For a CrCl of 15-29 mL/min, what is the recommended action for sulfamethoxazole-trimethoprim?

• A. Reduce dosage
• B. Avoid entirely
• C. Increase dose
• D. No adjustment

Answer: (A)

In renal impairment, drugs cleared by the kidneys need dosing adjustments to prevent buildup and toxicity. Sulfamethoxazole-trimethoprim is eliminated primarily by the kidneys, so when the creatinine clearance is in the 15–29 mL/min range, clearance is substantially reduced. Giving the standard dose would raise drug exposure and increase risks such as hyperkalemia from trimethoprim, bone marrow suppression, and nephrotoxicity, among others. Therefore, the safest and most appropriate approach is to reduce the dose (or extend the dosing interval) to maintain therapeutic effect while minimizing adverse effects. Increasing the dose would worsen accumulation, and not adjusting would raise toxicity risk; avoiding entirely is typically reserved for more severe renal impairment or higher risk scenarios, whereas a measured dose reduction is appropriate here. Monitor renal function and electrolytes and adjust as function changes.