Metronidazole

Selected oral labels cover confirmed trichomoniasis, intestinal/liver amebiasis and serious susceptible anaerobic infections, including intra-abdominal, gynecologic, skin, CNS, respiratory, bloodstream, bone/joint and endocardial infections. Mixed infections need aerobic coverage and surgical source control when indicated. Selected IV additionally labels adult colorectal surgical prophylaxis and intra-abdominal infection from birth to under 4 months; other pediatric IV indications are not inferred. Use only for proven or strongly suspected susceptible infection.

Selected vaginal 0.75% gel treats bacterial vaginosis; Nuvessa 1.3% treats BV in females ≥12. Selected dermal 1% gel and 0.75% cream treat inflammatory rosacea lesions. These local products do not establish systemic infection treatment. CDC STI guidance supplies separate oral BV and sex-specific trichomoniasis regimens; oral BV is guideline context rather than an indication explicitly listed in these selected immediate-release oral labels.

CDC recommends oral metronidazole 500 mg twice daily for 7 days for women with trichomoniasis, and 2 g once for men. Vaginal gel is not recommended for trichomoniasis. CDC BV options include oral 500 mg twice daily for 7 days or vaginal 0.75% gel 5 g once daily for 5 days. Persistent/recurrent infection needs reassessment; no unsupervised repeat, resistance or recurrent-BV suppression algorithm is supplied.

Selected immediate-release oral tablets reduce dose 50% in Child-Pugh C; A/B need no adjustment but adverse-effect monitoring. Flagyl 375 supplies specific severe-hepatic schedules: amebiasis 375 mg every 8 hours for 5–10 days; trichomoniasis 375 mg every 24 hours for 7 days. The selected IV label instead requires cautious lower doses and plasma-level/toxicity monitoring in severe hepatic disease, without a numeric formula; do not automatically transplant the oral rule. Oral ESRD requires metabolite-toxicity monitoring; consider clinician-selected supplementation after hemodialysis if dosing cannot be separated. No routine CAPD adjustment in the oral label. Vaginal 0.75% requires caution in severe hepatic disease; no universal local-product adjustment is supplied.

Systemic labels contraindicate metronidazole/nitroimidazole hypersensitivity, Cockayne syndrome, disulfiram within 2 weeks and alcohol/propylene-glycol exposure during treatment and for at least 3 days afterward. Selected oral labels additionally contraindicate first-trimester use specifically for trichomoniasis; this is not a blanket IV or all-indication pregnancy contraindication. Nuvessa contraindicates nitroimidazole/paraben/formulation allergy, disulfiram within 2 weeks and alcohol during/at least 24 hours after. Selected vaginal 0.75% contraindicates nitroimidazole/paraben hypersensitivity. Dermal products contraindicate ingredient hypersensitivity; do not copy every systemic contraindication onto a skin label.

Selected oral and IV labels have a boxed warning that rodent studies showed carcinogenicity and unnecessary use should be avoided; reserve treatment for indicated conditions. This is not proof of human cancer causation. Selected vaginal and dermal labels have no boxed warning, although they discuss systemic animal findings and exposure uncertainties.

Systemic common reactions include GI upset, nausea and metallic taste; severe neurologic, skin, hepatic, blood-count and QT reactions can occur. Dark urine may reflect a metabolite, but new illness still requires assessment. IV can cause thrombophlebitis. Vaginal products can cause yeast infection, irritation, headache or GI symptoms; dermal products burning, dryness or dermatitis. Incidence of voluntary reports is uncertain. Overdose requires emergency/Poison Help assessment and professional supportive care; no specific antidote is known. Swallowed local products or excessive use can produce systemic exposure.

Warfarin/coumarin effects can increase: monitor PT/INR and adjust the anticoagulant as needed. Lithium concentrations/toxicity may increase; check lithium and creatinine several days after starting. Avoid busulfan unless benefit outweighs risk, with specialist concentration/dose review. Cimetidine can reduce clearance; enzyme inducers such as phenytoin/phenobarbital can reduce metronidazole exposure, while phenytoin clearance may also fall. Review QT-prolonging combinations. No universal interaction dose multiplier is supplied.

Follow selected systemic labels: no alcohol or propylene glycol during treatment and for ≥3 days afterward; no disulfiram within 2 weeks. Nuvessa’s alcohol window is ≥24 hours after; selected vaginal 0.75% cautions alcohol during treatment. CDC’s BV guideline concludes convincing evidence for a disulfiram-like alcohol interaction is lacking and abstinence is unnecessary; that guidance differs from these labels. Resolve advice with the pharmacist/prescriber rather than automatically overriding exact-product instructions. Vaginal/dermal labels retain interaction cautions, including anticoagulants, despite lower absorption.

Some NADH-coupled assays for AST, ALT, LDH, triglycerides or glucose may show falsely low/zero results. Tell the laboratory about metronidazole when results are inconsistent; do not diagnose organ or metabolic disease solely from a suspected interference.

