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 |
| Molecular Weight | 171.15 |
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 | Topical metronidazole vaginal gel has minimal systemic absorption; however, animal studies have shown fetal effects at high doses, and there are no adequate well-controlled studies in pregnant women during the first trimester. Use only if clearly needed and benefit outweighs risk. |
| 2nd trimester | Limited human data; systemic absorption is low following vaginal application. No teratogenic effects observed in animal studies at clinically relevant doses. May be used with caution if needed for symptomatic bacterial vaginosis. |
| 3rd trimester | Minimal systemic absorption; no known fetal harm from topical use. Can be used for bacterial vaginosis near term if clinically indicated, as untreated infection may increase risk of preterm labor. |
Clinical note
Comprehensive clinical and safety monograph for METROGEL-VAGINAL (METROGEL-VAGINAL).
| Placental transfer | Metronidazole crosses the placental barrier. Following oral administration, cord blood concentrations approach maternal levels. With vaginal gel, systemic absorption is minimal (1-2% bioavailability), so placental transfer is expected to be low, though not quantified. |
■ FDA Black Box Warning
No FDA boxed warning.
| Serious Effects |
Hypersensitivity to metronidazole or any component of the formulationHypersensitivity to other nitroimidazole derivatives (e.g., tinidazole, secnidazole)
| 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. |
| Food/Dietary | Avoid alcohol and any products containing alcohol (e.g., certain sauces, vinegars, desserts, mouthwashes) during treatment and for at least 48 hours after last dose to prevent disulfiram-like reaction (nausea, vomiting, flushing, headache). No other significant food interactions. |
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| Breastfeeding | Systemic absorption after vaginal application is low (peak plasma concentrations <2% of oral dose). Metronidazole is excreted into breast milk in small amounts; however, the low systemic exposure with vaginal gel suggests minimal risk to the infant. The manufacturer recommends caution due to potential for gastrointestinal disturbance or oral thrush in nursing infants. Consider using with infant monitoring. |
| Lactation Rating | L2 (Limited data - probably compatible) |
| 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. |
| 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. |
| Clinical Pearls | Metronidazole vaginal gel is first-line for bacterial vaginosis. Avoid alcohol during therapy and for 48 hours after last dose due to disulfiram-like reaction. Use caution in patients with Cockayne syndrome due to risk of severe hepatotoxicity. May cause metallic taste. Do not use during menstruation; treatment is typically 5 days but can be extended to 7-10 days for recurrent BV. |
| Patient Advice | Use the applicator to insert the gel into the vagina as directed, usually once or twice daily for 5 days. · Do not drink alcohol or use alcohol-containing products (mouthwash, cough syrup) during treatment and for 2 days after stopping. · You may notice a metallic taste in your mouth, which is common and harmless. · Avoid sexual intercourse or use condoms during treatment to prevent irritation and reinfection. · Wash hands before and after use. Do not use tampons, douches, or other vaginal products during therapy. |