Orally effective acid prodrugs of the .beta.-lactamase inhibitor sulbactam

Sulbactam (1) is a beta-lactamase inhibitor with limited oral bioavailability. Lipophilic double-ester prodrug sulbactam pivoxil (2) significantly improves the oral absorption of sulbactam, as does the mutual prodrug double ester sultamicillin (3). We have found that double-ester prodrugs of sulbactam terminating in a carboxyl group (8) also were effective oral-delivery vehicles in rats. Carboxyl-terminated double esters have several potential advantages over their nonionizable lipophilic counterparts, including water solubility, crystallinity, choice of salts for dosage forms, and formation of innocuous byproducts on hydrolysis.