U.S. officials and the drugmaker Pfizer Inc reported that a potential human carcinogen has been found in batches of Viracept, AIDS drug manufactured by this company.

Viracept, generically known as nelfinavir, belongs to a class of AIDS drugs called protease inhibitors. It is often used in many drug cocktails for HIV virus suppression.

Tests conducted found that a potential human carcinogen ethyl methanesulfonate, or EMS is being formed during manufacturing of the drug. EMS has been found to cause cancer and birth defects in animals, but no such data exists for humans.

EMS levels detected in Viracept productions were much lower to those found in the Roche’s HIV suppressant drug that has been recalled from production.

Pfizer and the FDA are working together to limit EMS levels in Viracept, while still considering the immediate needs of patients on therapy.
The manufacturer reported that they will make changes in production process that will lead to reduction of EMS levels. These changes will make this theoretical increased cancer risk for adults over a lifetime be less than 1 case per 100,000 people exposed.

Pediatric patients who are stable on Viracept will continue to be treated with the drug while the pregnant women will be switched to an alternative medicine until the manufacturing changes are made. Those pregnant women with no alternative treatment options will continue to use Viracept as the risk-benefit ratio remains favorable for the use of the drug, FDA and Pfizer agree had agreed.

These findings made Pfizer shares fall 1.2 % to close at $23.96 on the New York Stock Exchange.