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

Most common
Vomiting (not specified)
Nausea (not specified)
Rash (not specified)
Anorexia (not specified)

Trimethoprim

Most common
Vomiting (not specified)
Nausea (not specified)
Rash (up to 6.7%)
Pruritus (not specified)

Bactrim vs. Trimethoprim Dosage

Bactrim

Dosage
Dosage Table
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

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

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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