In vitro activity of piperacillin/tazobactam against isolates from patients enrolled in clinical trials

The in vitro activity of piperacillin alone or titrated with a constant concentration of 4 mug/ml tazobactam was evaluated against 3962 baseline pathogens isolated from 1899 patients enrolled in 9 clinical trial studies in North America. Tazobactam increased susceptibility rates of piperacillin for Enterobacteriaceae from 81% to 96%, Staphylococcus (methicillin susceptible) spp. from 6% to 100%, Bacteroides fragilis group from 79% to >99% and Haemophilus from 85% to 98%. The excellent activity of piperacillin against Pseudomonas, Streptococcus and Enterococcus was maintained in the presence of tazobactam. Overall piperacillin/tazobactam had better activity than ticarcillin/clavulanic acid, ceftazidime, and in general equaled the activity of imipenem. The excellent in vitro, extended-spectrum activity of piperacillin/tazobactam suggests its utility for various infections.