Viracept caution issued by Pfizer

WASHINGTON, Sept. 10 (UPI) -- Pfizer Inc. issued a "Dear Healhcare Professional" letter Monday warning of the presence of an impurity in its Viracept medication.

Pfizer said it had discovered ethyl methanesulfonate, or EMS, had been introduced during the production process into Viracept (nelfinavir), which is indicated to help control human immunodeficiency virus infection.

The U.S. Food and Drug Administration said EMS is a potential human carcinogen. Data from animal studies indicate EMS is teratogenic, mutagenic and carcinogenic -- however, no data from humans exist.

The FDA said it asked Pfizer to implement new specifications to limit the presence of EMS in Pfizer-manufactured Viracept products marked in the United States.

However, the FDA and Pfizer agreed the benefit-risk ratio remains favorable for the continued use of Viracept. But pediatric patients and pregnant women who need to begin HIV or antiretroviral treatment should not start regimens containing Viracept until further notice, the FDA said.