Fosfomycin vs. Trimethoprim
See how Fosfomycin and Trimethoprim compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Fosfomycin treats uncomplicated UTIs with one 3 g dose, while trimethoprim requires a 10-day course of twice- or once-daily tablets.
Both drugs are FDA-approved only for uncomplicated cystitis in adults and should not be used for pyelonephritis or complicated UTI.
Trimethoprim carries risks not shared by fosfomycin, including hyperkalemia, blood cell disorders, and severe skin reactions like Stevens-Johnson syndrome.
Fosfomycin vs. Trimethoprim Drug Summary
Fosfomycin
Fosfomycin is a phosphonic acid derivative antibacterial used for uncomplicated urinary tract infections in women. It comes as oral granules mixed with water and taken as a single 3 g dose. Repeating the dose has not been shown to work better and raises the chance of side effects.
Trimethoprim
Trimethoprim is a urinary anti-infective that blocks bacterial folate production to treat acute uncomplicated UTIs. It is taken as a 100 mg tablet every 12 hours or a 200 mg tablet once daily for 10 days. Because it does not contain a sulfonamide, it can be used in some patients with sulfa allergies.
Fosfomycin vs. Trimethoprim Side Effects
Fosfomycin
Trimethoprim
Fosfomycin vs. Trimethoprim Dosage
Fosfomycin
Trimethoprim
| 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 | 100 mg every 12 hours | Days 1-10 |
| Maximum dose | 200 mg once daily | Days 1-10 |
| Dose changes | 1 increase | 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 |
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 |
Fosfomycin vs. Trimethoprim Indications
Fosfomycin
Fosfomycin is FDA-approved for uncomplicated UTIs (acute cystitis) in women caused by susceptible E. coli or E. faecalis. It is not approved for men, children 12 and under, or pyelonephritis. Doctors sometimes use it off-label, in repeated doses, for complicated UTI or chronic prostatitis.
FDA-approved for uncomplicated cystitis in women
Off-label for complicated UTI or pyelonephritis (multi-dose)
Off-label for chronic bacterial prostatitis
Not approved for men or children 12 and under
Trimethoprim
Trimethoprim is FDA-approved for acute uncomplicated UTIs caused by susceptible E. coli, Proteus, Klebsiella, Enterobacter, or coagulase-negative staphylococci. It is not approved for infants under 2 months old. Off-label, it is used to prevent recurrent UTIs and, combined with dapsone, to prevent Pneumocystis pneumonia.
FDA-approved for acute uncomplicated UTIs
Off-label for recurrent UTI prevention
Off-label PCP prophylaxis with dapsone
Not approved for infants under 2 months
Fosfomycin vs. Trimethoprim Pros and Cons
Fosfomycin
Fosfomycin's single-dose regimen makes it a convenient option when finishing a multi-day antibiotic course is a concern. It costs more per treatment than generic trimethoprim and is not an option for men or complicated infections.
Pros
Single 3 g dose completes the full treatment
No multi-day dosing schedule to remember
Effective against some E. coli resistant to other antibiotics
Fewer drug interaction concerns than many antibiotics
Cons
Not approved for pyelonephritis or complicated UTI
Not approved for men or children 12 and under
Costs more per treatment, roughly $80 to $145 per dose versus $45 to $75 for trimethoprim's full course
Higher reported rates of diarrhea and headache
Trimethoprim
Trimethoprim has decades of clinical use and a lower cost, but requires a full 10-day course to complete treatment. It carries warnings for hyperkalemia, blood disorders, and severe skin reactions that are not associated with fosfomycin.
Pros
Lower cost, roughly $45 to $75 for a full 10-day course versus $80 to $145 for fosfomycin
Option for patients with sulfa allergy since it lacks a sulfonamide
Flexible dosing: once or twice daily options
Long track record of use since 1980
Cons
Requires a full 10-day course rather than one dose
Risk of hyperkalemia, including in patients without risk factors
Risk of blood disorders like megaloblastic anemia
Risk of severe skin reactions including Stevens-Johnson syndrome
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