ml)	Tmax (hr)	AUC(0-8h) (mcg•hr/ml)
VX-478‡	1.61	0.42	1.69
VX-478 (+ritonavir)	2.88	1.5	13.50
A-77003‡	0.07	0.25	0.025
A-77003 (+ritonavir)	0.96	0.67	1.39
A-80987‡	2.42	0.25	1.45
A-80987 (+ritonavir)	4.47	1.7	25.74
Saquinavir‡	0.08	0.18	0.029
Saquinavir (+ritonavir)	1.48	3.0	8.52
MK-639‡	1.03	0.5	0.81
MK-639 (+ritonavir)	1.40	3.0	6.51
AG1343‡	0.40	0.75	1.14
AG1343 (+ritonavir)	1.81	4.0	11.92

‡ compound administered as a single agent

The ability of ritonavir to improve the pharmacokinetics of clarithromycin in humans was demonstrated according to the method described below.

Clarithromycin (500 mg/BIAXIN^® tablet every 12 hours) and a combination of ritonavir (200 mg of liquid formulation every 8 hours) and clarithromycin (500 mg every 12 hours) were administered to groups of 4 healthy human volunteers. Blood samples were collected on day four of dosing for HPLC determination of plasma concentrations of clarithromycin.

Below in Table 2 are shown the results from the pharmacokinetic experiments with ciarithromycin in humans. The mean maximum plasma levels (C_max) and area under the plasma concentration curve (AUC) calculated using noncompartmental methods for the 0-24 hour time interval on day four of dosing of clarithromycin alone vs. dosing in combination with ritonavir are provided.

Compound	Cmax (mcg/ml)	AUC(0-24h) (mcg•hr/ml)
clarithromycin‡	3.93	49.04
clarithromycin (+ritonavir)	5.13	86.88

‡ compound administered as a single agent

The therapeutic agents of the present invention can be used in the form of salts derived from inorganic or organic acids. These salts include but are not limited to the following: acetate, adipate, alginate, citrate, aspartate, benzoate, benzenesulfonate, bisulfate, butyrate, camphorate, camphorsulfonate, digluconate, cyclopentanepropionate, dodecylsulfate, ethanesulfonate, glucoheptanoate, glycerophosphate, hemisulfate, heptanoate, hexanoate, fumarate, hydrochloride, hydrobromide, hydroiodide, 2-hydroxyethanesulfonate (isethionate), lactate, maleate, methanesulfonate, nicotinate, 2-naphthalenesulfonate, oxalate, pamoate, pectinate, persulfate, 3-phenylpropionate, picrate, pivalate, propionate, succinate, tartrate, thiocyanate, p-toluenesulfonate and undecanoate. Also, the basic nitrogen-containing groups can be quaternized with such agents as loweralkyl halides, such as methyl, ethyl, propyl, and butyl chloride, bromides, and iodides; dialkyl sulfates like dimethyl, diethyl, dibutyl, and diamyl sulfates, long chain halides such as decyl, lauryl, myristyl and stearyl chlorides, bromides and iodides, aralkyl halides like benzyl and phenethyl bromides, and others. Water or oil-soluble or dispersible products are thereby obtained.

Examples of acids which may be employed to form pharmaceutically acceptable acid addition salts include such inorganic acids as hydrochloric acid, sulphuric acid and phosphoric acid and such organic acids as oxalic acid, maleic acid, succinic acid and citric acid. Other salts include salts with alkali metals or alkaline earth metals, such as sodium, potassium, calcium or magnesium or with organic bases.

The administration of ritonavir and a compound which is metabolized by cytochrome P450 monooxygenase is useful for improving in humans the pharmacokinetics of the compound which is metabolized by cytochrome P450 monooxygenase.

The total daily dose of ritonavir to be administered to a human or other mammal host in single or divided doses may be in amounts, for example, from 0.001 to 300 mg/kg body weight daily and more usually 0.1 to 50 mg/kg and even more usually 0.1 to 25 mg/kg. Dosage unit compositions may contain such amounts of submultiples thereof to make up the daily dose.

The total daily dose of the drug which is metabolized by cytochrome P450 monooxygenase to be administered to a human or other mammal is well known and can be readily determined by one of ordinary skill in the art. Dosage unit compositions may contain such amounts of submultiples thereof to make up the daily dose.

The amount of active ingredient that may be combined with the carrier materials to produce a single dosage form of each drug, individually or in combination, will vary depending upon the host treated and the particular mode of administration.

