In an 81-year-old woman with recurrent urinary-tract infection symptoms shortly after completing a 7-day course of amoxicillin-clavulanate, estimated glomerular filtration rate 94 mL/min, creatinine 0.51 mg/dL, and blood urea nitrogen 41 mg/dL, what is the most appropriate next step in management?

Management of Recurrent UTI After Failed Augmentin Therapy

Obtain a urine culture with antimicrobial susceptibility testing immediately before initiating any new antibiotic, then switch to nitrofurantoin 100 mg twice daily for 7 days as the preferred empiric agent while awaiting culture results. 1, 2

Immediate Diagnostic Steps

• Urine culture with susceptibility testing is mandatory when symptoms persist or recur within 2 weeks of completing antimicrobial therapy, as this represents either treatment failure or rapid reinfection requiring culture-directed therapy 1, 2

• The patient's normal renal function (GFR 94 mL/min, creatinine 0.51 mg/dL) permits use of all standard UTI antibiotics without dose adjustment 2

• Amoxicillin-clavulanate demonstrates significantly inferior efficacy compared to other first-line agents, with clinical cure rates of only 58% versus 77% for ciprofloxacin in head-to-head trials 1

Empiric Re-Treatment While Awaiting Culture

First-line empiric choice:

• Nitrofurantoin 100 mg orally twice daily for 7 days is the preferred agent for re-treatment, offering minimal resistance patterns, low collateral damage to normal flora, and high urinary concentrations 1, 2

• Trimethoprim-sulfamethoxazole 160/800 mg twice daily for 7 days is an acceptable alternative only if local resistance rates are <20% or if prior cultures showed susceptibility 1, 2, 3

Avoid fluoroquinolones as empiric therapy unless other agents cannot be used, as they should be reserved for complicated infections or pyelonephritis to preserve efficacy and minimize resistance 1, 2

Culture-Directed Therapy Adjustment

• Once susceptibility results return, tailor therapy to the specific organism and resistance pattern 1

• If the organism shows resistance to amoxicillin-clavulanate but susceptibility to nitrofurantoin, continue the nitrofurantoin course for the full 7 days 2

• If the organism is resistant to nitrofurantoin, switch to any other antimicrobial class demonstrating susceptibility on the panel 2

Evaluation for Complicating Factors

Assess for features suggesting complicated UTI requiring imaging or urologic evaluation:

• Rapid recurrence with the same organism (within 2 weeks) suggests bacterial persistence from underlying structural abnormalities such as bladder/urethral diverticula, calculi, incomplete bladder emptying, or foreign bodies 1

• Risk factors warranting imaging include: prior urinary tract surgery/trauma, gross hematuria after infection resolution, urea-splitting bacteria on culture, prior abdominopelvic malignancy, prior urinary calculi, symptoms of pneumaturia or fecaluria 1

• Postmenopausal women are at increased risk for recurrent UTI in the presence of urinary incontinence, cystocele, or high postvoid residual volumes 1

Prevention Strategies for Recurrent UTI

This patient meets criteria for recurrent UTI (≥3 episodes per year or ≥2 in 6 months) and should receive preventive interventions: 1, 2

• Vaginal estrogen therapy (for postmenopausal women) reduces future UTI risk with moderate-quality evidence 2, 4

• Behavioral modifications: adequate hydration to promote frequent urination, urge-initiated voiding, post-coital voiding if sexually active, avoidance of spermicidal-containing contraceptives 1

• Antibiotic prophylaxis (nitrofurantoin 50-100 mg daily for 6-12 months) may be considered after acute infection resolves, though this increases resistance risk and should be approached judiciously 1, 2

• Non-antibiotic alternatives: methenamine hippurate, lactobacillus-containing probiotics, or cranberry products in tolerable formulations 2

Critical Pitfalls to Avoid

• Do not treat asymptomatic bacteriuria if cultures show bacteria but symptoms have resolved, as this paradoxically increases antimicrobial resistance and recurrent UTI rates 2, 5

• Do not perform routine post-treatment cultures in asymptomatic patients, as this leads to unnecessary treatment of colonization rather than infection 2

• Do not automatically classify as "complicated UTI" unless true complicating factors exist (structural abnormalities, immunosuppression, pregnancy, diabetes with poor control), as misclassification leads to unnecessary broad-spectrum antibiotics with prolonged treatment durations 1, 2

• Avoid β-lactams as first-line therapy for recurrent UTI given their inferior efficacy (60% cure rate for amoxicillin-clavulanate versus 95% for other agents) and higher adverse effect rates 1