Intramuscular injections and muscle damage: effects of concentration, volume, injection speed and vehicle.

An intramuscular injection was given to rabbits with the needle inserted in the longissimus dorsi muscle. The muscle tissue at the injection site was examined post-mortem 3 days after the injection and areas of necrotic muscle tissue were dissected for weighing. With a fixed dose of the neuroleptic drug cis(Z)-clopenthixol it was shown that a small volume of a concentrated solution caused less muscle damage than a larger volume of a relatively less concentrated solution. Injection speed, on the other hand, was not an important factor. Aqueous solutions of neuroleptic drugs caused local muscle damage which was diminished or prevented by oily vehicles.