Metronidazole dosage: practical dosing for common infections

Metronidazole treats anaerobic bacteria and certain parasites. Getting the dose right matters: too little may not clear the infection, too long can cause nerve damage. Below are common, practical dosing examples for adults and brief notes for kids. Always follow your prescriber's directions — these are typical ranges used in clinics.

Common dosing by infection

Here are typical adult regimens you’ll hear from doctors. These are common starting points, not a one-size-fits-all order.

  • Trichomoniasis: Either a single 2 g oral dose once, or 500 mg twice daily for 7 days. Many clinicians prefer the 7-day course for better cure rates in some cases.
  • Bacterial vaginosis: 500 mg orally twice a day for 7 days is standard. A single 2 g dose may be used but often works less well.
  • Giardiasis: 250 mg three times daily for 5 days is common. Some use 400–500 mg twice daily for 5 days.
  • Anaerobic infections (intra-abdominal, pelvic): 500 mg IV every 8 hours or 500 mg orally every 8 hours. Duration depends on source control and severity — often 5–14 days.
  • C. difficile: Current guidelines favor oral vancomycin or fidaxomicin first. Metronidazole is rarely first choice now and is only used if other options are unavailable.

Pediatric notes: Doctors usually dose by weight (for example, 15 mg/kg/day divided into three doses for some infections). Kids need a specific prescription — don’t estimate at home.

Safety, interactions, and red flags

Avoid alcohol during treatment and for 48 hours after the last dose — mixing can cause flushing, nausea, and worse symptoms. Metronidazole can raise the effect of blood thinners like warfarin, so your doctor may check your INR if you’re on anticoagulants.

Common side effects are nausea, metallic taste, and stomach upset. Using metronidazole for more than 10–14 days increases the risk of peripheral neuropathy (tingling or numbness). Stop and call your provider if you develop numbness, severe headaches, seizures, or severe allergic reactions.

If you have liver disease, dose changes or extra monitoring may be needed because the drug is processed by the liver. Kidney disease usually doesn’t require major changes. Pregnant or breastfeeding? Talk with your clinician — metronidazole is used in pregnancy for certain infections, but choices depend on the situation.

Don’t share antibiotics or use leftover pills. If symptoms don’t improve in 48–72 hours, worsen, or return after finishing treatment, contact your healthcare provider — you may need a different drug or tests to confirm the cause.

Short, practical takeaway: follow the exact dose and length your prescriber gives, avoid alcohol, watch for numbness or severe side effects, and reach out to your clinic if things aren’t improving. That keeps treatment safe and effective.