An ongoing program of international generic antimicrobial potency assays for piperacillin/tazobactam has been summarized here through December 2010, and the initial results for meropenem generic lots from the United States are also presented. Fifteen additional piperacillin/tazobactam generic lots revealed an average of -10% activity (range, +3 to -23%) compared to the branded product (Zosyn®; Wyeth-Pfizer), a finding consistent with prior reports (46 lots) of -16%. In contrast, meropenem branded and generic products had equivalent assay results (5 generic lots from 2 manufacturers [Hospira and Sandoz]). In conclusion, potencies for generic lots of parenteral broad-spectrum β-lactams can vary widely when directly compared to branded products, requiring documentation by chemical, in vitro activity (potency assays as measured here), and purity testing before considering their addition to a hospital formulary.
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