In vitro potency evaluations of various piperacillin/tazobactam generic products compared with the contemporary branded (Zosyn®, Wyeth) formulation

Twenty-three generic intravenous piperacillin/tazobactam products were compared for in vitro activity to the branded formulation (Zosyn®, Wyeth, Philadelphia, PA) by disk diffusion and incremental broth microdilution assay methods. All but 1 lot demonstrated significantly decreased activity (−5 to −35%), necessitating further investigations regarding the chemical purity, potency, and therapeutic equivalence of these products worldwide. The average −16% activity across all generic lots was equivalent to underdosing piperacillin/tazobactam by 2.6 g daily for serious clinical infections (4.5 g Q6 h).