METROGEL-VAGINAL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for METROGEL-VAGINAL (METROGEL-VAGINAL).
Metronidazole, a nitroimidazole antimicrobial, undergoes reduction by bacterial nitroreductases to form cytotoxic intermediates that disrupt DNA helical structure, inhibiting nucleic acid synthesis and causing bacterial cell death.
| Metabolism | Hepatic metabolism via oxidation and glucuronidation; major metabolite: hydroxy-metronidazole (active). |
| Excretion | Renal: 60-80% unchanged; fecal/biliary: 6-15% |
| Half-life | Terminal elimination half-life: 6-8 hours (prolonged in hepatic impairment; half-life may exceed 20 hours in severe hepatic disease) |
| Protein binding | <20% bound; primarily to serum albumin (minimal binding) |
| Volume of Distribution | 0.25-0.85 L/kg (widely distributed to tissues, including vaginal mucosa and cerebrospinal fluid) |
| Bioavailability | Intravaginal: Systemic bioavailability approximately 50-60% relative to oral; vaginal absorption variable (mean ~56% of oral dose) |
| Onset of Action | Intravaginal: Symptomatic improvement within 24-72 hours |
| Duration of Action | Duration: Treatment course of 5 days recommended for bacterial vaginosis; clinical effects persist with compliance |
One applicatorful (5 g of 0.75% gel) intravaginally once daily, usually at bedtime, for 5 days.
| Dosage form | GEL |
| Renal impairment | No dose adjustment required for mild to moderate renal impairment. Insufficient data for severe renal impairment (CrCl <30 mL/min); use with caution. |
| Liver impairment | No specific Child-Pugh based adjustments available. Use with caution in severe hepatic impairment due to potential metronidazole accumulation. |
| Pediatric use | Safety and efficacy not established in pediatric patients; data insufficient for weight-based dosing. |
| Geriatric use | No specific dose adjustment required. Use standard dosing with consideration of age-related decline in renal function and potential for concurrent medications. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for METROGEL-VAGINAL (METROGEL-VAGINAL).
| Breastfeeding | Metronidazole is excreted in breast milk; after vaginal administration, systemic absorption is minimal (approximately 2% of oral dose), resulting in low milk concentrations. The M/P ratio is approximately 0.8-1.0 for oral dosing; for vaginal gel, ratio is expected lower. The American Academy of Pediatrics considers single-dose therapy compatible with breastfeeding after timed dosing and discarding milk for 12-24 hours. For chronic use, monitor infant for gastrointestinal disturbances. |
| Teratogenic Risk | Metronidazole vaginal gel (METROGEL-VAGINAL) is classified as FDA Pregnancy Category B. In the first trimester, available data do not show an increased risk of major malformations, but some studies suggest a possible association with cleft lip/palate; use only if clearly needed. In the second and third trimesters, no increased risk of fetal abnormalities has been reported. Avoid use in preterm labor or premature rupture of membranes due to potential systemic absorption. |
■ FDA Black Box Warning
No FDA boxed warning.
| Serious Effects |
["Hypersensitivity to metronidazole or nitroimidazoles","Pregnancy: Contraindicated in first trimester (use only if clearly needed in second/third trimester)","Use with alcohol or propylene glycol","Use with disulfiram (within 2 weeks)"]
| Precautions | ["Carcinogenicity: Avoid unnecessary prolonged use; rodent studies showed tumorigenicity.","Peripheral neuropathy: May occur with high doses or prolonged therapy.","Candidiasis: May overgrow Candida; treat concurrent infections.","Neutropenia: Monitor CBC if retreatment needed.","Alcohol interaction: Disulfiram-like reaction (abdominal cramps, nausea, vomiting) if alcohol consumed within 48 hours.","Hepatic impairment: Use with caution; dose adjustment may be needed."] |
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| Fetal Monitoring | No specific monitoring is routinely required. In patients with hepatic impairment, monitor liver function due to potential metronidazole accumulation. If used in pregnancy, assess for signs of vaginal bleeding or preterm labor. Watch for maternal adverse effects like metallic taste or neuropathy. |
| Fertility Effects | No significant adverse effects on human fertility have been reported. Metronidazole does not impair spermatogenesis or oogenesis in animal studies. |