Can a pregnant patient take metronidazole (Flagyl) for bacterial vaginosis (BV)?

From the Guidelines

Yes, metronidazole can be safely used to treat bacterial vaginosis (BV) during pregnancy, specifically in the second trimester, with a recommended regimen of metronidazole 250 mg orally three times a day for 7 days. This recommendation is based on the guidelines for treatment of sexually transmitted diseases published in 1998 by the Centers for Disease Control and Prevention 1. The treatment of BV in high-risk pregnant women, such as those who have previously delivered a premature infant, may reduce preterm delivery.

Key points to consider when treating BV with metronidazole during pregnancy include:

• Screening and treatment should be conducted at the earliest part of the second trimester of pregnancy
• Alternative regimens include metronidazole 2 g orally in a single dose or clindamycin 300 mg orally twice a day for 7 days, as outlined in the 1998 guidelines 1
• Untreated BV has been associated with adverse pregnancy outcomes, including preterm birth, premature rupture of membranes, and postpartum endometritis
• Patients should complete the full course of treatment, even if symptoms resolve earlier, and avoid alcohol during treatment and for 24 hours afterward due to potential disulfiram-like reaction.

From the FDA Drug Label

Pregnancy Teratogenic Effects Pregnancy category B Metronidazole crosses the placental barrier and enters the fetal circulation rapidly. Reproduction studies have been performed in rats at doses up to five times the human dose and have revealed no evidence of impaired fertility or harm to the fetus due to metronidazole No fetotoxicity was observed when metronidazole was administered orally to pregnant mice at 20 mg/kg/day approximately one and a half times the most frequently recommended human dose (750 mg/day) based on mg/kg body weight; however in a single small study where the drug was administered intraperitoneally, some intrauterine deaths were observed The relationship of these findings to the drug is unknown. There are, however, no adequate and well-controlled studies in pregnant women. Because animal reproduction studies are not always predictive of human response, and because metronidazole is a carcinogen in rodents, this drug should be used during pregnancy only if clearly needed Use of metronidazole for trichomoniasis during pregnancy should be restricted to those in whom alternative treatment has been inadequate. Use of metronidazole for trichomoniasis in the first trimester of pregnancy should be carefully evaluated because metronidazole crosses the placental barrier and its effects on the human fetal organogenesis are not known (see above)

Metronidazole use in pregnant patients with BV:

• The FDA drug label indicates that metronidazole is a category B drug, meaning that animal studies have not shown adverse effects, but there are no adequate and well-controlled studies in pregnant women.
• The label advises that metronidazole should be used during pregnancy only if clearly needed.
• For the treatment of trichomoniasis (which is similar to BV), the label recommends restricting use to those in whom alternative treatment has been inadequate.
• The label also advises careful evaluation of use in the first trimester of pregnancy due to the potential risks.
• Key consideration: Metronidazole crosses the placental barrier, and its effects on human fetal organogenesis are not known. Based on the information provided, metronidazole can be used in pregnant patients with BV, but its use should be carefully evaluated and restricted to those in whom alternative treatment has been inadequate, especially in the first trimester of pregnancy 2.

From the Research

Treatment of Bacterial Vaginosis in Pregnancy

• Metronidazole is a commonly used antibiotic for the treatment of bacterial vaginosis (BV) in pregnant women 3, 4, 5.
• Studies have shown that metronidazole can be effective in treating BV in pregnancy, with cure rates ranging from 72% to 87% 3.
• Both oral and vaginal metronidazole can be used to treat BV in pregnancy, with similar efficacy in reducing concentrations of BV-associated anaerobic bacteria 4.

Safety of Metronidazole in Pregnancy

• The safety of metronidazole in pregnancy has been evaluated in several studies, with mixed results 5, 6.
• One study found that metronidazole did not reduce the risk of preterm delivery or other adverse perinatal outcomes in pregnant women with asymptomatic BV 5.
• Another study found that metronidazole was associated with a 70% increased risk of spontaneous abortion, although this risk should be interpreted cautiously due to confounding factors 6.
• The CDC guidelines advocate for the use of metronidazole for the treatment of BV in pregnant women, and it is considered effective in preventing preterm births when used in conjunction with other antibiotics 6.

Alternative Treatment Strategies

• Alternative treatment strategies for BV in pregnancy are being explored, including the use of antimicrobial substances, probiotics, and acidifying agents 7.
• These alternative strategies aim to reestablish the physiologic vaginal environment and improve local immunity response, and may be used in combination with standard therapies to improve treatment efficacy 7.