Penicillin in oil-wax mixtures.

One of the main disadvantages of penicillin as a chemotherapeutic agent is that the kidney is able to eliminate it from the blood in a relatively short time, making it necessary that injections be repeated fairly frequently in order to maintain a therapeutic blood level for a long period. This is, of course, most undesirable from the patient's point of view and many workers have attempted to find means whereby the n'umber of injections per twenty-four hours could be lessened. The most promising method so far developed to this end is that introduced by Romansky and Rittman (1944), who incorporated the penicillin in a mixture of peanutoil (arachis oil) and beeswax. This mixture had the property, when injected into the body, of giving a slow release of penicillin, with consequent prolongation of detectable blood levels and therefore a reduction of the number of injections required. Romansky concluded that the optimum results were obtained with a mixture containing 4-8 per cent. beeswax in arachis oil with a maximum penicillin concentration of 300,000 u/ml., the penicillin having a potency of not less than 1,000 u/mg. However, the use of Romansky's preparation is not without difficulties, for at room temperature this mixture is solid and it requires heating to a teniperature between 400 and 500 C. to be melted. Even then the bore of the needle needed for injecting it is large and somewhat uncomfortable for the patient. The difficulty of heating the preparation before use is easily overcome in hospital practice where all facilities are present, but the position is often quite different for the general practitioner attending a patient in his own home. The difficulties inherent in the use of Romansky's preparation led to the search for other preparations which would give a similar prolongation of penicillin blood levels but which would be fluid at room temperature and would pass through a relatively fine-bore needle. Of such preparations the ones giving the most encouraging results to date have been mixtures of beeswax in ethyl oleate, which are fluid at room temperature and can be injected through a finer-bore needle than that required for Romansky's preparation. It has been said, however, that the beeswax-ethyl-oleate mixtures do not give such prolonged penicillin blood levels as beeswax and arachis oil, and the object of the present investigation, carried out on behalf of the Ministry of Health, has been to compare the penicillin blood levels obtained with beeswax mixed with ethyl oleate on the one hand and arachis oil on the other.