Bactrim vs. Fosfomycin
See how Bactrim and Fosfomycin compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Bactrim treats a much wider range of infections than fosfomycin, including respiratory, skin, and gastrointestinal infections, while fosfomycin is only approved for uncomplicated UTIs in women.
Fosfomycin is taken as a single 3-gram dose, while Bactrim typically requires twice-daily dosing for several days depending on the infection.
Bactrim costs less per month than a single dose of fosfomycin, but it carries more warnings around allergic reactions, blood disorders, and pregnancy use.
Bactrim vs. Fosfomycin Drug Summary
Bactrim
Bactrim is a combination antibacterial containing sulfamethoxazole and trimethoprim, used to treat urinary tract infections, certain types of pneumonia, and several other bacterial infections. It works by blocking two sequential steps in bacterial folate production, and it is taken orally as a tablet or liquid, or given by IV for more severe infections.
Fosfomycin
Fosfomycin is an antibacterial in its own drug class, approved for treating uncomplicated urinary tract infections in women caused by susceptible E. coli or E. faecalis. It is taken as a single 3-gram dose of oral granules dissolved in water, with no multi-day course required.
Bactrim vs. Fosfomycin Side Effects
Bactrim
Fosfomycin
Bactrim vs. Fosfomycin Dosage
Bactrim
Fosfomycin
| STAGE | DOSE | WHEN |
| Starting dose | 800 mg/160 mg every 12h | At the start |
| Maximum dose | 8-10 mg/kg/day div q6-12h | If needed |
| Dose changes | 3 increases | As tolerated |
| 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 |
Bactrim
| STAGE | DOSE | WHEN |
| Starting dose | 800 mg/160 mg every 12h | At the start |
| Maximum dose | 8-10 mg/kg/day div q6-12h | 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 |
Bactrim vs. Fosfomycin Indications
Bactrim
Bactrim is FDA-approved for urinary tract infections, along with several other bacterial infections that affect different parts of the body. It also treats ear infections in children, traveler's diarrhea, and pneumocystis pneumonia, and it is sometimes used off-label for MRSA skin infections.
Urinary tract infections
Acute otitis media in children
Traveler's diarrhea in adults
Pneumocystis jirovecii pneumonia
Off-label: MRSA skin infections
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 sometimes used off-label for complicated UTIs or chronic prostatitis, but it is not approved for pyelonephritis, men, or children under 12.
Uncomplicated UTI in women only
Caused by E. coli or E. faecalis
Off-label: complicated UTI/pyelonephritis
Off-label: chronic bacterial prostatitis
Not approved for men or children
Bactrim vs. Fosfomycin Pros and Cons
Bactrim
Bactrim's broad approval across infection types and low cost make it a common first-line choice for many bacterial infections, including UTIs. Its main drawbacks are the multi-day dosing schedule and a higher chance of allergic or blood-related side effects.
Pros
Treats many infection types beyond UTIs
Available as tablet, liquid, or IV
Inexpensive, roughly $10 to $30 per month
Multiple dosing options for different severities
Cons
Requires twice-daily dosing for several days
Higher risk of severe skin reactions
Unsafe in pregnancy and G6PD deficiency
Contraindicated in infants under 2 months
Fosfomycin
Fosfomycin's single-dose regimen makes it appealing for patients who want a simple, one-time treatment for uncomplicated cystitis. Its narrower approval and higher per-course cost limit its use to a specific patient population.
Pros
Single-dose treatment, no multi-day course
Simple regimen improves adherence
No boxed warning
Fewer drug interaction concerns
Cons
Only approved for uncomplicated UTI in women
Not effective for pyelonephritis or complicated UTI
Costs roughly $80 to $145 per single dose
Not approved for men or children under 12
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