What is the recommended treatment for uncomplicated cystitis (lower urinary‑tract infection) in a teenage female?

Treatment for Cystitis and UTI in Teenage Females

For uncomplicated cystitis in a teenage female, prescribe nitrofurantoin 100 mg orally twice daily for 5 days as the preferred first-line agent, achieving approximately 93% clinical cure with minimal resistance and low collateral damage to intestinal flora. 1

First-Line Antibiotic Options

Nitrofurantoin (Preferred)

• Nitrofurantoin 100 mg orally twice daily for 5 days provides 93% clinical cure and 88% microbiological eradication, with worldwide resistance rates below 1%. 1
• This agent causes minimal disruption of intestinal microbiota compared to fluoroquinolones and cephalosporins, thereby reducing the risk of Clostridioides difficile infection. 1
• Contraindication: Do not use if estimated glomerular filtration rate (eGFR) is <30 mL/min/1.73 m², as therapeutic urinary concentrations cannot be achieved. 1

Trimethoprim-Sulfamethoxazole (TMP-SMX)

• TMP-SMX 160/800 mg orally twice daily for 3 days achieves 93% clinical cure and 94% microbiological eradication when the pathogen is susceptible. 1
• Use only when BOTH criteria are met: (1) local E. coli resistance is <20%, AND (2) the patient has not received TMP-SMX in the preceding 3 months. 1, 2
• Many regions now report TMP-SMX resistance exceeding 20%, making verification of local antibiogram data mandatory before selection. 1

Fosfomycin

• Fosfomycin 3 g as a single oral dose provides approximately 91% clinical cure, with therapeutic urinary concentrations maintained for 24–48 hours. 1
• The single-dose regimen improves adherence compared to multi-day courses. 1
• Initial-infection resistance rates are approximately 2.6%. 1
• Do not use for suspected pyelonephritis or upper urinary tract infections due to insufficient tissue penetration. 1

When Urine Culture Is Required

Routine urine culture is NOT needed for typical uncomplicated cystitis. 3 Obtain culture and susceptibility testing only when:

• Persistent symptoms after completing the prescribed regimen 1
• Recurrence of symptoms within 2–4 weeks 1, 4
• Fever >38°C, flank pain, or costovertebral angle tenderness suggesting pyelonephritis 1
• Atypical presentation or presence of vaginal discharge 1, 4
• History of recurrent infections or prior isolation of resistant organisms 1

Reserve (Second-Line) Agents – Use Only After First-Line Failure

Fluoroquinolones

• Ciprofloxacin 250–500 mg twice daily or levofloxacin 250–750 mg once daily for 3 days should be reserved exclusively for culture-proven resistant pathogens or documented failure of first-line therapy. 1
• The FDA warns that serious adverse effects (tendon rupture, peripheral neuropathy, CNS toxicity) outweigh benefits for uncomplicated UTIs. 1
• Global fluoroquinolone resistance is rising, with some regions reporting >10% resistance among uropathogens. 1, 5

Beta-Lactams

• Amoxicillin-clavulanate, cefdinir, or cefpodoxime for 3–7 days achieve only 89% clinical cure and 82% microbiological eradication, significantly inferior to first-line agents. 1
• Never use amoxicillin or ampicillin alone because worldwide E. coli resistance exceeds 55–67%. 1

Treatment Algorithm

1. Confirm uncomplicated cystitis: Lower urinary tract symptoms (dysuria, frequency, urgency) without fever, flank pain, pregnancy, catheter, immunosuppression, or recent instrumentation. 1

2. Assess local TMP-SMX resistance:

   • If <20% AND no recent TMP-SMX use → prescribe TMP-SMX 160/800 mg twice daily for 3 days. 1, 2
   • If ≥20% OR local data unavailable → prescribe nitrofurantoin 100 mg twice daily for 5 days or fosfomycin 3 g single dose. 1

3. If symptoms persist after 2–3 days or recur within 2 weeks:

   • Obtain urine culture and susceptibility testing immediately. 1
   • Switch to a different antibiotic class for a 7-day course (not the original short regimen). 1
   • Reserve fluoroquinolones only for culture-proven resistance. 1

Critical Pitfalls to Avoid

• Do not treat asymptomatic bacteriuria in non-pregnant, non-catheterized teenagers, as this promotes resistance without clinical benefit. 1, 3
• Do not use empiric fluoroquinolones as first-line therapy for uncomplicated cystitis because of serious adverse effects and rising resistance. 1, 3
• Do not prescribe TMP-SMX without confirming local resistance is <20%; failure rates increase sharply above this threshold. 1
• Do not use nitrofurantoin for suspected pyelonephritis (fever, flank pain) or when eGFR <30 mL/min/1.73 m². 1
• Do not perform routine post-treatment urinalysis or cultures in asymptomatic patients. 3

Management of Treatment Failure

• If symptoms have not resolved by the end of therapy or recur within 2 weeks, obtain urine culture and susceptibility testing immediately. 1
• Assume the original pathogen is resistant to the previously used agent and switch to a different antibiotic class for a full 7-day course. 1
• If fever persists beyond 72 hours, perform renal ultrasound or CT imaging to exclude obstruction or abscess. 1