Metronidazole (vaginal)

The intravaginal administration of a single 5 gram dose of VANDAZOLE results in relatively lower mean systemic exposure to metronidazole that is approximately 2% to 5% of that achieved following a 500 mg oral dose of metronidazole [see Clinical Pharmacology ( 12.3 )] . The following drug interactions were reported for oral metronidazole. Warfarin and other coumarin anticoagulants: Prolonged anticoagulant effects reported with oral metronidazole; monitor INR and prothrombin time. ( 7.3 ) Lithium: Elevated lithium concentrations reported with oral metronidazole; monitor serum concentrations of lithium. ( 7.4 )

7.1 Disulfiram Use of oral metronidazole has been associated with psychotic reactions in alcoholic patients who are using disulfiram concurrently. VANDAZOLE should not be used by patients who have taken disulfiram within the last two weeks [see Contraindications ( 4.2 )] .

7.2 Alcoholic Beverages Use of oral metronidazole has been associated with a disulfiram-like reaction (abdominal cramps, nausea, vomiting, headaches, and flushing) to alcohol. Alcoholic beverages and preparations containing ethanol or propylene glycol should not be consumed during and for at least three days after VANDAZOLE therapy [see Contraindications ( 4.3 )] .

7.3 Coumarin and Other Oral Anticoagulants Use of oral metronidazole has been reported to potentiate the anticoagulant effect of warfarin and other coumarin anticoagulants, resulting in a prolongation of prothrombin time. This possible drug interaction should be considered when VANDAZOLE is prescribed for patients on this type of anticoagulant therapy. In patients on oral anticoagulants, consider monitoring prothrombin time, international normalized ratio (INR), and other coagulation parameters while on VANDAZOLE.

7.4 Lithium Short-term use of oral metronidazole has been associated with elevation of serum lithium concentrations and, in a few cases signs of lithium toxicity, in patients stabilized on relatively high doses of lithium. Use VANDAZOLE with caution in patients treated with lithium and consider monitoring lithium serum concentrations while on VANDAZOLE.

7.5 Cimetidine Use of oral metronidazole with cimetidine may prolong the half-life and decrease plasma clearance of metronidazole. No dose adjustment of VANDAZOLE is necessary.

8.1 Pregnancy Risk Summary Available data on metronidazole use in pregnant women from published cohort studies, case-control studies, case series, meta analyses, and case reports over several decades have not established a drug-associated risk of major birth defects, miscarriage, or adverse maternal or fetal outcomes. In animal reproduction studies, no adverse developmental effects were demonstrated when oral metronidazole was administered to mice at doses up to six times the recommended human dose (see Data). The estimated background risk of major birth defects and miscarriage for the indicated population is unknown.

All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively. Data Human Data Published case-control studies, cohort studies, meta analyses, case series, and case reports over several decades have not established a risk with metronidazole use in pregnancy and major birth defects, miscarriage, or adverse maternal or fetal outcomes. Many studies included first trimester exposures.

One study showed an increased risk of cleft lip, with or without cleft palate, in infants exposed to metronidazole in-utero; however, these findings were not confirmed. Most studies did not show an increased risk for congenital anomalies or other adverse fetal outcomes following metronidazole exposure during pregnancy. Studies conducted to assess the risk of infant cancer following systemic metronidazole exposure during pregnancy did not show an increased risk; however, the ability of these studies to detect such a signal was limited. Animal Data Animal studies have shown that metronidazole crosses the placental barrier and enters the fetal circulation rapidly.

Oral metronidazole reproductive toxicity studies have been performed in mice at doses up to six times the recommended human dose based on body surface area comparisons and have revealed no evidence of harm to the fetus. However, in a single small study where the drug was administered intraperitoneally, some intrauterine deaths were observed.