Stable injectable paclitaxel composition

Abstract: A composition of taxol and polyethoxylated castor oil is pH balanced to have a pH less than 8.1 to improve stability. This composition can include an acid, preferably citric acid, to adjust the pH value. The invention includes a method of formulating a taxol solution for injection by mixing an acid with a carrier material, such as castor oil, to form a carrier solution after which taxol is mixed with the carrier solution to form the taxol solution at a pH of less than 8.1. The method may include the step of slurrying the taxol in alcohol before mixing with the carrier solution.

Description: This invention relates to a solution of paclitaxel having improved stability. BACKGROUND OF THE INVENTION Paclitaxel is a compound extracted from the bark of a western yew, Taxus brevifolia and known for its antineoplastic activity. It is described for example in The Merck Index, Eleventh Edition 1989, monograph 9049. In 1977, paclitaxel was chosen for development as an antineoplastic agent because of its unique mechanism of action and good cytotoxic activity against IP implanted D16 melanoma and the human X-1 mammary tumor xenograft. Paclitaxel is believed to function as a mitotic spindle poison and as a potent inhibitor of cell replication in vitro. Other mitotic spindle points (colchicine and podophyllotoxin) inhibit microtubule assembly. Paclitaxel employs a different mechanism of action since it appears to shift the equilibrium of polymerimization/depolymerization toward polymer assembly and to stabilize microtubules against depolymerization under conditions which would cause rapid disaggregation of microtubules. The interference with the polymerization/depolymerization cycle in cells appears to interfere with both the replication and migration of cells. After extensive preclinical screening in mouse tumour models, paclitaxel entered clinical trials in 1983. Over the past few years, paclitaxel has demonstrated good response rates in treating both ovarian and breast cancer patients who were not benefiting from vinca alkaloid or cisplatin therapy. It has also shown encouraging results in patients with other types of cancer including lung, melanoma, lymphoma, head and neck. For further information, reference may be made to the US National Cancer Institute's Clinical Brochure for Paclitaxel (Taxol®) revised July 1991, and papers presented at the Second National Cancer Institute Workshop on Taxol® and Taxus held in Alexandria, Virginia USA on September 23-24, 1992. BRIEF DESCRIPTION OF THE INVENTION It is a disadvantage of the known formulation that the paclitaxel therein degrades, with the result that the shelf life of the formulation is unsatisfactory, and there is therefore a need for a paclitaxel solution of improved stability. Accordingly, in a general aspect the invention provides a solution consisting of paclitaxel ethanol, polyethoxylated castor oil and acid, said solution having a pH of 5 to 7. The pH of the solution has been adjusted into the range 5 to 7 by addition of an acid. Accordingly, in another general aspect the invention provides a method of producing a paclitaxel solution according to the invention, said method comprising the addition of an acid to a solution consisting of paclitaxel, ethinol and polyethoxylated castor oil. Acids in the form of powders, for example citric acid, are preferred over those which contain water, for example sulfuric acid. The most preferred acid for use in accordance with the present invention is citric acid but a wide range of acids may be used including the following: Citric acid - monohydrous Citric acid - anhydrous Citric acid - hydrous Acetic acid Formic acid Ascorbic acid Aspartic acid Benzene sulphonic acid Benzoic acid Hydrochloric acid Sulphuric acid Phosphoric acid Nitric acid Tartaric acid Diatrizoic acid Glutamic acid Lactic acid Maleic acid Succinic acid DETAILED DESCRIPTION OF THE INVENTION Due to its limited solubility in water, paclitaxel is usually prepared and administered in a vehicle containing cremophor EL™ (a polyethoxylated castor oil which acts as a solubilizer) and ethanol. A commercially available solution supplied by Bristol-Myers Squibb (BMS) is formulated with these components and has a pH of 9.1. As indicated above, the invention essentially teaches addition of an acid to a paclitaxel formulation to adjust its pH into the range 5 to 7. In a preferred procedure adopted by the applicant, which it will be clearly understood is non-limiting, the following steps were carried out: Mixing Instructions SOLUTION 1 Citric acid was dissolved in absolute alcohol, using a ratio of 8mls of absolute alcohol to 1gram of citric acid, and the solution was stirred for fifteen (15) minutes. SOLUTION 2 Cremophor EL® was weighed out into the main mixing vessel. SOLUTION 3 Solution 1 was added to solution 2, and the container used for solution 2 was washed with a minimum quantity of absolute alcohol to ensure complete transfer of the citric acid. Solution 3 was mixed and bubbled with nitrogen for at least 15 minutes. The paclitaxel was weighed out and slurried using absolute alcohol, using a ratio of 8ml of absolute alcohol to 1gm of taxol. The slurried paclitaxel was added to solution 3 and the slurrying vessel was washed with a minimum quantity of absolute alcohol. Solution 3 was adjusted to 75% of required volume using absolute alcohol, and thoroughly stirred for at least 45 minutes until completely dissolved. Once completely dissolved, the volume was checked and made up as necessary with absolute alcohol and the final solution stirred for 5 minutes. Example 1 A solution was prepared with the following formulation: Formulation: (Sample 1) Cremophor EL® 0.5mL Citric Acid (Anhydrous) 2.0mg Paclitaxel 6.0mg Absolute Alcohol to 1.0mL The pH of this solution was determined as 6.1. The stability of this sample was compared with a sample prepared by the formulation stated in the NCI Taxol Clinical brochure (as follows) which had a pH of 9.1. (Sample 2) Sample 2 per mL Paclitaxel 6.0mg Cremophor El® 0.5mL Absolute Alcohol to 1mL The solutions were filled into clear type 1 glass 5mL vials and sealed with rubber bungs. The solutions were stored at 40°C for 7 (seven) days and the stability results are shown in Table 1. Sample 1 Sample 2 pH 6.2 9.0 Potency 96.6 86.7 Major individual 0.3% 5.1% impurity Total impurities 2.0% 12.2% Clearly Sample 1 showed significantly increased stability over Sample 2. Example 2 A solution was prepared with the following formulation: Formulation: (Sample 3) Cremophor EL® 0.5mL Paclitaxel 6.0mg Absolute Ethanol to 1mL pH adjusted to 6.6 with. 1.0M Acetic Acid. The solution was filled into clear type I glass 5mL vials and sealed with rubber bungs. The solution was stored at 40°C for 7 days. The stability results obtained are compared to those seen with Sample 2. Sample 3 Sample 2 pH 6.7 9.0 Potency 97.5 86.7 Major individual 0.3% 5.1% impurity Total impurities 2.3% 12.2% Again the significantly superior stability of the formulation according to the invention (Sample 3) is evident. It will be clearly understood that the invention in its general aspects is not limited to the specific details referred to hereinabove.

