Impurities used to 'fingerprint' fake medicines

analysisBelgian researchers have used the profile of impurities of tablets as 'fingerprints' to separate counterfeit from genuine medicines.

The team, from the country's Scientific Institute of Public Health and University Hospital of Liège, note that health problems caused by counterfeit medicines "are mostly due to this qualitative and quantitative variability in their formulation and impurity profiles."

Most counterfeit medicines are manufactured in non-Good Manufacturing Practice (GMP) conditions by uncontrolled or street laboratories, so the chemical composition and purity of raw materials may change in the course of time, according to the scientists.

The researchers looked at the impurity profiles of 73 samples of counterfeit copies of Pfizer's Viagra (sildenafil) and 44 fake samples of Eli Lilly's Cialis (tadalafil) using a high performance liquid chromatography system using ultraviolet detectors. They compared the illegal versions with 10 genuine Viagra and five genuine Cialis samples.

The technique was 100 per cent reliable in distinguishing illegal Viagra from genuine, and between 92 and 100 per cent effective for Cialis, depending on the classification algorithms used.

The team has published its work in the journal Analytica Chimica Acta (2011 Sep 9;701(2):224-31).

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