How to Take Metronidazole

Dosing Depends on Your Infection

The correct way to take metronidazole depends entirely on which infection you are treating. The dosing regimens vary significantly by indication, and using the wrong regimen can lead to treatment failure.

For Trichomoniasis (Vaginal Parasite Infection)

Preferred Regimen

Take 2 grams (2000 mg) as a single oral dose – this is the CDC's recommended first-line treatment, achieving 90-95% cure rates 1, 2
Take all tablets at once with food to minimize nausea 3

Alternative Regimen (If Single Dose Fails or Is Not Tolerated)

Take 500 mg by mouth twice daily for 7 days 1, 2
The 7-day regimen may achieve slightly higher cure rates (97% vs 94%) but requires better adherence 4
Recent high-quality evidence from 2018 shows the 7-day regimen is superior, with only 11% treatment failure versus 19% failure with single-dose therapy 5

Critical Alcohol Warning

Avoid ALL alcohol during treatment and for 24 hours after your last dose – this includes mouthwash, cough syrup, and any alcohol-containing products 2, 6
Mixing metronidazole with alcohol causes severe disulfiram-like reactions: flushing, severe nausea, vomiting, and rapid heartbeat 2, 6

For Bacterial Vaginosis (BV)

Preferred Oral Regimen

Take 500 mg by mouth twice daily for 7 days – this achieves approximately 95% cure rates and is the CDC's standard recommendation 2, 6
Take with food to reduce stomach upset 3

Alternative Regimens

Single-Dose Option (Lower Efficacy):

2 grams as a single oral dose achieves only 84% cure rate versus 95% for the 7-day regimen 6
Reserve this only when adherence to 7 days is impossible 6

Vaginal Gel Options (If You Cannot Take Pills):

Metronidazole 0.75% vaginal gel: Insert one full applicator (5 grams) into the vagina once daily at bedtime for 5 days 2, 6
This achieves 70-84% cure rates, slightly lower than oral therapy 6
The gel produces less than 2% of the blood levels of oral metronidazole, causing fewer side effects like nausea and metallic taste 6

Same Alcohol Warning Applies

Avoid all alcohol during treatment and for 24 hours after completion, even with vaginal gel 2, 6

For Intestinal Amebiasis (Parasitic Infection)

Take 750 mg by mouth three times daily for 5-10 days for acute intestinal infection 3
Take 500-750 mg by mouth three times daily for 5-10 days for liver abscess 3

For Anaerobic Bacterial Infections (Serious Infections)

Take 500 mg (7.5 mg/kg) by mouth every 6 hours – this is approximately 500 mg four times daily for a 70 kg adult 3
Maximum dose: Do not exceed 4 grams in 24 hours 3
Duration: Usually 7-10 days, but bone, joint, lung, and heart infections may require longer treatment 3

Common Pitfalls to Avoid

Do NOT Use the Wrong Regimen

Do not use the single 2-gram dose for bacterial vaginosis as first-line therapy – it has an 84% cure rate versus 95% for the 7-day regimen 6
Do not use vaginal gel for trichomoniasis – it does not reach the urethra or glands where the parasite hides and is much less effective than oral therapy 1

Do NOT Drink Alcohol

This is the most common and dangerous mistake patients make 2, 6
The reaction can occur with even small amounts of alcohol 2

Do NOT Stop Early

Complete the entire course even if symptoms resolve 2, 6
Stopping early leads to treatment failure and recurrence 2

Do NOT Assume Your Partner Needs Treatment

For bacterial vaginosis, treating male partners does NOT improve cure rates or prevent recurrence – multiple randomized trials confirm this 6
For trichomoniasis, partners should be treated to prevent reinfection 1, 2

Special Situations

If You Are Pregnant

Metronidazole is contraindicated in the first trimester 2, 6
After the first trimester, the 2-gram single dose can be used for trichomoniasis 1, 2
For bacterial vaginosis in pregnancy, use 250 mg three times daily for 7 days (lower dose to minimize fetal exposure) 6

If You Have Liver Disease

Your doctor should prescribe lower doses because metronidazole accumulates in your blood when your liver is not working properly 3
Close monitoring of blood levels may be necessary 3

If You Are on Dialysis

No dose adjustment is needed because dialysis rapidly removes metronidazole and its breakdown products 3

When to Take With or Without Food

Take with food or milk to reduce nausea and stomach upset 3
Food does not significantly reduce absorption or effectiveness 3

What to Expect

Common Side Effects

Nausea (most common, occurs in ~23% of patients) 5
Metallic taste in mouth 6
Headache (~7% of patients) 5
Vomiting (~4% of patients) 5

When to Call Your Doctor

If symptoms do not improve after completing treatment 2, 6
If you develop severe nausea, vomiting, or cannot keep the medication down 3
If you accidentally consumed alcohol during treatment 2

How should I take metronidazole?

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