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Probe · metronidazole · 3 min read

How much metronidazole does a US Flagyl order write?

A US Flagyl order writes 250 mg or 500 mg oral tablets. This vault follows 250 mg. Peak plasma in the classic set sat near 6 mcg/mL after 250 mg and near 12 mcg/mL after 500 mg. Trichomoniasis can use 250 mg three times daily for seven days, or 2 g in one day. Serious anaerobic oral dosing is about 500 mg every six hours in a 70 kg adult (7.5 mg/kg). Do not let the window 'upgrade' 250 mg to 500 mg without a rewrite. See the 250 mg vault.

Medically reviewed by Dr. Mateo Ruiz, MD - Clinical pharmacology, Barcelona

Last reviewed

Updated

01How the milligram changes the peak

Forest-green still life: small white tablet beside a larger twin

Plasma concentrations are proportional to the dose. 250 mg, 500 mg, and 2,000 mg oral doses produced peaks near 6, 12, and 40 mcg/mL. Taste intensity does not map one-to-one to those numbers.

The alcohol hold does not shrink when the stamp is 500 mg. Count three days from the last swallow on either tablet.

02Where 250 mg three times daily is the labelled row

Seven-day trichomoniasis treatment on Flagyl is 250 mg three times daily for seven consecutive days. That is a 250 mg job. The one-day alternative is 2 g, not a 500 mg 'shortcut' you invent.

Comparative notes on the insert suggest seven-day smear and symptom cure may beat one-day treatment. The writer picks the row. Details on seven days versus a 2 g day.

03Why this site keeps saying 250 mg

The vault and these probes describe the 250 mg tablet because that is the strength on the title line. 500 mg still exists as the other oral Flagyl tablet. Bring the milligram that was written.

Ask the pharmacist to dispense the strength on the paper. A 500 mg course is a different count and a different set of directions.

04Which oral strengths Flagyl lists

HOW SUPPLIED names 250 mg round blue film-coated tablets and 500 mg oblong blue film-coated tablets. Both contain metronidazole. Both are prescription tablets.

The 250 mg brand tablet is debossed SEARLE 1831 / FLAGYL 250. The 500 mg brand tablet is debossed FLAGYL on one side and 500 on the other. Generics use other marks.

05Where 500 mg shows up in adult anaerobic math

Usual adult oral dosing for most serious anaerobic infections is 7.5 mg/kg every six hours, about 500 mg for a 70 kg adult, with a 4 g ceiling in 24 hours. IV metronidazole usually starts that work.

A 250 mg tablet can only meet that math if the directions say how many tablets per dose. Do not assume one 250 mg swallow equals the 70 kg row.

06What the clerk cannot rewrite

If the script says 250 mg three times daily, a 500 mg twice-daily hand-off needs the prescriber. Same daily milligrams are possible only when someone writes them. The window does not 'simplify' Flagyl.

Amebiasis rows use 500 mg or 750 mg three times daily, not a silent swap from a 250 mg trichomoniasis pack. Name the infection on the indication probe.

Sources

  1. Pfizer FLAGYL (metronidazole) tablets prescribing information, LAB-0162-20.0, revised July 2024.
  2. DailyMed metronidazole / Flagyl oral tablet labels (250 mg and 500 mg).

Checked against the current label and reviewed by Dr. Mateo Ruiz. See Probe, Assay, Glow-check, Seal.

Vault consult

Answers follow the U.S. Flagyl label.

Nil X. My script says Flagyl. Which milligram should I get?

Vault reply

The paper should say 250 mg or 500 mg. This vault follows 250 mg. Ask the writer if the slip is blank.

Olga J. Can I take one 500 mg tablet instead of two 250 mg?

Vault reply

Only if the directions were written that way. Do not invent the swap. Peaks scale with the milligram you actually swallow.

Pere Y. Is 500 mg a better Flagyl for the same infection?

Vault reply

It is a different tablet. Trichomoniasis seven-day Flagyl is 250 mg three times daily. Anaerobic adult math often lands near 500 mg every six hours.

Before you start, stop, or change any medicine, speak with your prescriber or pharmacist - they hold your chart, this vault card does not. Open the vault disclaimer.