A 70-year-old man with a history of osteoarthritis has been taking Ibuprofen 600 mg three times daily for chronic knee pain. During a routine check-up, his blood pressure is found to be elevated at 160/95 mmHg, up from his usual 135/85 mmHg. Laboratory tests reveal an elevation in his kidney function tests and serum potassium level. Which of the following adverse effects of NSAIDS best explains these findings?

A. Cardiotoxicity: While NSAIDs can contribute to cardiovascular risks such as hypertension and fluid retention, nephrotoxicity is the more direct explanation for the elevated kidney function tests and potassium level. Cardiotoxicity typically presents with symptoms like heart failure or arrhythmias rather than kidney-related lab abnormalities. B. Nephrotoxicity: NSAIDs inhibit prostaglandin synthesis, which plays a key role in maintaining renal blood flow, especially in older adults or those with preexisting renal impairment. Chronic NSAID use can reduce glomerular filtration, leading to elevated creatinine, hyperkalemia, and worsening blood pressure control, all of which are evident in this patient. C. Neurotoxicity: Neurotoxic effects are not commonly associated with NSAID use. Symptoms of neurotoxicity include confusion or seizures, which are not relevant to the clinical findings in this scenario. D. Hepatotoxicity: NSAID-induced liver injury is rare and would typically present with elevated liver enzymes (AST, ALT), not elevated creatinine or potassium. The current lab findings and blood pressure changes are more consistent with kidney involvement.