Use the product-specific hepatic and dialysis instructions in Dosage. ESRD can accumulate active/other metabolites even when parent-drug single-dose kinetics are unchanged. Older patients may have higher metabolite exposure; monitor tolerance. Oral pediatric evidence is established for amebiasis, not every infection. Selected IV establishes intra-abdominal treatment only from birth to <4 months with listed maturity bands. Nuvessa is labeled at ≥12; selected vaginal 0.75% and dermal products have unestablished pediatric safety/effectiveness.

Metronidazole crosses the placenta; observational evidence is reassuring overall but cannot guarantee safety. Oral selected labels contraindicate first-trimester trichomoniasis treatment, while CDC recommends testing/treating symptomatic pregnant women at any stage. The prescriber must reconcile this difference rather than use a universal first-trimester rule. CDC recommends treating symptomatic BV in pregnancy but advises avoiding 1.3% vaginal gel because data are insufficient. Local labels describe limited pregnancy evidence; verify exact route and indication.

Oral drug appears in milk at levels similar to maternal serum. Selected oral labels allow individualized breastfeeding assessment; pumping/discarding during treatment and for 48 hours after is an alternative, not a mandatory universal interruption. Nuvessa similarly offers a 48-hour option after its last dose. Selected IV and older vaginal/dermal labels discuss choosing between nursing and treatment; low local exposure is not a no-risk guarantee. Obtain a product-, dose- and infant-specific plan.

In susceptible anaerobic organisms, reduction of the nitro group generates reactive intermediates that damage DNA/inhibit synthesis. The precise mechanism is not fully defined. Use susceptibility and infection-site assessment; aerobic coverage may be separately required. Rosacea benefit has an incompletely understood mechanism, with possible anti-inflammatory effects, not a claim that rosacea is a proven metronidazole-sensitive infection.

Oral / IV

Oral absorption is good, peak about 1–2 hours; average healthy-adult half-life about 8 hours. Less than 20% protein-bound.

Elimination

Oxidation and glucuronidation; drug/metabolites mainly recovered in urine. Active metabolite and impairment exposure matter.

Distribution

Systemic drug reaches CSF, abscess fluid, placenta and milk. Neonatal clearance depends on maturity; no adult half-life transplant.

Nuvessa

After one 5 g dose, mean peak about 2% and exposure about 4% of a single oral 500 mg dose; not an oral-dose equivalent.

Dermal gel 1%

Selected face-application study exposure was less than 1% of a single 250 mg oral dose; this does not establish all local products have identical absorption.

Assess infection/site response, culture/susceptibility when appropriate, adherence, neurologic and skin symptoms, hepatic/renal status and interaction risk. Systemic labels recommend WBC checks before/after courses, especially repeat treatment; severe IV hepatic disease may require plasma-level monitoring. Monitor INR or lithium/creatinine when indicated, and IV fluid/sodium tolerance. Local therapy requires irritation and candidiasis assessment. These labels do not establish a universal weekly laboratory schedule.

For trichomoniasis, CDC advises treating current partners and abstaining until treatment is completed and symptoms resolved; women should retest at about 3 months. BV partner management and recurrent-STI algorithms require current condition-specific guidance rather than a blanket rule here. Complete the prescribed course, verify tablet/capsule strength and route, and follow exact alcohol instructions after resolving conflicts. Nuvessa is a one-time bedtime vaginal applicator; follow its IFU and discard after use. Keep dermal products away from eyes and mucosa; report severe rash, numbness, confusion or coordination changes promptly.

Ingredient / route

Metronidazole 250 mg · oral tablet.

Appearance / imprint

White round tablet, I 124.

Example package

American Health Packaging repack; NDC 60687-526-01, 100 unit-dose tablets.

U.S. status

Prescription antibacterial/antiprotozoal; no DEA schedule. Manufacturer/repack and package instructions must be verified.

Selected oral tablets

250 mg (I 124) and 500 mg (I 125). Flagyl capsules 375 mg are a distinct strength/regimen.

Selected IV

500 mg/100 mL = 5 mg/mL ready-to-use single-dose bag; Sun distribution/Gland manufacture.

Vaginal products

0.75% = 7.5 mg/g, 5 g applicator 37.5 mg; Nuvessa 1.3% = 13 mg/g, one 5 g applicator 65 mg.

Selected skin products

Taro gel 1% = 10 mg/g; Fougera cream 0.75% = 7.5 mg/g. A dermal 0.75% product is not a vaginal 0.75% product.

Scope

Other brands, extended-release tablets, compounded oral liquids, dermal lotions and non-U.S. products require their own current labels. No unverified current approval/stock, substitute dose or concentration is inferred.

Selected oral tablets 20–25°C, excursions 15–30°C, protected from light; keep unit-dose blisters intact. Flagyl 375 stores at 15–25°C in a well-closed child-resistant container. Selected IV stores 20–25°C, protected from light/freezing; do not refrigerate, add drugs or use cloudy/leaking bags. Vaginal 0.75% stores 15–30°C, protected from freezing; Nuvessa 20–25°C (15–30°C excursions), no freezing or refrigeration. Selected dermal gel 20–25°C and cream 20–25°C (15–30°C excursions). Verify exact package and secure away from children.