What is the cheapest antibiotic for an uncomplicated urinary tract infection in a non‑pregnant patient with normal renal function and no sulfa allergy?

Most Cost-Effective Antibiotic for Uncomplicated UTI

Trimethoprim-sulfamethoxazole (Bactrim) at 160/800 mg twice daily for 3 days is the least expensive antibiotic for uncomplicated UTI in women, provided local E. coli resistance rates are below 20%. 1, 2

First-Line Treatment Options by Cost

The most affordable first-line antibiotics for uncomplicated cystitis, in order of typical cost, are:

• Trimethoprim-sulfamethoxazole (Bactrim DS): 160/800 mg twice daily for 3 days 1, 2

  • Clinical cure rates of 90-100% when organisms are susceptible 2
  • Should NOT be used empirically if local E. coli resistance exceeds 20% 1, 2

• Trimethoprim alone: 200 mg twice daily for 5 days 1

  • Slightly less expensive than combination therapy in some regions 1
  • Not recommended in first trimester of pregnancy 1

• Nitrofurantoin: 100 mg twice daily for 5 days 1, 2

  • Achieves 90% clinical cure and 92% bacterial cure rates 2
  • Maintains excellent activity with resistance rates generally below 10% 2

• Fosfomycin trometamol: 3 g single dose 1, 2

  • More expensive but convenient single-dose therapy 2
  • Recommended only in women with uncomplicated cystitis 1

Critical Resistance Threshold

The 20% resistance threshold is crucial for decision-making. When E. coli resistance to trimethoprim-sulfamethoxazole exceeds 20%, treatment efficacy plummets from 84% to only 41-54%, making treatment failure the expected outcome. 2 At this point, the cost savings are negated by treatment failures requiring second courses of more expensive antibiotics.

When to Avoid Trimethoprim-Sulfamethoxazole

Avoid empiric use in patients who: 2

• Have used trimethoprim-sulfamethoxazole in the preceding 3-6 months
• Have traveled outside the United States in the preceding 3-6 months
• Live in areas where local resistance data shows >20% E. coli resistance
• Are in the last trimester of pregnancy 1

Treatment Duration Differences by Sex

• Women: 3 days of therapy is sufficient 1, 2, 3
• Men: 7 days of therapy is required for uncomplicated cystitis 1, 2, 3

The longer duration in men increases total cost but remains necessary for adequate treatment. 2

Cost-Effectiveness Considerations

Each additional day of antibiotic treatment beyond the recommended duration carries a 5% increased risk for antibiotic-associated adverse events without additional benefits. 2 This means that using longer courses to "ensure cure" actually increases both cost and harm without improving outcomes.

Common Pitfall to Avoid

Do not rely on hospital antibiograms for outpatient UTI treatment decisions. Hospital antibiograms often overestimate community resistance rates, and local outpatient surveillance data is more accurate for guiding empiric therapy in uncomplicated UTIs. 2 Using hospital data may lead you to unnecessarily avoid the least expensive option (trimethoprim-sulfamethoxazole) when it would actually be effective in your community.

Alternative When Cost is Secondary Concern

If trimethoprim-sulfamethoxazole cannot be used due to resistance patterns, nitrofurantoin 100 mg twice daily for 5 days is the next most cost-effective option with minimal resistance rates and excellent efficacy. 1, 2, 3