WEDNESDAY, Aug. 3 (HealthDay News) -- Pregnant women who take ongoing, high doses of the drug fluconazole (brand name Diflucan) may be at increased risk of having babies with birth defects, the U.S. Food and Drug Administration warned Wednesday.

The drug is used to treat yeast infections of the vagina, mouth, throat, esophagus and other organs. It's also used to treat meningitis caused by a certain type of fungus and to prevent yeast infections in patients undergoing chemotherapy or radiation therapy prior to a bone marrow transplant.

The FDA said chronic, high doses (400 to 800 milligrams per day) of fluconazole during the first trimester of pregnancy may increase the risk of a rare and distinct set of birth defects.

There doesn't appear to be any increased risk with a single, low dose (150 mg) to treat vaginal yeast infection.

One expert agreed that the move shouldn't affect most women.

"Diflucan is generally reserved for resistant genital infections and when used for this indication the lower dose regimen is used," said Dr. Edwin R. Guzman, professor in the department of obstetrics and gynecology and director of maternal-fetal medicine at NYU Langone Medical Center, New York City. "It is generally used for non-genital tract/systemic infections and in patients who are immunocompromised. Therefore, long-term high dose use in pregnancy would not be a common occurrence."

He said that if a woman was prescribed the drug during pregnancy, "it would be in unique situations where the benefits would have to be carefully weighed against the fetal risks."

Based on the available information, the FDA has changed the pregnancy category for extended, high-dose fluconazole use (other than vaginal yeast infection) from category C to category D.

Pregnancy category D means there is evidence that this use of the drug poses a risk to human fetuses, but may still be acceptable due to the potential benefits from use in pregnant women with serious or life-threatening conditions, the FDA said.

The pregnancy category for a single, low-dose of fluconazole was not changed and remains category C.

Women who use fluconazole during pregnancy should be informed of the potential risks to the fetus, and women who are or become pregnant while taking the drug should notify their health care providers, the FDA said.

More information

The U.S. Centers for Disease Control and Prevention has more about yeast infections.