Determination of Therapeutic Equivalence (TE) of 5 Generic Products (GP) of Penicillin G (PEN) Using the Neutropenic Murine Thigh Infection Model (NMTIM)

Abstract

ABSTRACT: Background: Legal use of GP in human and veterinary medicine has great impact in price regulation worldwide, but numbers of GP makers are increasing overwhelmingly. Beyond quality problems, concern is growing about the scientific basis of using bioequivalence (BE) as surrogate proof of TE, the accepted dogma. To test it, bactericidal efficacy of GP of PEN made in Colombia was compared in vitro and in vivo against the original compound (OC) in simultaneous experiments, employing the same methods required for new antimicrobials. Methods: Microbiologic assays with S. aureus ATCC 6538p and broth microdilution minimal inhibitory and bactericidal concentrations (MIC/MBC) were used to determine BE by comparison of standard curves (SC) and in vitro activity. The NMTIM used 6 week-old specific pathogen free ICR:CD-1 female mice weighting 25±2 g infected with S. aureus GRP-0057, a PEN-susceptible clinical isolante. The sigmoid dose-response model was applied to calculate by least squares nonlinear regression (NLR) pharmacodynamic parameters (PDP) like Emax and bacteriostatic dose (BD). SC were compared by linear curve fitting analysis (CFA), whole NLR by nonlinear CFA, individual PDP by nonlinear CFA and Wilcoxon-Mann-Whitney test (WMW), MIC/MBC by WMW. Results: All 5 GP were made in Colombia; 1 had greater amounts of PEN (intercept = 0.0052 vs 0.0041 mg/l, P<0.0001), but did not differ in MIC/MBC from the OC. Only 1 of the other 4 GP had lower MIC/MBC, 0.01/0.02 vs 0.07/0.10 mg/l for the OC (P = 0.013). Mice had 104.49-4.74 CFU/thigh (CFU/g) when treated with PEN 0.094-24 mg/kg for 24 hours (24h) divided q1h. At the end of therapy, untreated controls had 107.65-7.83 CFU/g (24h growth = 2.92-3.33 log10 CFU/g). All 5 GP failed TE: Emax = 2.01-3.26 vs 4.87 log10 CFU/g, and BD = 6.94-120.1 vs 1.65 mg/kg/24h for GP and OC respectively (P<0.0005). Conclusions: GP of PEN do not exhibit TE with the OC. Current criteria for BE and TE deserve review.