In an otherwise healthy adult with uncomplicated urinary‑tract infection (cystitis) and no sulfonamide allergy or renal impairment, how many days should Bactrim (trimethoprim‑sulfamethoxazole) be taken?

Bactrim Duration for Uncomplicated UTI

For an otherwise healthy adult woman with uncomplicated cystitis, prescribe Bactrim (trimethoprim-sulfamethoxazole) 160/800 mg (one double-strength tablet) twice daily for 3 days, provided local E. coli resistance is below 20%. 1, 2

Sex-Specific Duration Requirements

• Women with uncomplicated cystitis require 3 days of Bactrim DS (160/800 mg) twice daily, achieving clinical cure rates of 90–100% when organisms are susceptible. 1, 2

• Men with uncomplicated cystitis require 7 days of Bactrim DS (160/800 mg) twice daily because short-course therapy is inadequate in males. 1

Critical Resistance Threshold

• Do not prescribe Bactrim empirically when local E. coli resistance exceeds 20%, as clinical cure rates plummet from 84–100% (susceptible organisms) to only 41–54% (resistant organisms), making treatment failure the expected outcome. 1, 2

• Patients who have used Bactrim within the preceding 3–6 months should not receive it again, as recent exposure independently predicts resistance. 1

• Patients who have traveled outside the United States within the preceding 3–6 months should avoid empiric Bactrim due to higher rates of resistant uropathogens. 1

Alternative First-Line Agents (When Bactrim Is Unsuitable)

When local resistance is ≥20%, recent Bactrim exposure exists, or resistance data are unavailable, use these alternatives:

• Nitrofurantoin monohydrate/macrocrystals 100 mg twice daily for 5 days achieves 90% clinical cure and 92% bacterial cure rates with minimal resistance (generally <10%). 1, 3, 4

• Fosfomycin trometamol 3 g as a single dose offers convenient single-dose therapy with comparable efficacy, though slightly lower bacteriological cure than multi-day regimens. 1, 4

• Fluoroquinolones (ciprofloxacin 250 mg twice daily for 3 days) should be reserved for pyelonephritis or when first-line agents cannot be used, due to FDA warnings about tendon rupture, peripheral neuropathy, and collateral damage to normal flora. 1, 4

Common Pitfalls to Avoid

• Never use the 3-day regimen in men—they require 7 days for adequate cure. 1

• Do not rely on hospital antibiograms for community-acquired cystitis; they overestimate resistance because they reflect complicated infections. Outpatient surveillance data are more accurate. 1

• Avoid prescribing Bactrim without knowing local resistance rates, as many communities now exceed the 20% threshold, rendering empiric use inappropriate. 1, 2

• Do not use amoxicillin or ampicillin for uncomplicated UTI; worldwide E. coli resistance to these agents exceeds 55–67%. 1

Pregnancy and Special Populations

• Avoid Bactrim in the last trimester of pregnancy due to potential fetal risks. 1

• Avoid Bactrim in patients with marked hepatic damage, as it may exacerbate the condition. 1

• For patients with creatinine clearance 15–30 mL/min, use half the usual dose; Bactrim is not recommended when creatinine clearance is below 15 mL/min. 5

When to Obtain Urine Culture

• Do not obtain routine culture for straightforward uncomplicated cystitis in otherwise healthy women. 1

• Obtain culture and susceptibility testing when:

  • Symptoms persist after completing therapy
  • Symptoms recur within 2–4 weeks
  • Fever, flank pain, or systemic signs suggest pyelonephritis
  • Pregnancy (any trimester)
  • Atypical presentation 1

Management of Treatment Failure

• If symptoms have not resolved by day 3 or recur within 2 weeks, obtain urine culture immediately and switch to a different antibiotic class for a full 7-day course (do not repeat a short-course regimen). 1

• The presumptive cause of failure is resistance; alternative agents include nitrofurantoin, fosfomycin, or a fluoroquinolone based on culture results. 1