FDA, Pfizer Warn of Possible Carcinogen in Antiretroviral Treatment Viracept
Tests have detected a "potential human carcinogen" in batches of Pfizer's antiretroviral drug Viracept, FDA and the pharmaceutical company announced Monday, Reuters reports. Pfizer in a letter to health care professionals said that the chemical ethyl methanesulfonate -- or EMS, which is formed during manufacturing -- has been shown to cause cancer and birth defects in animals but that no data from humans are available (Richwine, Reuters, 9/10).
The company advised health care professionals that children who are stable on antiretroviral regimens containing Viracept can remain on the drug, adding that those who need to initiate therapy should not start regimens with Viracept until further notice. The company also said that pregnant women should refrain from starting regimens with Viracept and that those currently receiving it should switch to another drug (AP/Yahoo! News, 9/10). For pregnant women with no alternative treatment options, "FDA and Pfizer agree that the risk-benefit ration remains favorable for the continued use of Viracept," the letter said (Reuters, 9/10).
Pfizer said it is working with FDA to implement immediate and long-term processes to keep EMS levels low (AP/Yahoo! News, 9/10). According to the company, EMS levels are "substantially lower" than those that prompted Roche in June to recall all batches of Viracept in Europe and other countries, Reuters reports. "Pfizer is working with the FDA to prospectively limit EMS levels in Viracept while still considering the immediate needs of patients on therapy," the company said in a statement. Pfizer in the letter said manufacturing changes will reduce EMS levels so the theoretical increased cancer risk for adults over a person's lifetime would be less than one case per 100,000 people exposed (Reuters, 9/10).