Tigemonam is a dialkylazetidinone derivative patented by E. R. Squibb and Sons, Inc. as a beta-lactam agent useful for the treatment of bacterial infections. Of the orally active beta-lactams, tigemonam is one of the most potent, with a spectrum of activity similar to that of aztreonam and highly resistant to hydrolysis by the beta-lactamase enzymes. Tigemonam inhibits 90% of Escherichia coli, Klebsiella spp., Proteus spp., Salmonella spp., Haemophilus influenzae and Branhamella catarrhalis tested. In localized infections, tigemonam also demonstrated excellent in vivo activity. In acute pyelonephritis in mice caused by Escherichia coli or Proteus sp., tigemonam was very effective. In a rat lung model with Klebsiella pneumoniae, tigemonam was active with a median effective dose of 46 mg/kg compared with 160 mg/kg for cefaclor and over 200 mg/kg for amoxicillin.