A comparison of the effects of mezlocillin and carbenicillin on haemostasis in volunteers.

Mezlocillin and carbenicillin were administered intravenously to healthy male volunteers, for six days each, in a double-blind crossover study. Tests to detect abnormalities in haemostasis were performed before, during and after administration. Platelet aggregation studies indicated that both antibiotics interfered with platelet aggregation and secretion resulting in prolonged bleeding times. The effect was dose related and rapidly reversible after discontinuation of the antibiotics. It always occurred earlier and was more profound with carbenicillin than with mezlocillin (P = 0.008). Bleeding times greater than 15 min were observed in 17% of volunteers who received 18 g/day of mezlocillin and 83% of volunteers who received 18 g/day of carbenicillin (P less than 0.05). There were no abnormalities in the coagulation cascade. The risk of acquiring an antibiotic-induced clinical bleeding disorder is lower with mezlocillin than with carbenicillin.