Carbenicillin is a semi-synthetic ampicillin analog, and like ampicillin is a beta-lactam antibiotic. Carbenicillin is a member of the carboxypenicillin subgroup of the penicillins.
It is effective against Gram-negative organisms including H. influenzae and E. coli. Carbenicillin is also used in transformed Agrobacter species. Carbenicillin was the first penicillin with significant activity against Pseudomonas species.