Comparative in-vitro activity of temocillin (BRL 17421), a new penicillin

The activity in vitro of the new parenteral penicillin, temocillin, was determined by an agar dilution technique at two inocula against 201 recent clinical isolates and also against reference strains that produced characterized beta-lactamases. Ampicillin, ticarcillin, latamoxef (moxalactam) and cefoxitin were used as comparative agents. Temocillin showed no useful activity against Pseudomonas aeruginosa or the Bacteroides fragilis group but was highly active against the Enterobacteriaceae, inhibiting all isolates (Serratia marcescens excepted) at less than or equal to 8 mg/l. The MIC50 and MIC90 were usually within one dilution and results with both inoculum sizes were similar. Temocillin also had good activity against Haemophilus influenzae and beta-lactamase producing strains were as susceptible as non-beta-lactamase producers. Neither for the Enterobacteriaceae nor for H. influenzae did a 1000-fold increase in inoculum result in a greater than two-fold increase in MIC. The above results implied excellent stability to beta-lactamases and this was borne out by the activity of temocillin against strains containing chromosomal cephalosporinases, the 'broad-spectrum' Class IV enzyme and the plasmid mediated enzymes TEM-1, OXA-1 and SHV-1. The protein binding of temocillin was found to be 87%.