Antibiotic (Nitroimidazole) — BV Treatment Pregnancy: Caution in first trimester — second/third trimester use accepted; treat symptomatic BV

Metronidazole (Bacterial Vaginosis)

Brand names: Flagyl, Zidoval (vaginal gel)

Adult dose

Dose: Standard oral: 400 mg BD for 5–7 days. Alternative stat dose: 2 g oral single dose. Vaginal gel (Zidoval 0.75%): one applicator (5 g) vaginally at night for 5 nights

Route: Oral or vaginal

Frequency: BD (oral) or once nightly (vaginal)

Max: 2 g single dose; 400 mg BD × 7 days oral course

BASHH 2021 guidelines: 400 mg BD × 5–7 days preferred (higher cure rate than 2 g stat). Vaginal gel: equivalent efficacy to oral, with lower GI side effects. Avoid alcohol during treatment and for 48h after. BV in pregnancy: treat with 400 mg BD × 5–7 days — 2 g stat dose has lower cure rate in pregnancy.

Paediatric dose

Route: N/A

Frequency: N/A

Max: N/A

Not applicable in obstetric/gynaecological BV indication

Dose adjustments

Renal

No dose adjustment required for standard courses

Hepatic

Reduce dose or extend intervals in severe hepatic impairment

Clinical pearls

BV is the commonest vaginal infection in reproductive-age women — Gardnerella vaginalis overgrowth
Diagnosis: Amsel criteria (3 of 4: homogenous grey discharge, pH >4.5, clue cells on microscopy, positive whiff test)
7-day course outperforms 2 g stat dose for BV — BASHH 2021 recommends BD × 5–7 days as first line
Recurrent BV: consider vaginal pH management (Balance Activ), boric acid, or metronidazole vaginal gel twice weekly for 6 months
Pregnancy: BV associated with preterm birth — treat if symptomatic; 400 mg BD orally preferred over 2 g stat in pregnancy

Contraindications

First trimester of pregnancy (relative — use with caution; 400 mg BD preferred if treatment needed)
Hypersensitivity to nitroimidazoles
Disulfiram use

Side effects

Metallic taste (common)
Nausea and GI upset
Disulfiram-like reaction with alcohol
Peripheral neuropathy (prolonged courses)
Vulvovaginal irritation (vaginal gel)

Interactions

Alcohol — disulfiram-like reaction (severe)
Warfarin — significantly potentiates INR
Disulfiram — psychotic reactions (contraindicated)

Monitoring

Symptom resolution at 1 month
Recurrence assessment
Alcohol counselling

Reference: BNFc; BASHH BV Guideline 2021; NICE CKS Bacterial Vaginosis; BNF. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways