Keflex vs. Trimethoprim
See how Keflex and Trimethoprim compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Keflex treats a broad range of bacterial infections, while trimethoprim is FDA-approved only for uncomplicated urinary tract infections.
Both are oral antibiotics, but Keflex dosing varies by infection type and severity, while trimethoprim follows a standard 10-day UTI regimen.
Trimethoprim's key risks are hyperkalemia and blood cell disorders, while Keflex's main risks are C. diff diarrhea and seizures with kidney impairment.
Keflex vs. Trimethoprim Drug Summary
Keflex
Keflex (cephalexin) is a first-generation cephalosporin antibiotic used for bacterial infections, including certain urinary tract infections. It is taken as an oral capsule, tablet, or liquid, typically several times a day for one to two weeks depending on the infection.
Trimethoprim
Trimethoprim is a urinary anti-infective that blocks bacterial folate production, and it is FDA-approved specifically for treating uncomplicated urinary tract infections caused by susceptible bacteria. It comes as an oral tablet taken once or twice daily for a 10-day course.
Keflex vs. Trimethoprim Side Effects
Keflex
Trimethoprim
Keflex vs. Trimethoprim Dosage
Keflex
Trimethoprim
| STAGE | DOSE | WHEN |
| Starting dose | 25-50 mg/kg/day divided | At the start |
| Maximum dose | up to 4 g/day divided | If needed |
| Dose changes | 3 increases | As tolerated |
| STAGE | DOSE | WHEN |
| Starting dose | 100 mg every 12 hours | Days 1-10 |
| Maximum dose | 200 mg once daily | Days 1-10 |
| Dose changes | 1 increase | As tolerated |
Keflex
| STAGE | DOSE | WHEN |
| Starting dose | 25-50 mg/kg/day divided | At the start |
| Maximum dose | up to 4 g/day divided | If needed |
| Dose changes | 3 increases | As tolerated |
Trimethoprim
| STAGE | DOSE | WHEN |
| Starting dose | 100 mg every 12 hours | Days 1-10 |
| Maximum dose | 200 mg once daily | Days 1-10 |
| Dose changes | 1 increase | As tolerated |
Keflex vs. Trimethoprim Indications
Keflex
Keflex is FDA-approved for a wide range of bacterial infections, including genitourinary tract infections, respiratory infections, skin infections, and bone infections. It is also sometimes used off-label to help prevent infection after surgery.
Genitourinary tract infections (including UTIs)
Respiratory tract infections
Otitis media
Trimethoprim
Trimethoprim is FDA-approved specifically for acute, uncomplicated urinary tract infections caused by susceptible bacteria like E. coli and Klebsiella. It is also used off-label to prevent recurrent UTIs and, combined with dapsone, to prevent Pneumocystis pneumonia.
Acute uncomplicated urinary tract infections
Recurrent UTI prevention (off-label)
Pneumocystis pneumonia prophylaxis with dapsone (off-label)
Keflex vs. Trimethoprim Pros and Cons
Keflex
Keflex is a well-established antibiotic with decades of clinical use across many infection types, including urinary tract infections. It is widely covered by insurance as a generic, though dosing frequency can be higher than some newer options.
Pros
FDA-approved for multiple infection types beyond UTIs, including skin and respiratory infections
Available as capsule, tablet, or oral liquid for flexible dosing
Long, well-established track record dating back to 1971
Cons
Some regimens require dosing every 6 hours
Carries risk of C. difficile-associated diarrhea
Can raise metformin levels, requiring blood sugar monitoring
Seizure risk if it accumulates in patients with kidney impairment
Trimethoprim
Trimethoprim offers a simple, short course designed specifically for uncomplicated UTIs, with once- or twice-daily dosing. It is generally well covered by insurance as a generic, though its narrower spectrum limits it to specific bacteria.
Pros
Specifically approved for uncomplicated UTIs with a defined 10-day course
Simple once- or twice-daily dosing
Lacks the sulfonamide component, an alternative for sulfa-sensitive patients
Cons
Narrower spectrum, approved only for specific UTI-causing bacteria
Risk of hyperkalemia, even without typical risk factors
Can cause blood disorders like megaloblastic anemia and thrombocytopenia
Risk of severe skin reactions including Stevens-Johnson syndrome
Common Symptoms and Related Diseases You Can Explore
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