Antimicrobial Compositions

This invention relates to tetracycline-based compositions for the treatment of microbial infections. The antibacterial activity of the tetracyclines is well known, but improved stability could be advantageous particularly in contact with air, particularly when in solution in water. Antimicrobial compositions comprising tetracycline in a variety of common pharmaceutical carriers, with improved shelf life particularly of opened and part-used product forms, e.g. multiple pack of impregnated wound dressings, would be of real use to the medical profession.

The present invention provides an antimicrobial composition comprising a tetracycline in a concentration to have an effective antibacterial action, 8-hydroxyquinoline or a chlorinated and/or alkyl derivative thereof in a concentration to stabilise the tetracycline, and a pharmaceutically acceptable diluent and/or carrier. Both the tetracycline and the quinoline derivative may be present as such or in the form of a salt.

By a tetracycline is meant a member of the class of antibiotics broadly known as tetracyclines such as tetracycline, oxytetracycline, chlortetracycline, dimethylchlortetracycline, doxycycline, methacycline and their salts such as hydrochlorides. The concentration of tetracycline to provide an effective antimicrobial action depends on the circumstances of use, but will often be in the range of 0.1% to 6%, preferably 1% to 3%, by weight on the weight of the composition.

As stabilising agents, there are particularly envisaged 8-hydroxyquinoline, 5-chloro-8-hydroxyquinoline, 5,7-dichloro-8-hydroxyquinoline, 5,7-dichloro-8-hydroxyquinaldine, their salts such as hydrochlorides and sodium salts, and mixtures thereof. The concentration required to stabize the tetracycline, by retarding or preventing decomposition thereof, again depends on the circumstances of use, but will often be in the range of 0.1% to 8%, particularly 1 % to 3%, by weight on the weight of the composition. 8-Hydroxyquinoline itself is somewhat toxic compared to its chlorinized derivatives and is likely to be used in concentrations only towards the lower ends of these ranges. 5-chloro-7-iodo derivatives of 8-hydroxyquinoline may also be useful in cases where any liberated iodine does not accelerate decomposition of the tetracycline.

Preferably the ratio of the tetracycline to the 8-hydroxyquinoline or chlorinated and/or alkyl derivative thereof is between 3:1 and 1:3 by weight.

The compositions of this invention may be used for topical application to wounds, burns, ulcers, and topical infection, or for oral administration to combat internal infection.

In the treatment of surface wounds it is known that tetracyclines produce a good effect against a wide range of bacteria but that there is the possibility of contamination of the wound by mould spores or organisms resistant to tetracyclines. Such wounds as road accident abrasions are known to be very highly contaminated and have proved to be quite a problem as regards treatment with antibiotics. It has now been found that the incorporation of 5-chloro-8-hydroxyquinoline and other related 8-hydroxyquinolines into topical formulations with tetracycline, results in a product having, not only improved storage stability, but also synergistic activity against a wide spectrum of microorganisms.

A preferred composition for such purposes comprises from 1% to 3% by weight of tetracycline, from 1% to 3% by weight of 5-chloro-8-hydroxyquinoline and a pharmaceutically acceptable diluent or carrier.

Compositions for internal application preferably comprises 5,7-dichloro-8-hydroxyquinoline as the stabilising agent.

8-Hydroxyquinoline and 8-hydroxyquinaldine derivatives are amphoteric and may therefore under some circumstances form salts with the tetracycline. It is believed, however, that the two active ingredients act separately, and that any salt formation that may take place does not adversely affect the antimicrobial properties of the composition.

The compositions may be prepared in the form of ointments, creams, lotions, passaries, powders and also spray pack formulations containing the active ingredients in solution or suspension.

The composition in the form of an ointment usually utilises a non-aqueous base material such as petrolatum. Such compositions in the form of ointments may be employed in the production of medicated dressings where a tulle prepared from say bleached cotton, cotton and rayon, or rayon is impregnated with the ointment.

For the treatment of oral infections and wounds such as ulcers where the composition may be in the form of an ointment, powder or lozenge the composition may also include suitable flavouring agents.

The compositions may also include anti-inflammatory drugs which are active when applied topically such as hydrocortisone. They may also include antioxidants such as sodium metabisulphite.

The invention is illustrated by the following non-limiting examples

A topical ointment was prepared having the following composition

A topical ointment was prepared having the following composition

A formulation having the following composition was prepared and used to impregnate a tulle:

A topical gel was prepared having the following composition

A sterile dusting powder was prepared having the following composition

5,7-dichloro-8-hydroxyquinaldine can be used in place of 5-chloro-8-hydroxyquinoline.

A product for application in the form of an aerosol spray was prepared by filing into a 2 oz. aerosol container a concentrate containing

and then pressurizing the container by the addition as propellant of a mixture

A powder in a form suitable for topical ulcer application was prepared having the following composition

Mouth lozenges were prepared each lozenge having the composition:

Pessaries were prepared, each pessary having the composition:

The antimicrobial activity and storage properties of the ointment of Example 1 (containing 1% tetracycline hydrochloride and 1% 5-chloro-8-hydroxyquinoline) was compared with a similar ointment containing 1% tetracycline hydrochloride.

