Local toxicity of different drugs after intramuscular or intralipomatous injection in pigs: serum concentrations after three different formulations of cis(Z)-clopenthixol.
Findings made by computerized tomography scanning of pelvis of patients suggested that the majority of injections intended to be intramuscular in fact are delivered in the fat tissue. This finding has raised the question what difference it makes when drugs are injected intramuscularly or intralipomatously. We have studied local toxicity after intramuscular or intralipomatous injection of different drugs in pigs, which have a subcutaneous layer of fat comparable to that of man. The pigs were killed 1, 3, 7 or 14 days after injection of antibiotics, vitamins, neuroleptics, diazepam, digoxin, pentazocine, sulphadimidine and vehicles. The tissues at the injection site were examined macro- and microscopically. In another series of experiments an aqueous or two different oily preparations of the neuroleptic drug cis(Z)-clopenthixol were given intramuscularly or intralipomatously to pigs and a series of blood samples were taken for drug level determination. The tissue examinations showed that all drugs causing local muscle damage after intramuscular injection caused considerably less extensive damage with a faster regeneration after intralipomatous injection. The pharmacokinetic study showed that there was virtually no difference between plasma-concentration-time curves after intramuscular or intralipomatous injection. Our findings indicate that intralipomatous injection of irritating drugs is better tolerated than intramuscular injection since intralipomatous injection causes less local toxicity. Our findings also suggest that the pharmacokinetics are not different. However, further studies are required to substantiate whether the findings are of general relevance.