It will be understood, however, that the specific dose level for any particular patient will depend upon a variety of factors including the activity of the specific compound employed, the age, body weight, general health, sex, diet, time of administration, route of administration, rate of excretion, drug combination, and the severity of the particular disease undergoing therapy.

The combination of therapeutic agents of the present invention (as individual compositions or as a single composition) may be administered orally, parenterally, sublingually, by inhalation spray, rectally, or topically in dosage unit formulations containing conventional nontoxic pharmaceutically acceptable carriers, adjuvants, and vehicles as desired. Topical administration may also involve the use of transdermal administration such as transdermal patches or iontophoresis devices. The term parenteral as used herein includes subcutaneous injections, intravenous, intramuscular, intrasternal injection, or infusion techniques.

Injectable preparations, for example, sterile injectable aqueous or oleagenous suspensions may be formulated according to the known art using suitable dispersing or wetting agents and suspending agents. The sterile injectable preparation may also be a sterile injectable solution or suspension in a nontoxic parenterally acceptable diluent or solvent, for example, as a solution in 1,3-propanediol. Among the acceptable vehicles and solvents that may be employed are water, Ringer's solution, and isotonic sodium chloride solution. In addition, sterile, fixed oils are conventionally employed as a solvent or suspending medium. For this purpose any bland fixed oil may be employed including synthetic mono- or diglycerides. In addition, fatty acids such as oleic acid find use in the preparation of injectables.

Suppositories for rectal administration of the drug can be prepared by mixing the drug with a suitable nonirritating excipient such as cocoa butter and polyethylene glycols which are solid at ordinary temperatures but liquid at the rectal temperature and will therefore melt in the rectum and release the drug.

Solid dosage forms for oral administration may include capsules, tablets, pills, powders, and granules. In such solid dosage forms, the active compound may be admixed with at least one inert diluent such as sucrose lactose or starch. Such dosage forms may also comprise, as is normal practice, additional substances other than inert diluents, e.g., lubricating agents such as magnesium stearate. In the case of capsules, tablets, and pills, the dosage forms may also comprise buffering agents. Tablets and pills can additionally be prepared with enteric coatings.

Liquid dosage forms for oral administration may include pharmaceutically acceptable emulsions, solutions, suspensions, syrups, and elixirs containing inert diluents commonly used in the art, such as water. Such compositions may also comprise adjuvants, such as wetting agents, emulsifying and suspending agents, and sweetening, flavoring, and perfuming agents.

The combination of therapeutic agents of the present invention (as individual compositions or as a single composition) can also be administered in the form of liposomes. As is known in the art, liposomes are generally derived from phospholipids or other lipid substances. Liposomes are formed by mono- or multi-lamellar hydrated liquid crystals that are dispersed in an aqueous medium. Any non-toxic, physiologically aceptable and metabolizable lipid capable of forming liposomes can be used. The present compositions in liposome form can contain, in addition to the compound of the present invention, stabilizers, preservatives, excipients, and the like. The preferred lipids are the phospholipids and phosphatidyl cholines (lecithins), both natureal and synthetic.

Methods to form liposomes are known in the art. See, for example, Prescott, Ed., Methods in Cell Biology, Volume XIV, Academic Press, New York, N.Y. (1976), p. 33 et seq.

Preferred dosage forms for ritonavir include (a) a liquid dosage form for oral administration as disclosed in U.S. Serial No. 08/283 , 239, filed July 29, 1994 (now U.S. Patent No. 5,484,801, issued January 16, 1996 ), (b) an encapsulated solid or semi-solid dosage form as disclosed in PCT Patent Application No. WO95/07696, published March 23, 1995 and U.S. Serial No. 08/402,690, filed March 13, 1995 , both of which are incorporated herein by reference and (c) an encapsulated solid dosage form as disclosed in PCT Patent Application No. WO95/09614, published April 13, 1995 .

Claims (5)

1. A combination of ritonavir or a pharmaceutically acceptable salt thereof and a drug which is metabolized by cytochrome P450 monooxygenase 3A4, to improve the pharmacokinetics of the drug, provided that the drug is other than an HIV protease inhibitor.
2. A combination according to Claim 1, where ritonavir and the drug are formulated as a single composition.
3. A combination according to Claim 1, where ritonavir and the drug are formulated as separate compositions.
4. A combination according to any one of the preceding Claims, wherein the dose of ritonavir is from 0.001 to 300mg/kg body weight of the human to which it is to be administered.
5. A combination according to any one of the preceding Claims wherein the drug is cyclosporine, FK-506, rapamycin, taxol, taxotere or clarithromycin.