What is the appropriate curative antibiotic regimen for an acute recurrent post‑coital cystitis (uncomplicated lower urinary‑tract infection) in a non‑pregnant adult with normal renal function?

Treatment of Acute Recurrent Post-Coital Cystitis (Curative Therapy)

For an acute episode of post-coital cystitis requiring curative treatment, prescribe fosfomycin trometamol 3 g as a single oral dose, nitrofurantoin 100 mg twice daily for 5 days, or trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days (only if local E. coli resistance is <20%). 1

First-Line Curative Antibiotic Regimens

Fosfomycin Trometamol (Preferred Single-Dose Option)

• Dosing: 3 g as a single oral dose 1
• Efficacy: Achieves 82% microbiologic eradication at 5-11 days post-therapy and 70% sustained eradication at 12-21 days 2
• Advantages: Single-dose convenience improves adherence, maintains therapeutic urinary concentrations for 24-48 hours, and causes minimal disruption to intestinal flora 1, 3
• Limitations: Slightly inferior bacteriological efficacy compared to 3-day trimethoprim-sulfamethoxazole (82% vs 98% at 5-11 days), though clinical outcomes remain acceptable 2

Nitrofurantoin (Preferred Multi-Day Option)

• Dosing: 100 mg orally twice daily for 5 days 1
• Efficacy: Achieves 76-77% microbiologic eradication, equivalent to fosfomycin 2
• Advantages: Excellent activity against E. coli (responsible for 75-95% of cases), worldwide resistance rates <1%, minimal collateral damage to gut flora 1, 3
• Contraindication: Avoid if eGFR <30 mL/min/1.73 m² 3

Trimethoprim-Sulfamethoxazole (Conditional First-Line)

• Dosing: 160/800 mg orally twice daily for 3 days 1
• Efficacy: Achieves 98% microbiologic eradication at 5-11 days and 94% sustained eradication at 12-21 days 2
• Critical restriction: Use only when local E. coli resistance is documented to be <20% 1, 4
• Additional restriction: Avoid if the patient received trimethoprim-sulfamethoxazole within the preceding 3 months 3

Alternative (Second-Line) Regimens

Fluoroquinolones (Reserve for Resistant Organisms)

• Ciprofloxacin 250 mg twice daily for 3 days achieves 98% microbiologic eradication 2
• Reserve exclusively for culture-proven resistant pathogens or documented failure of first-line therapy 1, 3
• Rationale for restriction: Serious adverse effects (tendon rupture, C. difficile infection), rising global resistance rates, and need to preserve efficacy for life-threatening infections 3

Beta-Lactams (Inferior Efficacy)

• Cephalosporins (e.g., cefadroxil 500 mg twice daily for 3 days) may be used when local E. coli resistance is <20% 1
• Avoid amoxicillin or ampicillin alone due to poor efficacy and high resistance rates 3

Diagnostic Approach for This Acute Episode

When Urine Culture Is NOT Required

• Typical lower urinary tract symptoms (dysuria, frequency, urgency) without vaginal discharge in an otherwise healthy woman 1
• No fever, flank pain, or systemic symptoms 1

When Urine Culture IS Mandatory

• Symptoms persist at the end of treatment 1
• Symptoms recur within 2-4 weeks after completion 1
• Atypical presentation or presence of vaginal discharge 1
• Fever, flank pain, or other signs suggesting pyelonephritis 1

Management of Treatment Failure

• If symptoms do not resolve by the end of treatment or recur within 2 weeks, obtain urine culture and antimicrobial susceptibility testing immediately 1
• Assume the infecting organism is not susceptible to the agent originally used 1
• Retreat with a 7-day regimen using a different antibiotic class 1

Critical Clinical Pitfalls to Avoid

• Do not use fosfomycin for suspected pyelonephritis (fever, flank pain, costovertebral angle tenderness)—it lacks efficacy data for upper tract infections 3
• Do not prescribe empiric fluoroquinolones for uncomplicated cystitis—reserve them for documented resistance 1, 3
• Do not use trimethoprim-sulfamethoxazole empirically without verifying local resistance is <20%; if data are unavailable, default to nitrofurantoin or fosfomycin 1, 4
• Do not treat asymptomatic bacteriuria in non-pregnant women—this promotes resistance without clinical benefit 1
• Routine post-treatment urinalysis or urine cultures are not indicated for asymptomatic patients who complete therapy successfully 1

Post-Coital Prophylaxis Consideration (Not Curative)

While you specifically requested curative treatment, note that for women with recurrent post-coital cystitis (≥3 episodes per year or 2 episodes in 6 months), post-coital prophylactic antibiotics are as effective as continuous daily prophylaxis and use fewer antibiotics overall 5, 6, 7. This strategy should be discussed after the acute episode resolves.