Possible Carcinogen Found in Pfizer’s HIV Drug, FDA Says

Pfizer issued a letter to healthcare professionals advising them of a potential human carcinogen in its HIV drug Viracept, the FDA announced.

The levels of ethyl methanesulfonate (EMS) found in Pfizer’s batches of Viracept (nelfinavir mesylate) were substantially lower than those found earlier this year in Viracept products manufactured by Roche, which prompted Roche to recall the drug from all European Union markets, Pfizer said.

Data from animal studies indicate EMS is carcinogenic and may cause cancer and birth defects, but there is no data from humans, Pfizer and the FDA said. The company added it is continuing to test its Viracept products and has agreed on interim and long-term EMS specifications with the FDA. Only products meeting the specifications will be released for patient use, the company said.

The interim specification limits the theoretical lifetime increased cancer risk in adults to fewer than 17 cases per 100,000 people exposed, Pfizer said. The long-term specification limits the theoretical lifetime increased cancer risk in adults to fewer than one case per 100,000 people exposed.

Pregnant women and pediatric patients who are starting HIV treatment should not start regimens with Viracept until further notice, the FDA and Pfizer said. However, pediatric patients who are currently taking the drug may continue to take Viracept, they said. Pregnant women taking the drug should be switched to an alternative treatment if possible, they added.  

There is no change in the recommended use of Viracept for all other patients, Pfizer said.

Pfizer’s letter to healthcare professionals can be seen at www.fda.gov/medwatch/safety/2007/VIRACEPT_
HCPLetter_9_10_07.pdf