Metronidazole vs. Cephalexin
See how Metronidazole and Cephalexin compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Metronidazole targets anaerobic bacteria and protozoa, making it a go-to for trichomoniasis, bacterial vaginosis, and abdominal infections, while cephalexin targets staph and strep infections of the skin, respiratory tract, and urinary tract.
Both drugs are inexpensive, decades-old generics, but metronidazole requires avoiding alcohol entirely due to a severe reaction, while cephalexin carries a cross-allergy risk for people with penicillin allergies.
Metronidazole is usually prescribed for short courses of a week or less, while cephalexin's dosing frequency and duration vary more depending on which infection is being treated.
Metronidazole vs. Cephalexin Drug Summary
Metronidazole
Metronidazole is a nitroimidazole antimicrobial used to treat infections caused by anaerobic bacteria and certain protozoa, including trichomoniasis, bacterial vaginosis, and amebiasis. It is usually taken as an oral tablet or capsule two to four times a day, and is also available as an IV, topical, or vaginal formulation.
Cephalexin
Cephalexin is a first-generation cephalosporin antibiotic used to treat bacterial infections of the skin, respiratory tract, ears, bones, and urinary tract. It is taken orally as a capsule, tablet, or liquid suspension, usually every 6 to 12 hours depending on the infection and dose.
Metronidazole vs. Cephalexin Side Effects
Metronidazole
Cephalexin
Metronidazole vs. Cephalexin Dosage
Metronidazole
Cephalexin
| 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 |
| STAGE | DOSE | WHEN |
| Starting dose | 25-50 mg/kg/day divided | At the start |
| Maximum dose | 1 to 4 g/day divided | 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 three times daily | If needed |
| Dose changes | 2 increases | As tolerated |
Cephalexin
| STAGE | DOSE | WHEN |
| Starting dose | 25-50 mg/kg/day divided | At the start |
| Maximum dose | 1 to 4 g/day divided | If needed |
| Dose changes | 4 increases | As tolerated |
Metronidazole vs. Cephalexin Indications
Metronidazole
Metronidazole is FDA-approved for infections caused by anaerobic bacteria and certain protozoa, such as trichomoniasis, bacterial vaginosis, and amebiasis. It also treats intra-abdominal infections like peritonitis and abscesses. Off-label, it is a key part of combination therapy for H. pylori and C. difficile infections.
Trichomoniasis (symptomatic and asymptomatic)
Bacterial vaginosis
Amebiasis
Intra-abdominal infections and abscesses
Off-label: H. pylori and C. difficile treatment
Cephalexin
Cephalexin is FDA-approved for infections of the skin, respiratory tract, ears, bones, and urinary tract caused by susceptible staphylococci and streptococci. It also treats genitourinary infections, including acute prostatitis. Off-label, it is sometimes used as an adjunct for acne or to prevent surgical site infections.
Skin and skin structure infections
Respiratory tract infections
Otitis media
Urinary tract infections, including prostatitis
Bone infections
Metronidazole vs. Cephalexin Pros and Cons
Metronidazole
Metronidazole is a first-line option for trichomoniasis and bacterial vaginosis, with strong activity against anaerobes and protozoa that many other antibiotics lack. It is inexpensive and comes in oral, IV, topical, and vaginal forms, but it carries a boxed warning about carcinogenicity in animal studies and can cause a severe reaction with alcohol.
Pros
First-line treatment for trichomoniasis and bacterial vaginosis
Effective against anaerobic bacteria and protozoa other antibiotics miss
Available in oral, IV, topical, and vaginal forms
Inexpensive, widely available generic
Cons
Must avoid alcohol during and after treatment
Boxed warning for carcinogenicity seen in animal studies
Can cause a persistent metallic taste
Risk of seizures or nerve damage with prolonged use
Cephalexin
Cephalexin is a familiar, well-tolerated choice for common skin, respiratory, ear, and urinary infections caused by susceptible staph and strep bacteria. It has been used safely for decades and does not require avoiding alcohol, but it is not effective against anaerobic bacteria or protozoa, and people with penicillin allergies may react to it too.
Pros
Broad activity against common staph and strep infections
No alcohol restriction during treatment
Long track record of safety since the early 1970s
Available as capsule, tablet, or liquid suspension
Cons
Not effective against anaerobic bacteria or protozoal infections
Cross-reactivity risk for patients with penicillin allergy
Dose must be adjusted for reduced kidney function
Dosing every 6 to 12 hours can be less convenient than shorter courses
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