Metronidazole vs. Keflex
See how Metronidazole and Keflex compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Metronidazole targets parasites, anaerobic bacteria, and vaginal infections, while Keflex treats skin, respiratory, bone, and urinary infections from susceptible bacteria.
Metronidazole carries a boxed warning about carcinogenicity in animal studies and requires strict alcohol avoidance, while Keflex's main risks are allergic reactions and C. diff-associated diarrhea.
Both are affordable generics, but metronidazole is typically the less expensive option per course of treatment.
Metronidazole vs. Keflex Drug Summary
Metronidazole
Metronidazole is a nitroimidazole antimicrobial used for trichomoniasis, bacterial vaginosis, amebiasis, and infections caused by anaerobic bacteria. It's usually taken as an oral tablet or capsule several times a day for about a week, and it also comes in IV, topical gel, and vaginal gel forms. It has been used since 1963 and remains a first-line treatment for several parasitic and anaerobic infections.
Keflex
Keflex (cephalexin) is a first-generation cephalosporin antibiotic used for respiratory, skin, bone, and urinary tract infections caused by susceptible bacteria. It's taken orally as a capsule, tablet, or liquid, usually every 6 to 12 hours for 7 to 14 days. Approved in 1971, it remains one of the most widely prescribed oral cephalosporins.
Metronidazole vs. Keflex Side Effects
Metronidazole
Keflex
Metronidazole vs. Keflex Dosage
Metronidazole
Keflex
| STAGE | DOSE | WHEN |
| Starting dose | 250 mg three times daily | Days 1-7 |
| Maximum dose | 2 g single or divided dose | Day 1 |
| Dose changes | 1 increase | As tolerated |
| STAGE | DOSE | WHEN |
| Starting dose | 25-50 mg/kg/day divided | At the start |
| Maximum dose | 25-50 mg/kg/day divided | Same as starting |
| Dose changes | None | Fixed dose |
Metronidazole
| STAGE | DOSE | WHEN |
| Starting dose | 250 mg three times daily | Days 1-7 |
| Maximum dose | 2 g single or divided dose | Day 1 |
| Dose changes | 1 increase | As tolerated |
Keflex
| STAGE | DOSE | WHEN |
| Starting dose | 25-50 mg/kg/day divided | At the start |
| Maximum dose | 25-50 mg/kg/day divided | Same as starting |
| Dose changes | None | Fixed dose |
Metronidazole vs. Keflex Indications
Metronidazole
Metronidazole is FDA-approved for trichomoniasis, bacterial vaginosis, amebiasis, and serious anaerobic bacterial infections such as intra-abdominal infections. It's also used off-label for H. pylori eradication and C. difficile infections. It is not effective against viral infections like the common cold.
Trichomoniasis (symptomatic and asymptomatic)
Bacterial vaginosis
Amebiasis
Intra-abdominal infections (peritonitis, abscess)
Anaerobic bacterial infections
Keflex
Keflex is FDA-approved for respiratory tract infections, otitis media, skin and skin structure infections, bone infections, and genitourinary tract infections caused by susceptible bacteria. It's sometimes used off-label to help prevent surgical site infections. It is not effective against Pseudomonas or Acinetobacter species.
Respiratory tract infections
Otitis media
Skin and skin structure infections
Bone infections
Genitourinary tract infections
Metronidazole vs. Keflex Pros and Cons
Metronidazole
Metronidazole works well against parasites and anaerobic bacteria and comes in several forms for different infection sites. Its long history of use has produced a well-documented safety profile, though it carries a boxed warning about carcinogenicity seen in animal studies and requires strict alcohol avoidance.
Pros
First-line option for trichomoniasis and bacterial vaginosis
Available in oral, IV, topical, and vaginal forms
Long track record of use dating back to 1963
Roughly $15 to $40 per month, less expensive than Keflex
Cons
Boxed warning for carcinogenicity shown in animal studies
Cannot be combined with alcohol due to severe reaction risk
Contraindicated with disulfiram and in Cockayne syndrome
Risk of neurological effects like seizures and neuropathy
Keflex
Keflex covers many common bacterial infections affecting the skin, bones, and respiratory tract with a well-established safety record. It does not carry metronidazole's alcohol restriction or carcinogenicity warning, but it is not active against certain resistant bacteria like Pseudomonas.
Pros
Effective against a broad range of skin, bone, and respiratory infections
No restriction on alcohol use during treatment
Widely prescribed with a long safety record since 1971
Available as capsule, tablet, or liquid for flexible dosing
Cons
Not effective against Pseudomonas or Acinetobacter infections
Contraindicated in patients allergic to cephalosporins
Can raise metformin levels, increasing hypoglycemia risk
Roughly $53 to $95 per short course, pricier than metronidazole
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