Second, on September 10, 2007, Pfizer, Inc. issued a letter*
warning health-care providers about the use of Viracept® (nelfinavir)
(Pfizer, Inc., New York, New York), another protease inhibitor, because the Viracept manufactured in Europe contained high levels of ethyl methane mesylate (EMS). EMS is a byproduct of the manufacturing process and a known animal carcinogen, mutagen, and teratogen. The level at which EMS might become carcinogenic or teratogenic in humans is not known. The warning in the letter applies to pregnant women and states that information about the ability of EMS to cross the placenta or to enter breast milk is currently unknown. A review of data from the Antiretroviral Pregnancy Registry, which collects data on approximately 6,000 HIV-infected pregnant women, indicated that, during January 1989–January 2007, no statistically significant difference was observed in the prevalence of birth defects among the infants of women who used Viracept compared with those whose mothers used other antiretroviral therapies.3 Nonetheless, the Food and Drug Administration (FDA) recommends that pregnant women limit their exposure to EMS during pregnancy. Until further notice, pregnant women who need to begin antiretroviral therapy or HIV PEP should not be offered regimens containing Viracept. As a precautionary measure,
pregnant women currently receiving Viracept should be switched to an alternative antiretroviral therapy while Pfizer and FDA work to implement a long-term EMS specification for Viracept. Specific recommendations for use of antiretroviral agents in pregnant HIV-1–infected patients are indicated in the U.S. Department of Health and Human Services guidelines4 and can be consulted to determine an alternative treatment option.