Tigemonam is a monobactam, with potent activity against Gram-negative aerobic bacterial pathogens. Tigemonam (0.25 mg/L) inhibits 90% of Escherichia coli, Klebsiella spp., Proteus spp., Salmonella spp., Haemophilus influenzae and Branhamella catarrhalis tested. The MIC90 for Enterobacter spp. is 16 mg/L and for Citrobacter 4 mg/L. Pseudomonas aeruginosa is resistant to tigemonam but susceptible to aztreonam. Tigemonam shows minimal inoculum dependence, between 102 and 106 cfu per spot. Tigemonam shows potent activities against Escherichia coli SC 8294, E. coli SC 12199, Salmonella schottmulleri SC 3850, Proteus mirabilis SC 9575, Providencia rettgeri SC 8217, Klebsiella pneumoniae SC 12216, Serratia marcescens SC 9782, Enterobacter cloacae SC 11078, Haemophilus influenzae SC 10556, with ED50 of 1.4 mg/kg, 1.5 mg/kg, 0.7 mg/kg, 0.3 mg/kg, 0.2 mg/kg, 0.9 mg/kg, 0.5 mg/kg, 3.9 mg/kg and 1.8 mg/kg in mice.