A client's hypertension has not responded significantly to first-line therapies, so the primary health care provider has prescribed aliskiren and spironolactone. In addition to blood pressure monitoring. What assessment should the nurse prioritize?

A. AST, ALT, and bilirubin levels: While liver function should be monitored, it is not the immediate concern with aliskiren and spironolactone. These medications affect renal and electrolyte balance, so liver enzymes are less urgent to check. B. Serum potassium level: Spironolactone is a potassium-sparing diuretic, and hyperkalemia (elevated potassium) is a common side effect. Since aliskiren also impacts renal function, monitoring potassium is essential to avoid complications like arrhythmias. C. Quantity and character of urine output: Urine output is important to assess for renal issues, but the priority here is electrolyte imbalances, especially potassium. Monitoring output is secondary to potassium levels. D. Heart rhythm: While monitoring heart rhythm is crucial, particularly if hyperkalemia is suspected or confirmed, directly assessing the serum potassium level is a more proactive and specific way to identify the underlying cause and risk of these arrhythmias.