Comparison of actual and stated concentrations of pharmaceuticals manufactured in Mexico

During the past 5 years, there has been much concern about the safety of and ease of access to drugs that are unavailable without a prescription in the United States but are manufactured and can be purchased over the counter (OTC) in Mexico. However, based on a literature search, studies have not been performed to determine whether such drugs meet the US Pharmacopoeia (USP) standards for percent of labeled amount.

The aim of this study was to determine whether 5 drugs commonly prescribed in the United States and manufactured and purchased in Mexico met USP standards for stated concentration, were properly packaged and sealed, and had properly labeled expiration dates and lot numbers.

For the study, we purchased acetaminophen, carbamazepine, diazepam, digoxin, and phenytoin from 2 to 4 pharmacies in Ciudad Acuna, Mexico. Samples of each drug, each with a different lot number, were purchased OTC or with a prescription. None of the pharmacists had knowledge of the study. Brand-name or generic drugs manufactured and obtained in the United States were also analyzed for comparative purposes. Each drug was analyzed by high-performance liquid chromatography using USP guidelines established for the analysis of each drug. In addition, we visually examined the packaging, seals, color, and appearance of the drugs, and observed whether the packages contained lot numbers and whether the drugs were within the stated expiration dates.

For all 5 drugs, the 95% CIs fell within the USP-defined acceptable ranges for percent of labeled amount. This was found to be true for drugs obtained at different pharmacies, for different drug manufacturers, and for drugs with different lot numbers. All of the drugs were found to be properly packaged and sealed, had lot numbers listed on the packages, and were sold before the stated expiration dates.

Although health care practitioners should be aware that patients might be using drugs manufactured and purchased in Mexico, the results of this study of a small sample of such drugs suggest they meet the USP standards for percent of labeled amount.