Clinical effectiveness of generic vancomycin products compared to Vancocin CP® in patients with methicillin-resistant Staphylococcus aureus infections: A retrospective cohort

Abstract

Introduction: Approval of generic drugs requires only bioequivalence studies. Some research suggests that generic vancomycin is not clinically equivalent to the branded drug, and this exposes patients to therapeutic failure and the development of microbial resistance.
 Aims: Compare the rates of microbiological and clinical failure between generic vancomycin and Vancocin-CP®.
 Methods: Retrospective cohort analysis of hospitalized adults with culture-proven methicillin-resistant Staphylococcus aureus infection, treated with vancomycin in a tertiary care hospital in Medellín, Colombia. General clinical variables, laboratory findings, severity and mortality scores, and type of vancomycin used were recorded. Logistical regression models, adjusted for potential confounders, were fitted to estimate the effect of vancomycin on clinical and microbiologic outcomes.
 Results: Of 209 patients, 153 (73.2%) received generic vancomycin and 56 (26.8%) Vancocin-CP®. Systems more commonly affected were skin and soft tissues (28.5%), blood with involvement of catheters (27.6%) and blood without the involvement of catheters (23.3%). There were 62 clinical failures (29.5%) and 41(38%) microbiological failures. The hospital mortality rate was 15% (n = 31); only 7 (3.4%) episodes of adverse drug reactions were documented. No difference was found in the risk of clinical or microbiological failure between Vancocin-CP® and generic products with OR = 2.3 (95% CI = 0.8; 6.3) and 0.89 (95% CI = 0.4; 1.9), respectively. 
 Conclusion: There were no association between the use of generic vancomycin and the outcomes of clinical or microbiological failure. Sample size is an important limitation for these findings.
 
 Keywords: Vancomycin, bioequivalence, MRSA, clinical equivalence