Local tolerance of i.m. mezlocillin injection.

To evaluate the intensity of the localized pain caused by intramuscular administration of 6-[(R)-2-[3-methylsulfonyl-2-oxo-imidazolidine-1-carboxamido]-2-phenyl-acetamido]-penicillanic acid sodium salt (mezlocillin, Baypen), the pain was compared to that caused by ampicillin in a blind test. Ampicillin served as reference because of its extensive use. 50 patients were given 1 g of mezlocillin and 1 g of ampicillin successively, in both gluteal regions. Ampicillin is significantly more painful than mezlocillin. However, substantial pain is produced by both drugs. In a second study, to reduce the pain, 50 patients were given 1 g of mezlocillin twice, one injection was given in a period of 5-7 s, and the other in a 12-15 s period. The slower injection is significantly less painful than the faster one. In conclusion, i.m. administration of mezlocillin is less painful than that of ampicillin, and the slow injection reduces the pain of mezlocillin administration.