Amoxicillin vs. Metronidazole
See how Amoxicillin and Metronidazole compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Amoxicillin is a penicillin-class antibiotic used for ear, throat, respiratory, skin, and urinary infections, while metronidazole targets anaerobic bacteria and parasites like trichomoniasis and bacterial vaginosis.
Both are inexpensive generic antibiotics, but metronidazole carries a boxed warning for carcinogenicity in animal studies and cannot be combined with alcohol.
Amoxicillin is usually dosed two to three times daily for days to weeks, while metronidazole's schedule ranges from a single dose to a week-long three-times-daily course depending on the infection.
Amoxicillin vs. Metronidazole Drug Summary
Amoxicillin
Amoxicillin is an aminopenicillin antibiotic that treats bacterial infections of the ear, throat, sinuses, lungs, skin, and urinary tract. It also treats gonorrhea and, in combination regimens, H. pylori infection. It's taken orally as a capsule, tablet, chewable tablet, or liquid suspension, usually two to three times a day.
Metronidazole
Metronidazole is a nitroimidazole antimicrobial that treats parasitic and anaerobic bacterial infections, including trichomoniasis, bacterial vaginosis, amebiasis, and intra-abdominal infections. It's also used off-label for H. pylori and C. difficile. It comes as an oral tablet or capsule, with dosing that ranges from a single dose to a week of three-times-daily treatment.
Amoxicillin vs. Metronidazole Side Effects
Amoxicillin
Metronidazole
Amoxicillin vs. Metronidazole Dosage
Amoxicillin
Metronidazole
| STAGE | DOSE | WHEN |
| Starting dose | 250 mg every 8 hours | At the start |
| Maximum dose | 1 g three times daily | If needed |
| Dose changes | 4 increases | As tolerated |
| STAGE | DOSE | WHEN |
| Starting dose | 250 mg three times daily | Days 1-7 |
| Maximum dose | 500-750 mg, 3x daily | If needed |
| Dose changes | 2 increases | As tolerated |
Amoxicillin
| STAGE | DOSE | WHEN |
| Starting dose | 250 mg every 8 hours | At the start |
| Maximum dose | 1 g three times daily | If needed |
| Dose changes | 4 increases | As tolerated |
Metronidazole
| STAGE | DOSE | WHEN |
| Starting dose | 250 mg three times daily | Days 1-7 |
| Maximum dose | 500-750 mg, 3x daily | If needed |
| Dose changes | 2 increases | As tolerated |
Amoxicillin vs. Metronidazole Indications
Amoxicillin
Amoxicillin is FDA-approved for common bacterial infections affecting the ears, nose, throat, lungs, skin, and urinary tract. It's also approved for uncomplicated gonorrhea and, combined with other drugs, for eradicating H. pylori. It is not effective against viral infections.
Ear, nose, and throat infections
Lower respiratory tract infections
Skin and skin structure infections
Urinary tract infections
H. pylori eradication (combination therapy)
Metronidazole
Metronidazole is FDA-approved for trichomoniasis, bacterial vaginosis, amebiasis, and anaerobic bacterial infections, including intra-abdominal infections. It's also commonly used off-label for H. pylori and C. difficile infections. It is not effective against viral infections.
Trichomoniasis
Bacterial vaginosis
Amebiasis
Intra-abdominal infections (peritonitis, abscess)
H. pylori and C. difficile (off-label)
Amoxicillin vs. Metronidazole Pros and Cons
Amoxicillin
Amoxicillin has a long safety record and is one of the most affordable, widely prescribed antibiotics available. It works well for common respiratory, ear, and urinary infections but carries a risk of allergic reactions, including rare anaphylaxis.
Pros
Available as chewable tablets and liquid for children
Low cost, widely available generic
Fewer serious boxed warnings than metronidazole
Effective for common ear, sinus, and respiratory infections
Cons
Risk of allergic reaction, including anaphylaxis
Not effective against anaerobic bacteria or parasites
Can cause severe rash in patients with mononucleosis
Bacterial resistance is increasingly common
Metronidazole
Metronidazole is a first-line treatment for trichomoniasis and bacterial vaginosis and covers infections amoxicillin cannot treat, such as anaerobic bacteria and parasites. It carries a boxed warning for carcinogenicity in animal studies and cannot be combined with alcohol.
Pros
First-line therapy for trichomoniasis and bacterial vaginosis
Covers anaerobic bacteria and certain parasites
Available in oral, IV, topical, and vaginal forms
Useful off-label for C. difficile and H. pylori
Cons
Boxed warning for carcinogenicity in animal studies
Causes disulfiram-like reaction with alcohol
Risk of seizures, neuropathy, and metallic taste
Contraindicated with disulfiram and Cockayne syndrome
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