Open Forum Infectious Diseases (OFID)Safety of Fluoroquinolones and Cotrimoxazole in Urinary Tract Infections in Older Males

⚠️ Small Study / Early Comparative Evidence

A retrospective study of 228 hospitalized men aged 75 or older with urinary tract infections found cotrimoxazole associated with significantly higher adverse event rates than fluoroquinolones, driven by acute kidney injury and metabolic disorders. Authors call for prospective confirmation; findings do not yet override current fluoroquinolone restriction guidance.

Pharmacist Considerations

• Cotrimoxazole produced AEs in 48.5% of patients vs 29.7% on fluoroquinolones (adjusted OR 2.10; 95% CI, 1.18–3.74), with AE-driven treatment discontinuation nearly five times higher on cotrimoxazole (11.3% vs 2.3%).
• AKI was the dominant event, occurring in 29.4% of cotrimoxazole patients vs 7.2% on fluoroquinolones (P<.001), with median onset at 6 days, beyond standard post-initiation monitoring windows in most discharge protocols.
• Cotrimoxazole metabolic risks, including hyperkalemia, hyponatremia, and hypoglycemia, were compounded in a cohort where 59.2% were already on nephrotoxic agents including ACE inhibitors, ARBs, and diuretics.
• Cotrimoxazole’s CYP450 inhibition creates clinically significant interaction risk with vitamin K antagonists and oral antidiabetics in a population carrying a median of 7 medications per day.

Practice Applications

• Monitor renal function and electrolytes for at least 6 days after cotrimoxazole initiation in men aged 75 or older; standard 48–72-hour checks are insufficient based on observed AKI onset timing.
• Screen for concurrent ACE inhibitors, ARBs, diuretics, anticoagulants, and oral antidiabetics before dispensing or verifying cotrimoxazole in this population.
• Flag orders pairing cotrimoxazole with vitamin K antagonists or sulfonylureas for prescriber review; interaction risk is amplified by the polypharmacy baseline in geriatric patients.
• Recognize that FDA and EMA fluoroquinolone restriction guidance remains in effect for nonsevere UTI; this retrospective study generates a hypothesis and does not reverse regulatory labeling.

Counseling Anchors

• Patients and caregivers should report new fatigue, decreased urination, muscle weakness, or confusion within the first week of either antibiotic; these may be early signs of kidney injury or electrolyte disturbance.
• Patients on blood thinners or diabetes medications need explicit counseling that cotrimoxazole can amplify the effects of both; monitoring may need to be accelerated.