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
Metronidazole
Azithromycin vs. Metronidazole Dosage
Azithromycin
Metronidazole
| 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 |
| 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
| 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
| 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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