Comparative activity of mezlocillin, penicillin, ampicillin, carbenicillin, and ticarcillin against gram-positive bacteria and Haemophilus influenzae.

The in vitro activity of mezlocillin was compared to penicillin G, ampicillin, carbenicillin, and ticarcillin in tests with 195 gram-positive bacteria and 20 Haemophilus influenzae. Against gram-positive isolates excluding enterococci, penicillin was the most active drug, followed by ampicillin, mezlocillin, carbenicillin, and ticarcillin. Ampicillin was the most active of the five drugs against enterococci, whereas mezlocillin was the most active drug against 14 strains of ampicillin-susceptible H. influenzae.