Cephalexin vs. Flagyl
See how Cephalexin and Flagyl compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Cephalexin is a cephalosporin antibiotic used for skin, respiratory, bone, and urinary infections caused by susceptible bacteria.
Flagyl (metronidazole) targets anaerobic bacteria and parasites, treating infections like trichomoniasis, amebiasis, and certain anaerobic infections.
The two drugs are rarely interchangeable because they target different types of organisms, though both are older, well-established generics.
Cephalexin vs. Flagyl Drug Summary
Cephalexin
Cephalexin is a first-generation cephalosporin antibacterial used for infections like strep throat, skin infections, and urinary tract infections. It comes as a capsule, tablet, or oral suspension, typically taken two to four times a day. It has been used safely since the early 1970s and is only available as a generic.
Flagyl
Flagyl (metronidazole) is a nitroimidazole antimicrobial used mainly for trichomoniasis, amebiasis, and anaerobic bacterial infections. It comes as an oral tablet, capsule, extended-release tablet, or IV form, usually taken multiple times a day for one to two weeks. Alcohol must be avoided during treatment and for several days afterward.
Cephalexin vs. Flagyl Side Effects
Cephalexin
Flagyl
Cephalexin vs. Flagyl Dosage
Cephalexin
Flagyl
| 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 |
| STAGE | DOSE | WHEN |
| Starting dose | 250 mg three times daily | Days 1-7 |
| Maximum dose | 7.5 mg/kg every 6 hours | Days 1-7 |
| Dose changes | 3 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 |
Flagyl
| STAGE | DOSE | WHEN |
| Starting dose | 250 mg three times daily | Days 1-7 |
| Maximum dose | 7.5 mg/kg every 6 hours | Days 1-7 |
| Dose changes | 3 increases | As tolerated |
Cephalexin vs. Flagyl Indications
Cephalexin
Cephalexin is FDA-approved for a range of bacterial infections caused by susceptible organisms, including respiratory, skin, bone, and urinary tract infections. It is often chosen for outpatient treatment of common bacterial infections in both adults and children.
Respiratory tract infections (strep throat, pneumonia)
Otitis media (middle ear infections)
Skin and skin structure infections
Bone infections
Flagyl
Flagyl is FDA-approved for trichomoniasis, amebiasis, and infections caused by anaerobic bacteria, organisms that thrive without oxygen. It is also commonly prescribed off-label for bacterial vaginosis, though that use follows a different dosing schedule than the FDA-approved indications.
Symptomatic and asymptomatic trichomoniasis
Amebiasis (intestinal parasite infection)
Anaerobic bacterial infections
Bacterial vaginosis (off-label use)
Cephalexin vs. Flagyl Pros and Cons
Cephalexin
Cephalexin has a long safety record and broad use across respiratory, skin, bone, and urinary infections. It does not carry the same alcohol restrictions or carcinogenicity warning that metronidazole does, but it is not effective against anaerobic bacteria or parasites.
Pros
No alcohol interaction or disulfiram-like reaction risk
Available as an oral suspension for children
No boxed warning for carcinogenicity
Broad coverage for common skin, respiratory, and urinary infections
Cons
Not effective against anaerobic bacteria or parasites
Dose adjustment needed for kidney impairment (CrCl below 30 mL/min)
Carries a risk of C. difficile-associated diarrhea
Not effective against trichomoniasis or amebiasis
Flagyl
Flagyl covers infections that cephalexin cannot treat, including anaerobic bacteria and certain parasitic infections. It comes with a boxed carcinogenicity warning and a strict alcohol restriction, along with a risk of neurological side effects with prolonged use.
Pros
Effective against anaerobic bacteria and protozoal infections
Single 2 g dose option available for trichomoniasis
Available in oral, extended-release, and IV forms
Standard treatment for amebiasis and BV
Cons
Boxed warning for carcinogenicity in animal studies
Must avoid alcohol during and for days after treatment
Risk of seizures, peripheral neuropathy, and encephalopathy
Metallic taste is a common complaint during treatment
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