What is the recommended adult dose for an uncomplicated urinary tract infection (UTI)?

Adult Dosing for Uncomplicated UTI

For acute uncomplicated cystitis in adult women, prescribe nitrofurantoin 100 mg orally twice daily for 5 days as first-line therapy. 1

First-Line Treatment Options

The following agents are recommended as first-line therapy for uncomplicated UTI in women, listed in order of preference:

Nitrofurantoin (Preferred)

• Standard dose: 100 mg orally twice daily for 5 days 1
• Alternative duration: 5-7 days is acceptable, but do not exceed 7 days 1
• Maintains >95% susceptibility against E. coli isolates 1, 2
• Minimal disruption of normal flora compared to other agents 1
• Critical caveat: Never use for pyelonephritis or febrile UTI - it only concentrates in urine, not renal parenchyma 1

Trimethoprim-Sulfamethoxazole (TMP-SMX)

• Dose: 160/800 mg (one double-strength tablet) orally twice daily for 3 days 3, 4, 5
• Only use if local resistance rates are <20% 3
• Resistance rates average 29% in many communities, limiting its utility 2

Fosfomycin

• Dose: 3 g orally as a single dose 4, 5
• Convenient single-dose regimen 4
• May have slightly inferior efficacy compared to other first-line agents 3

Trimethoprim Alone

• Dose: 100 mg orally twice daily for 3 days 5
• Appropriate when TMP-SMX cannot be used 5

Second-Line and Alternative Agents

Fluoroquinolones (Reserve for Complicated Infections)

• Ciprofloxacin: 250 mg orally twice daily for 3 days 3
• Levofloxacin: 250 mg orally once daily for 3 days 3
• Highly efficacious but should be reserved for pyelonephritis and complicated UTIs, not simple cystitis 3
• Resistance rates now approach 24% for E. coli 2

Beta-Lactams (Use Only When First-Line Agents Cannot Be Used)

• Amoxicillin-clavulanate, cefdinir, cefaclor, or cefpodoxime-proxetil: 3-7 days 3
• Inferior efficacy and more adverse effects compared to first-line agents 3
• Never use amoxicillin or ampicillin alone - very high resistance rates worldwide 3

Special Populations

Men with Uncomplicated UTI

• Always obtain urine culture before treatment 5
• First-line options: TMP-SMX, trimethoprim, or nitrofurantoin for 7 days (not 3-5 days as in women) 5
• Consider urethritis and prostatitis in the differential diagnosis 5
• Limited evidence supports 7-14 days of therapy 4

Women with Diabetes

• Treat identically to women without diabetes if no voiding abnormalities are present 4
• Same first-line agents and durations apply 4

Adults ≥65 Years Old

• Obtain urine culture with susceptibility testing 5
• Same first-line antibiotics and durations as younger adults 5
• Adjust empiric therapy based on culture results 5

Common Pitfalls to Avoid

• Do not use nitrofurantoin for pyelonephritis - this is the most common prescribing error, as it achieves inadequate tissue concentrations outside the bladder 1
• Do not extend treatment beyond 7 days for simple cystitis - increases adverse events without additional benefit 1
• Do not use fluoroquinolones as first-line for simple cystitis - reserve for more serious infections to preserve efficacy 3
• Do not prescribe amoxicillin or ampicillin empirically - resistance rates are too high 3
• Do not treat men with 3-day regimens - they require 7-14 days of therapy 4, 5