Roche informed the European Medicines Agency (EMEA) of its findings late on Tuesday, and efforts are being made across European Union markets to recall the tainted drug as quickly as possible before patients are harmed. Roche was alerted to the possible contamination by patients themselves, who reported that the company's 250mg tablets had a strange smell. After investigating the complaints, Roche discovered that the tablets contained unexpected high levels of ethyl mesylate, a potentially harmful chemical also known as methane sulfonic acid ethylester. This contaminant is a well-known genotoxic substance (i.e. harmful to DNA) and can cause cancer or harm unborn children if used during pregnancy. The contamination is believed to be related to the manufacture of the Viracept active substance nelfinavir itself, and thus may have affected all forms and strengths of the drug - hence Roche's immediate recall of all packs in the EU. Although early tests have shown that the level of contamination between products and batches may vary, a total recall was seen as the best way to ensure patient safety. The alert covers all Viracept products, irrespective of whether they were supplied directly from Roche or through parallel distribution. According to an EMEA spokesperson, the contaminated tablets are believed to have been manufactured in Switzerland with the batch release occurring in Spain. Roche has emphasised the fact that although recalls have been initiated in all 27 member states, Iceland, Lichtenstein and Norway, the US, Canada and Japan are not affected by the recall. Viracept is currently available as an oral powder, in 50mg and 250mg tablets, and 250mg film-coated tablets. Although the EMEA was unable to put a figure on how many packs of Viracept would have to be recalled, the Medicines and Healthcare products Regulatory Agency (MHRA) has put the number of patients currently prescribed the drug in the UK at around 550. "Our main priority is public safety," a spokesperson for the agency said, "so we are using outlets such as the media to alert the public to the potential safety risks that have been associated with this drug." The MHRA has highlighted that it has "special concerns" regarding the Viracept as it may be used in children and pregnant women who are at high risk of suffering the harmful effects of the toxic substance, let alone the vulnerability of the HIV population as a whole. Viracept is a protease inhibitor first introduced by Roche in 1998. It works by blocking an enzyme (protease) that is involved in the production of HIV, which then prevents the virus reproducing normally subsequently slowing the spread of infection. Although details regarding the contamination case appear to be closely guarded by the manufacturer, with the European representative for Viracept unable to disclose any information, the EMEA "hopes to be getting further information from Roche" as it becomes available.