Claims: A solution consisting of paclitaxel, ethanol, polyethoxylated castor oil and acid, said solution having a pH of 5 to 7. The solution of claim 1 wherein said ethanol is absolute ethanol. The solution of claim 1 or claim 2 wherein said polyethoxylated castor oil is cremophor EL ™. The solution of any one of claims 1 to 3 wherein said acid is selected from the group consisting of citric acid, acetic acid, formic acid, ascorbic acid, aspartic acid, benzene sulfonic acid, benzoic acid, hydrochloric acid, sulphuric acid, phosphoric acid, nitric acid, tartaric acid, diatrizoic acid, glutamic acid, lactic acid, maleic acid, and succinic acid. The solution of claim 4 wherein said acid is citric acid. The solution of claim 5 wherein said citric acid is anhydrous or hydrous citric acid. The solution of claim 6 wherein said hydrous citric acid is monohydrous citric acid. A method of producing a paclitaxel solution as defined in any one proceeding claim comprising the addition of an acid to a solution consisting of paclitaxel, ethanol and polyethoxylated castor oil.

Inventors: CARVER DAVID R, ELLIOTT ROBYN, EWALD HERNITA, HANDRECK PAUL, PROUT TIMOTHY R, CARVER, DAVID R., ELLIOTT, ROBYN, EWALD, HERNITA, HANDRECK, PAUL, PROUT, TIMOTHY R.
Applicants: MAYNE PHARMA USA INC, MAYNE PHARMA (USA) INC.
Application year: 1993
Main classification: A61K31
IPC codes: A61K47, A61K9, A61K31