Fosfomycin vs. Keflex
See how Fosfomycin and Keflex compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Fosfomycin treats uncomplicated UTI with a single oral dose, while Keflex requires multiple doses a day for 7 to 14 days.
Fosfomycin is FDA-approved only for uncomplicated cystitis in women, while Keflex covers many infection types beyond UTI.
Keflex carries added warnings around C. difficile diarrhea and seizure risk with kidney impairment that fosfomycin does not share.
Fosfomycin vs. Keflex Drug Summary
Fosfomycin
Fosfomycin is a phosphonic acid derivative antibacterial approved for uncomplicated urinary tract infections (acute cystitis) in women. It comes as an oral granule packet dissolved in water and is taken as a single 3 g dose, rather than a multi-day course.
Keflex
Keflex (cephalexin) is a first-generation cephalosporin antibiotic used for infections like UTIs, skin infections, and respiratory infections. It is taken by mouth as a capsule, tablet, or liquid, typically several times a day for 7 to 14 days.
Fosfomycin vs. Keflex Side Effects
Fosfomycin
Keflex
Fosfomycin vs. Keflex Dosage
Fosfomycin
Keflex
| STAGE | DOSE | WHEN |
| Starting dose | 3 g single dose | At the start |
| Maximum dose | 3 g single dose | Same as starting |
| Dose changes | None | Fixed dose |
| 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 |
Fosfomycin
| STAGE | DOSE | WHEN |
| Starting dose | 3 g single dose | At the start |
| Maximum dose | 3 g single dose | Same as starting |
| Dose changes | None | Fixed dose |
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 |
Fosfomycin vs. Keflex Indications
Fosfomycin
Fosfomycin is FDA-approved only for uncomplicated urinary tract infections (acute cystitis) in women caused by susceptible E. coli or E. faecalis. It is not approved for pyelonephritis, complicated UTI, use in men, or children age 12 and under, though doctors sometimes prescribe it off-label for these situations.
Acute cystitis in women (FDA-approved)
Off-label: complicated UTI or pyelonephritis
Off-label: chronic bacterial prostatitis
Not approved for men or children 12 and under
Keflex
Keflex is FDA-approved for a broad range of bacterial infections, including respiratory tract infections, ear infections, skin infections, bone infections, and urinary tract infections. It is also used off-label to help prevent infection after certain surgeries.
Respiratory tract infections
Otitis media (ear infections)
Skin and skin structure infections
Bone infections
Fosfomycin vs. Keflex Pros and Cons
Fosfomycin
Fosfomycin's single-dose regimen makes it convenient and improves the odds patients complete treatment, but its FDA approval is narrow. It only covers uncomplicated cystitis in women, so more serious or complicated UTIs need a different antibiotic.
Pros
Single 3 g dose completes the entire treatment
No multi-day schedule of pills to remember
Repeat dosing hasn't been shown to work better, so one dose is standard
Shorter exposure may mean lower C. diff risk
Cons
Only FDA-approved for uncomplicated cystitis in women
Not effective for pyelonephritis or complicated UTI
Not approved for men or children 12 and under
Costs $80 to $145 per dose, more than a typical Keflex course
Keflex
Keflex covers a much wider range of infection types, but treatment requires taking doses multiple times a day for one to two weeks. Its decades of use mean prescribers are very familiar with its dosing and safety profile, though it carries its own risks.
Pros
FDA-approved for many infection types beyond UTI
Long track record of use since 1971
Costs $53 to $95 for a full course, less than one fosfomycin dose
Available as capsule, tablet, or liquid suspension
Cons
Requires multiple doses a day for 7 to 14 days
Risk of C. diff-associated diarrhea with longer courses
Seizure risk if it accumulates in kidney impairment
Contraindicated in patients allergic to cephalosporins
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