Ampicillin-sulbactam and ticarcillin-clavulanic acid: a comparison of their in vitro activity and review of their clinical efficacy.

Sulbactam (SB) and clavulanic acid (CA) are irreversible inhibitors of the beta-lactamases in the Richmond and Sykes classes II-VI. When combined with ampicillin and ticarcillin, SB and CA, respectively, extend the spectrum of activity of these penicillins to include some beta-lactamase-producing aerobes (Enterobacteriaceae, Hemophilus influenzae, staphylococci) and anaerobes (Bacteroides fragilis group) which would otherwise be resistant. Neither effectively inhibits the class I beta-lactamases frequently produced by Pseudomonas aeruginosa, Enterobacter, and Serratia, in part explaining the resistance observed with these organisms. Clinically, both agents were as effective as the comparative therapies in all but two of the trials reviewed. Given the current data, the decision to add these agents to the formulary should be based on hospital resistance patterns and on the cost of these antimicrobials in comparison to conventional therapies.