Azithromycin vs. Metronidazole

See how Azithromycin and Metronidazole compare on approved uses, dosing, side effects, and cost.

Key Takeaways

  • Azithromycin is a macrolide antibiotic usually given as a short 3 to 5 day course or single dose, while metronidazole is a nitroimidazole typically taken multiple times a day for about a week.

  • The two drugs treat largely different infections: azithromycin covers respiratory, skin, and some sexually transmitted infections, while metronidazole targets anaerobic bacteria and protozoal infections like trichomoniasis.

  • Metronidazole requires strict alcohol avoidance due to a disulfiram-like reaction, while azithromycin carries its own risks of heart rhythm changes and liver injury.

Azithromycin vs. Metronidazole Drug Summary

Azithromycin

Azithromycin is a macrolide (azalide) antibiotic used for bacterial infections like pneumonia, sinusitis, skin infections, and certain sexually transmitted infections. It is usually taken as tablets or liquid over 1 to 5 days, thanks to its long-lasting tissue levels.

Metronidazole

Metronidazole is a nitroimidazole antimicrobial used for anaerobic bacterial infections and protozoal infections like trichomoniasis and amebiasis. It is typically taken as oral tablets several times a day for about a week, though single-dose and IV options exist.

Azithromycin vs. Metronidazole Side Effects

Azithromycin

Most common
nausea (up to 18%)
vomiting (up to 7%)
diarrhea (up to 14%)
abdominal pain (up to 7%)

Metronidazole

Most common
nausea (reported frequently)
vomiting (occasionally reported)
headache (commonly reported)
anorexia (commonly reported)

Azithromycin vs. Metronidazole Dosage

Azithromycin

Dosage
Dosage Table
STAGE DOSE WHEN
Starting dose 500 mg once Day 1
Maximum dose 5 mg/kg once daily Days 2-5
Dose changes 6 increases As tolerated

Metronidazole

Dosage
Dosage Table
STAGE DOSE WHEN
Starting dose 250 mg three times daily Days 1-7
Maximum dose 500-750 mg three times daily If needed
Dose changes 2 increases As tolerated

Azithromycin vs. Metronidazole Indications

Azithromycin

Azithromycin is FDA-approved for a range of bacterial infections including pneumonia, bronchitis flare-ups, sinusitis, and skin infections. It also treats certain sexually transmitted infections like chlamydia-related urethritis and cervicitis.

  • Community-acquired pneumonia

  • Acute bacterial sinusitis and bronchitis flare-ups

  • Skin and soft tissue infections

  • Urethritis, cervicitis, and pelvic inflammatory disease

  • Acute otitis media (ear infections)

Metronidazole

Metronidazole is FDA-approved for infections caused by anaerobic bacteria and certain parasites, including trichomoniasis, bacterial vaginosis, and amebiasis. It is also used for serious intra-abdominal infections like peritonitis and abscesses.

  • Trichomoniasis (symptomatic and asymptomatic)

  • Bacterial vaginosis

  • Amebiasis and other protozoal infections

  • Intra-abdominal infections and abscesses

  • H. pylori eradication (off-label, combination therapy)

Azithromycin vs. Metronidazole Pros and Cons

Azithromycin

Azithromycin's long tissue half-life allows short 3 to 5 day courses or a single dose, which many patients find easier to complete. It covers a broad range of respiratory and skin pathogens but carries cardiac and liver risks that require caution in some patients.

Pros

  • Short 3 to 5 day courses improve treatment adherence

  • No alcohol restriction during treatment

  • Available as pediatric oral suspension

  • Single-dose options for some infections

Cons

  • Risk of QT interval prolongation and abnormal heart rhythms

  • Rare but serious risk of severe hepatotoxicity

  • Growing bacterial resistance in some regions

  • Not effective against anaerobic or protozoal infections

Metronidazole

Metronidazole remains a first-line choice for trichomoniasis and bacterial vaginosis, with decades of clinical use behind it. Its main drawbacks are a strict need to avoid alcohol and a longer, more frequent dosing schedule than azithromycin.

Pros

  • First-line treatment for trichomoniasis and bacterial vaginosis

  • Effective against anaerobic bacteria and protozoa

  • Available in oral, IV, topical, and vaginal forms

  • Decades of established clinical use

Cons

  • Must strictly avoid alcohol due to disulfiram-like reaction

  • Common metallic taste during treatment

  • Boxed warning for carcinogenicity in animal studies

  • Longer course with multiple daily doses for a week

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