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Ask · metronidazole

How much metronidazole does the US label write?

4 min read · Reviewed

Medically reviewed by Dr. Priya Natarajan, MD - Clinical pharmacology, Dublin

Five hundred milligrams is the tablet this shelf locks. US Flagyl tablets also come as 250 mg. Trichomoniasis is 2 g once, or 250 mg three times daily for seven days. Bacterial vaginosis is often written as 500 mg twice daily for seven days. Amebiasis writes 500 or 750 mg three times daily for 5 to 10 days. Follow the indication on the order.

01What if Child-Pugh C is already on the chart?

Cut the FLAGYL dose by 50% in severe hepatic impairment (Child-Pugh C). That group showed a 114% higher 24-hour AUC after 500 mg IV. Mild or moderate impairment raised AUC by about 54% and 53% and does not get an automatic cut; those patients are monitored for metronidazole reactions. People over 70 had a 40% to 80% higher hydroxy-metabolite AUC after 500 mg, with no clear rise in parent AUC. See the metronidazole shelf.

02How much metronidazole is a trichomoniasis order?

The US tablet PI writes two adult options. One-day treatment is 2 g, as a single dose or as 1 g twice that same day. The seven-day course is 250 mg three times daily for seven consecutive days. Follow the current US PI for the indication actually on the order. Male treatment is individualized the same way.

Pregnant patients are not treated in the first trimester. If treatment is later required and alternatives failed, the one-day course is not used, because it drives higher serum levels into fetal circulation. Repeat courses, when needed, wait four to six weeks and reconfirm the organism.

03How much for amebiasis?

Acute intestinal amebiasis in adults is 750 mg orally three times daily for 5 to 10 days. Amebic liver abscess is 500 mg or 750 mg three times daily for 5 to 10 days. Drainage of pus can still be needed with the tablets. Bactericidal concentrations of metronidazole have been found in pus from hepatic abscesses.

Pediatric amebiasis is the one pediatric use the US tablet label has established: 35 to 50 mg/kg per 24 hours, split into three oral doses, for 10 days. Safety and effectiveness in children have not been established for the other labelled infections.

04How much for a serious anaerobic infection?

Most serious anaerobic infections start with intravenous metronidazole. The usual adult oral step is 7.5 mg/kg every six hours, about 500 mg for a 70 kg adult. Do not exceed 4 g in 24 hours. Surgery still belongs with the tablets when the infection needs drainage.

Usual duration is 7 to 10 days. Bone, joint, lower respiratory tract, and endocardium infections may run longer. The milligram is weight-based until the writer rounds it to a 500 mg tablet. In a mixed infection, a second drug covers the aerobes.

05How much is written when the order says bacterial vaginosis?

A common written course is 500 mg twice daily for seven days. Name that indication on the order. No cure percentage is attached to that line here. The 500 mg tablet this shelf locks is the piece that course counts twice a day.

Seven days here is a swallow calendar. It is not the eight-hour half-life. Do not borrow a 2 g trichomoniasis day for this indication because a search page mixed them. The calendar question is on how long a Flagyl course is.

06What tablet strengths does the US label supply?

Two oral strengths sit on the US supply line: 250 mg and 500 mg. Brand 500 mg tablets are oblong, blue, and film coated, with FLAGYL on one side and 500 on the other. This site talks about 500. The fill is still the strength on the written line.

A 2 g day is four 500 mg tablets, or the counted 250 mg pieces the order named. Peak work at those oral doses was about 6, 12, and 40 mcg/mL. How you obtain that line sits on how to get metronidazole.

Before you start, stop, or change any medicine, speak with your prescriber or pharmacist. They hold your chart. This bin card does not. Open the bin disclaimer.

Sources

  1. US Flagyl (metronidazole) tablets PI, Pfizer LAB-0162-20.0, revised 07/2024; Dosage and Administration; How Supplied.
  2. CDC STI Treatment Guidelines 2021: metronidazole 500 mg twice daily for 7 days is a recommended BV regimen.

Checked against the current label and reviewed by Dr. Priya Natarajan. See Pick → Check → Tag → Bin.

Bin thread

Answers follow the U.S. Flagyl label.

Tor asks

Is 500 mg twice daily the trichomoniasis line on the tablet PI?

The US Flagyl tablet PI writes 2 g once, or 250 mg three times daily for seven days. Follow the indication and the current PI on the order in front of you. 500 mg twice daily for seven days is a common written bacterial vaginosis course when that indication is named.

Pavel asks

Can I split a 500 mg tablet to make 250 mg?

Only if the writer and the pharmacist set that up. This shelf talks about 500 mg as the tablet, not as a home split. Brand 500 mg is film coated. The seven-day trichomoniasis line on the tablet PI is 250 mg three times daily.

Reed asks

Does 750 mg three times daily use the 500 mg tablet?

750 mg is an amebiasis milligram - intestinal disease at 750 mg three times daily for 5 to 10 days. The pharmacy counts tablets to that total. There is no 750 mg Flagyl tablet on this shelf.