Taking high does of the antifungal fluconazole (Diflucan, Pfizer) during the first trimester of pregnancy may cause birth defects, the FDA warns.

The agency has changed the pregnancy category for fluconazole at the 400 mg to 800 mg dose from a category C to a category D.

Category D signifies that there is evidence of fetal risk, but the potential benefits of the drug for serious or life-threatening conditions may make it’s use acceptable in pregnant women despite this risk.

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Case reports from women who were treated with daily doses of fluconazole 400 mg to 800 mg during most or all of the first-trimester of pregnancy indicate potential for the following birth abnormalities: brachycephaly, abnormal facies, abnormal calvarial development, cleft palate, femoral bowing, thin ribs and long bones, arthrogryposis and congenital heart disease.

A single, low 150-mg dose of fluconazole – the dose typically prescribed for patients with vaginal candidiasis – is not associated with birth defects. For this use the pregnancy category remains Category C, according to the CDC.

Fuconazole is also used to treat candidiasis of the mouth, throat, esophagus and other organs, and as prophylaxis to prevent yeast infections in patients undergoing chemotherapy or radiation therapy prior to bone marrow transplant.

The FDA recommends that healthcare professionals counsel pregnant patients or those who become pregnant while taking fluconazole, about potential fetal risks. All women should be told to notify their healthcare professional if they become pregnant while taking fluconazole.

The agency advises clinicians and patients to report any fluconazole-related adverse events to the FDA’s MedWatch Safety Information and Adverse Event Reporting System.