Bactrim vs. Trimethoprim
See how Bactrim and Trimethoprim compare on approved uses, dosing, side effects, and cost.
Key Takeaways
Bactrim combines two antibacterials and is FDA-approved for infections ranging from UTIs to pneumocystis pneumonia, while trimethoprim alone is approved only for uncomplicated UTIs.
Trimethoprim lacks the sulfonamide found in Bactrim, making it a common alternative for patients with a sulfa allergy.
Both drugs carry warnings for hyperkalemia and severe skin reactions, so either one calls for monitoring, especially in older adults or those with kidney problems.
Bactrim vs. Trimethoprim Drug Summary
Bactrim
Bactrim is a combination sulfonamide antibacterial that pairs sulfamethoxazole with trimethoprim to block two sequential steps in bacterial folate production. It treats urinary tract infections, pneumocystis pneumonia, shigellosis, and several other infections. It comes as a tablet, oral suspension, or IV injection, typically taken every 12 hours.
Trimethoprim
Trimethoprim is a single-agent urinary anti-infective that blocks the same folate synthesis step as the trimethoprim component in Bactrim. It is FDA-approved only for treating acute uncomplicated urinary tract infections caused by susceptible bacteria. It is taken as an oral tablet once or twice daily, usually for 10 days.
Bactrim vs. Trimethoprim Side Effects
Bactrim
Trimethoprim
Bactrim vs. Trimethoprim Dosage
Bactrim
Trimethoprim
| 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 | 100 mg every 12 hours | Days 1-10 |
| Maximum dose | 200 mg once daily | Days 1-10 |
| Dose changes | 1 increase | As tolerated |
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 |
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 |
Bactrim vs. Trimethoprim Indications
Bactrim
Bactrim is FDA-approved for a wide range of bacterial infections, from urinary tract infections to pneumocystis pneumonia. It is also used for shigellosis, pediatric ear infections, bronchitis flare-ups, and traveler's diarrhea in adults.
Urinary tract infections
Pneumocystis jirovecii pneumonia (treatment and prevention)
Shigellosis
Trimethoprim
Trimethoprim's FDA approval covers only acute uncomplicated urinary tract infections caused by susceptible bacteria. Doctors also prescribe it off-label to prevent recurrent UTIs and, paired with dapsone, to prevent pneumocystis pneumonia.
Acute uncomplicated UTI (E. coli, Proteus, others)
Recurrent UTI prevention (off-label)
PCP prophylaxis with dapsone (off-label)
Bactrim vs. Trimethoprim Pros and Cons
Bactrim
Bactrim's combination of two antibacterials gives it a broader set of FDA-approved uses and more dosage forms, but its sulfonamide component rules it out for patients with a sulfa allergy. It has a long history of use and remains one of the least expensive antibiotics on the market.
Pros
FDA-approved for a much wider range of infections, including PCP pneumonia and shigellosis
Available as tablets, oral suspension, and IV injection for flexible dosing
Roughly $10 to $30 per month, one of the least expensive antibiotics available
Cons
Contains a sulfonamide, so it cannot be used by patients with a sulfa allergy
Combination of two drugs means more potential drug interactions than trimethoprim alone
Pediatric dosing can require more frequent dosing, such as every 6 hours
Trimethoprim
Trimethoprim works as a single agent without the sulfonamide found in Bactrim, making it a useful option for patients who cannot tolerate sulfa drugs, but its FDA approval is limited to uncomplicated UTIs. It typically costs more per course than Bactrim and comes only as an oral tablet.
Pros
Lacks the sulfonamide component, making it an option for patients with a sulfa allergy
Simple once- or twice-daily dosing with a single tablet strength
Fewer sulfa-related interaction concerns since it is not combined with a sulfonamide
Cons
FDA-approved only for uncomplicated UTIs, a much narrower label than Bactrim
Roughly $45 to $75 for a typical 10-day course, pricier than Bactrim
Can interfere with certain lab tests, including creatinine and methotrexate assays
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