Carbenicillin: activity in vitro and absorption and excretion in normal young men.

Carbenicillin is a new semisynthetic penicillin which differs from other penicillins in showing moderate antibacterial activity against Pseudomonas. Its activity in vitro is enhanced at low pH. Serum binding is of low order and does not appreciably alter activity. Strains of Pseudomonas exposed to subinhibitory concentrations of carbenicillin rapidly develop resistance by a mechanism that does not depend upon destruction of the drug. In normal subjects, high levels of anti-Pseudomonas activity are readily obtained in the urine after intramuscular injection. Levels of carbenicillin adequate to inhibit many strains of Pseudomonas can be achieved in serum only with an intravenous administration of a large dose. Carbenicillin appears to exhibit the same low degree of toxicity as do other penicillins.