Surprisingly it was found that the ointment (A) containing 1% tetracycline hydrochloride and 1% 5-chloro-8-hydroxyquinoline was rather more stable than the ointment (B) containing 1% tetracycline hydrochloride alone. Thus visual examination of samples stored in the absence of light for three months and six months at room temperature, 37.degree. C. and 45.degree. C. showed only slight colour change with the former but severe darkening with the latter.

Again on storage there was no evidence of evolved gases with the former ointment after storage at room temperature, 37.degree. C. or 45.degree. C. for three or six months whereas with the latter after storage at room temperature for three or six months there was a slight odour, and with samples stored for three or six months at 37.degree. C. or 45.degree. C. there was a strong odour.

The samples of ointment (A) and (B) stored at elevated temperatures for six months were examined by thin layer chromatography using cellulose plates. One gram samples of the ointments were washed with petroleum ether (b.p. 40.degree.-60.degree. C.) thus removing the 5-chloro-8-hydroxyquinoline and the jelly base and leaving as a residue the tetracycline and any of its breakdown products. The residue was taken up in methanol (2 mls) chloroform (2 mls) and water (10 drops) and fractionated on cellulose preparative thin layer chromatography plates eluting with ethyl acetate/isopropanol/water (70:40:20). The main breakdown product from the sample of ointment (B) stored at 37.degree. C. and 45.degree. C. was extracted from the plates and found to be equivalent to 5% and 8% respectively of the tetracycline. In these two samples of ointment (B) there was also a minor proportion of a second breakdown product. With the ointment (A) the evidence was that breakdown if any was negligible.

The microbiological properties of ointment (A) were compared with those ointments (B) and an ointment (C) (containing 1% 5-chloro-8-hydroxyquinoline) against a range of organisms isolated from clinical conditions.

Two tests were used to detect any bacteriostatic properties of the formulations.

Pour plates were prepared, using 20 ml. nutrient agar containing 0.4 ml. culture. Plates were prepared for each culture tested. A well was cut in the centre of each plate which was then filled with the jelly under test. The plates were incubated at 37.degree. C./48 H. Clear zones of inhibition which had developed were measured.

5g of jelly were added to 95 ml. nutrient broth and the mixture left overnight in an incubator at 37.degree. C. This was done in order to improve the dispersion of the jelly in the nutrient broth and hence allow the antibiotic to deffuse into the liquid medium. At ambient temperature the jelly was completely immiscible in the broth.

The following day doubling dilutions of this 1:20 dilution were made to a final dilution of 1:10,240 i.e. a total of 10 dilutions were made in all.

Each dilution was incubated with 1 drop of 1 in 10 dilution of a 24 h. broth culture of organism under test and the tubes incubated at 37.degree. C./72 h.

The minimum inhibitory concentration (MIC) of the jelly was the highest dilution which failed to allow growth of the organism.

From the MIC results and Zone inhibiton results given in the table below, there is some evidence of synergism between the two agents against certain organisms, e.g. Staphylococcus albus, E. coli, some Proteus spp. and Klebsiella aerogenes.

A 1% by weight solution of tetracycline hydrochloride in water was divided into three parts. To the first part there was added 1% by weight of 5-chloro-8-hydroxyquinoline. To the second part there was added 1%, by weight of 5,7-dichloro-8-hydroxyquinoline. No addition was made to the third part. The three aqueous compositions were then stored at 37.degree. C. in air. Decomposition of tetracyline in the third part was quite rapid, and a brown colour developed within a week. The other two parts showed good stability after one weeks storage. It appears that the decomposition of tetracycline in aqueous solution is materially slowed down in the presence of chlorinated derivatives of 8-hydroxyquinoline.

In the Examples:

Polyox W S R - 205 is believed to be a polyoxyethylene glycol.

Natrosol is a hydroxyethylcellulose.

A 1% by weight solution of oxytetracycline hydrochloride in water was divided into two parts. To the first part was added 1% by weight of 5-chloro-8-hydroxyquinoline. No addition was made to the second part. The two aqueous compositions were then stored at 37.degree. centigrade in air. Decomposition of the oxytetracycline in the second part was quite rapid and a brown colour developed within a week. The other part showed good stability after one week's storage.

A 1% by weight solution of chlortetracycline hydrochloride in water was divided into two parts. To the first part was added 1% by weight of 5-chloro-8-hydroxyquinoline. No addition was made to the second part. The two aqueous compositions were then stored at 37.degree. C. in air. Decomposition of the chlortetracycline hydrochloride in the second part was quite rapid and a brown colour developed within a week. The other part showed good stability after one week's storage.

A 1% by weight solution of tetracycline hydrochloride in water was divided into two parts. To the first part was added 0.5% by weight of 5-chloro-8-hydroxyquinoline. No addition was made to the second part. The two aqueous compositions were then stored at 37.degree. C. in air. Decomposition of the tetracycline hydrochloride in the second part was quite rapid and a brown colour developed within a week. The other part showed good stability after one week's storage.