Half of sildenafil samples purchased on the internet were fake

Sep 27 2004

Around half of the Viagra samples purchased on the Internet were counterfeit, according to researchers who are today announcing a new technique that detects counterfeit medicines at the British Pharmaceutical Conference.

According to Dr Nic Wilson, from the School of Pharmacy, University of London, the novel use of a technique called near infrared (NIR) microscopy offers a new sophistication to the identification of fake pharmaceuticals by providing a detailed picture of what is in a tablet.

NIR microscopy produces an ‘image map’ made up of thousands of spectra from a tablet sample. From this, it is possible to identify the components of the tablet, both active ingredients and inert ingredients, and the amount of each component. Particle size and distribution within the tablet, another clue to the tablet’s origin, can also be determined.

NIR microscopy provides more information than the established technique of ‘NIR spectroscopy’. “It gives another layer of information,” Dr Wilson said. “For example, a counterfeit tablet may contain lactose as an ingredient in the tablet bulk, whereas the authentic tablet does not. NIR spectroscopy could only show that the tablets are different, while NIR microscopy could actually identify the likely presence of lactose.”

For the moment, the researchers are concentrating on Viagra. This drug is widely available over the Internet and, like other ‘lifestyle’ drugs, it is a major target for counterfeiters.

Dr Wilson has tested the new technique using known counterfeit tablets. Most were found to contain less of the active ingredient ‘sildenafil’ than bona fide Viagra. The researchers then obtained samples of Viagra from the Internet and analysed them. “On our initial estimate, around half of these Viagra samples could be counterfeit,” commented Dr Wilson. The samples are now being analysed by Pfizer (manufacturer of Viagra) using existing methods of analysis, which the researchers expect will support their findings.

The counterfeit medicines were also shown to contain different ingredients from those in the authentic tablet. “We don’t know that ‘wrong’ components will be harmful, but the user runs the risk of poor quality and possible toxicity, not to mention the fact there is a high probability that the tablets may have no clinical effect,” said Dr Wilson.

Ultimately, it could be possible to use this technology to track counterfeit products across the world. Dr Wilson explained: “Once counterfeit tablets have been identified their images can be added to a database. When other suspect tablets are seized and later identified as fakes, they can then be compared with the known counterfeits present in the database. The identity of the components in the newly identified counterfeits and their distribution within the tablet can be compared with those in the database.

“This will help to link different sources of counterfeit tablets and to monitor the movements of batches of counterfeit tablets. It will therefore help the regulatory authorities and the pharmaceutical companies in the fight against the counterfeit medicine trade.”

Dr Wilson’s work is funded by a Maplethorpe Fellowship from the University of London. She is working in collaboration with the Medicines and Healthcare products Regulatory Agency and Pfizer.

The Royal Pharmaceutical Society of Great Britain (RPSGB) is the regulatory and professional body for pharmacists in England, Scotland and Wales. The primary objective of the RPSGB is to lead, regulate and develop the pharmacy profession.