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

Most common
Vomiting (rate not quantified in current label)
Nausea (rate not quantified in current label)
Diarrhea (rate not quantified in current label)
Dyspepsia (rate not quantified in current label)

Trimethoprim

Most common
Vomiting (common, rate not specified in label)
Nausea (common, rate not specified in label)
Rash (2.9% to 6.7%)
Pruritus (common, rate not specified in label)

Keflex vs. Trimethoprim Dosage

Keflex

Dosage
Dosage Table
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

Dosage
Dosage Table
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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