In a 72‑year‑old woman with congestive heart failure and hypertension, taking propranolol, atorvastatin and aspirin 150 mg, who has a recurrent Escherichia coli urinary tract infection resistant to prior amoxicillin and fosfomycin and a urine culture >100 000 CFU/mL while awaiting bladder ultrasound, what immediate management should be undertaken?

Immediate Management of Recurrent E. coli UTI with Antibiotic Resistance

Given the documented resistance to amoxicillin and fosfomycin with a bacterial count >100,000 CFU/mL, you should immediately obtain a urine culture with susceptibility testing before initiating empiric antibiotic therapy, then start treatment with either nitrofurantoin 100 mg orally twice daily for 5–7 days or trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days (if local E. coli resistance is <20% and she has not recently received this agent), while awaiting culture results to guide definitive therapy. 1

Diagnostic Workup Before Treatment

• Obtain a properly collected urine specimen (midstream clean-catch or in-and-out catheterization if contamination is suspected) for culture with antimicrobial susceptibility testing before starting antibiotics, as this is essential for guiding targeted therapy in recurrent UTI with documented resistance. 1

• Confirm both pyuria (≥10 WBC/HPF or positive leukocyte esterase) and acute urinary symptoms (dysuria, frequency, urgency, fever >38.3°C, or gross hematuria) are present before initiating treatment, as these are required diagnostic criteria. 1

• Process the specimen within 1 hour at room temperature or refrigerate within 4 hours to prevent bacterial overgrowth that could falsely elevate colony counts. 1

First-Line Empiric Antibiotic Selection

Preferred Option: Nitrofurantoin

• Nitrofurantoin 100 mg orally twice daily for 5–7 days is the preferred first-line agent because E. coli resistance rates remain <5%, urinary concentrations are high, and disruption of gut flora is minimal compared to fluoroquinolones. 1, 2

• Nitrofurantoin achieves excellent urinary concentrations with 97.4% sensitivity against E. coli in community-acquired UTI, making it highly effective even when other agents have failed. 3

• This agent is particularly appropriate given her normal renal function (eGFR 86 mL/min/1.73 m²), as nitrofurantoin is contraindicated when creatinine clearance <30 mL/min. 1

Alternative Option: Trimethoprim-Sulfamethoxazole

• Trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days may be used only if local E. coli resistance is <20% and she has not received this agent in the past 3 months. 1, 4

• E. coli sensitivity to trimethoprim-sulfamethoxazole is 68.3% in community settings, which falls below the ideal threshold but may be acceptable if susceptibility testing confirms sensitivity. 3

• The FDA label indicates this agent is appropriate for UTI caused by susceptible E. coli, Klebsiella, Enterobacter, Morganella morganii, and Proteus species, making it a reasonable empiric choice pending culture results. 4

Agents to Avoid

• Do not use fluoroquinolones (ciprofloxacin, levofloxacin) as first-line therapy because resistance rates approach 30% in community-acquired E. coli UTI, plus they cause substantial microbiome disruption and serious adverse effects (tendon rupture, peripheral neuropathy, QT prolongation). 1, 5

• Amoxicillin and amoxicillin-clavulanic acid should not be used empirically given E. coli sensitivity of only 41.9% and 83.8% respectively, plus documented prior amoxicillin failure in this patient. 3, 5

• Fosfomycin should not be repeated immediately given documented prior failure with this agent (received twice), though it may be reconsidered if culture shows susceptibility. 1

Special Considerations for This Patient

Cardiovascular Medications and Drug Interactions

• Propranolol does not directly cause thrombocytopenia, but the combination of aspirin 150 mg plus propranolol may increase bleeding risk; however, this should not delay UTI treatment. 1

• The low platelet count (not specified but implied) is more likely related to aspirin therapy rather than propranolol, and this does not contraindicate oral antibiotics. 1

Metabolic Abnormalities Requiring Attention

• The severe hypocalcemia (calcium 5.08 mg/dL, normal 8.5–10.5 mg/dL) requires urgent correction with intravenous calcium gluconate, as this level can cause cardiac arrhythmias and neuromuscular irritability. 6

• The elevated PTH (79.8 pg/mL) with low calcium and vitamin D deficiency (13.60 ng/mL) suggests secondary hyperparathyroidism, which should be addressed with vitamin D supplementation (cholecalciferol 50,000 IU weekly) after acute infection is treated. 6

• The hypomagnesemia (1.5 mg/dL, normal 1.7–2.2 mg/dL) should be corrected with oral magnesium supplementation, as this can worsen hypocalcemia and increase cardiac risk. 6

Recurrent UTI Risk Factors

• Postmenopausal status with high estradiol is unusual and warrants endocrine evaluation after acute infection resolves, as hormonal imbalances can affect urogenital flora. 1

• The positive family history of thyroid autoimmunity (anti-TG and anti-TPO in relative) does not directly increase UTI risk but suggests autoimmune predisposition that may require monitoring. 1

• Recurrent UTI (≥2 episodes in 6 months or ≥3 in 12 months) requires each episode to be documented with culture to monitor resistance patterns and guide prophylaxis decisions. 1

Management While Awaiting Bladder Ultrasound

• Do not delay antibiotic therapy while awaiting imaging results, as the bacterial count >100,000 CFU/mL with symptoms requires immediate treatment to prevent progression to pyelonephritis. 1

• The bladder ultrasound will help identify structural abnormalities (cystocele, bladder diverticula, high post-void residual) that predispose to recurrent UTI, but this does not change acute management. 7

• If fever >38.3°C, flank pain, nausea/vomiting, or inability to tolerate oral intake develop, this signals possible pyelonephritis requiring 7–14 days of therapy and consideration of parenteral antibiotics. 1

Reassessment and Follow-Up

• Re-evaluate clinical response within 48–72 hours; if symptoms persist or worsen, modify antibiotics according to culture susceptibility results and consider imaging (ultrasound or CT) to rule out obstruction, stones, or abscess. 1

• Adjust antibiotic therapy based on culture results as soon as susceptibility data are available, switching to the narrowest-spectrum agent that covers the isolated organism. 1

• No routine follow-up culture is needed if symptoms resolve completely, but given her recurrent UTI history, consider prophylactic strategies (vaginal estrogen if postmenopausal atrophy is present, behavioral modifications, or antibiotic prophylaxis) after acute infection clears. 1

Critical Pitfalls to Avoid

• Do not treat based solely on prior culture results without obtaining a new specimen, as resistance patterns can change between episodes and proper susceptibility testing is essential. 1

• Do not prescribe a 3-day course of nitrofurantoin; the minimum effective duration is 5 days to avoid treatment failure. 1

• Do not assume the sebaceous cyst is related to UTI, but monitor for signs of secondary infection given her recurrent infections and consider removal if it becomes symptomatic. 7

• Do not overlook the severe metabolic derangements (hypocalcemia, hypomagnesemia, vitamin D deficiency) while focusing on UTI, as these require concurrent management to prevent serious complications. 6