A 55-year-old male (weight 95 kg) comes to the pharmacy after a dental procedure and asks what he can take for pain. His current medications: lisinopril 40 mg once daily, chlorthalidone 25 mg once daily, and naproxen 500 mg twice daily that he has been taking for chronic back pain; he also takes OTC ibuprofen 200 mg tablets "sometimes on top of naproxen" and a daily multivitamin. Labs from last week: serum creatinine 1.6 mg/dL (elevated; reference 0.6–1.3), potassium 4.7 mEq/L, alanine aminotransferase 19 U/L. Medical history: hypertension, chronic back pain, chronic kidney disease stage 3. Allergies: none. What is the most concerning interaction in this patient's regimen?
- Lisinopril plus chlorthalidone causing dangerously high potassium
- Naproxen plus ibuprofen causing additive nonsteroidal anti-inflammatory drug toxicity and increased kidney injury risk (correct answer)
- Multivitamin plus chlorthalidone causing severe hypoglycemia
- Lisinopril plus multivitamin causing acute hepatotoxicity
Explanation: This question evaluates recognition of nephrotoxic drug combinations during medication reconciliation in a patient with chronic kidney disease. The patient has CKD stage 3 (elevated creatinine 1.6 mg/dL) and is taking both naproxen regularly and ibuprofen intermittently, representing dangerous NSAID duplication that significantly increases risk of acute kidney injury. Naproxen plus ibuprofen causing additive NSAID toxicity and increased kidney injury risk (option B) is the most concerning interaction because dual NSAID use provides no additional benefit but dramatically increases risk of renal vasoconstriction, acute kidney injury, GI bleeding, and cardiovascular events, especially dangerous in a patient with pre-existing CKD. Lisinopril plus chlorthalidone (option A) does not cause hyperkalemia - thiazide diuretics cause hypokalemia. Multivitamin plus chlorthalidone (option C) does not cause hypoglycemia. Lisinopril plus multivitamin (option D) does not cause hepatotoxicity. During medication reconciliation for CKD patients, identifying all NSAID use (prescription and OTC) is critical as these agents are contraindicated in advanced CKD and should be used cautiously if at all in earlier stages - acetaminophen or non-pharmacologic approaches are preferred for pain management.