A Comparison of Pharmaceutical Products Obtained from the United States and Mexico

Abstract

Objectives: Despite the growing attention to the issue of patient utilizing foreign pharmaceuticals, the lack of scientific evidence makes it impossible to reach a conclusion about the topic. The objective of this study was to test the content of the active ingredient in three medications (warfarin, levothyroxine, and Viagra/sildenafil), obtained from the United States and Mexico, according to United States Pharmacopeia (USP) standards. Methods: The identification and quantification of the pharmaceutical products was determined utilizing normal and reversed phase high-performance liquid chromatography (HPLC). Each individual tablet was weighed , dissolved in an appropriate solvent, and sonicated to produce a sample for HPLC analysis. Twenty, ten, or six individual samples of each medication were analyzed twice via an appropriate HPLC method, depending on the number of tablets available. In addition, a bulk sample of twenty tablets was analyzed for both warfarin and levothyroxine to assess an average concentration for each sample. Results: The content of levothyroxine in the three Mexico medications was 87.0±2.3%, 104.7±3.1%, and 100.5±14.2%; compared to 98.4±1.4% in the US sample. Warfarin content analysis for the Mexican products resulted in an average of 98.5±2.6%, 95.9±1.1% and 94.8±1.8%; compared to 97.4±2.3% in the US sample. The sildenafil samples from Mexico were found to contain only 67.8±3.8% and 71.1±1.0% of what the US sample contained. Conclusions: Six out of the eight samples collected from Mexican pharmacies contained lower amounts of active ingredient than their US equivalents. In terms of the average concentration, many of the medications from Mexico fell within the USP range but there was great variation in the content of each individual tablet.