The adequacy of laboratory monitoring in patients treated with spironolactone for congestive heart failure

OBJECTIVES This study was designed to determine the adequacy of monitoring patients receiving spironolactone as well as spironolactone's relationship to hyperkalemia. BACKGROUND After the Randomized Aldactone Evaluation Study (RALES) demonstrated a 30% mortality benefit for treating severe heart failure patients with spironolactone, acceptance of this drug was overwhelming. Hyperkalemia and worsening renal function were rare in RALES, but laboratory monitoring was frequent. In clinical practice, the incidence of hyperkalemia and worsening renal function and adequacy of follow-up is unknown. METHODS We reviewed the monitoring of congestive heart failure (CHF) patients with spironolactone initiation after publication of RALES. All potassium and creatinine determinations at baseline and within three months following therapy initiation were assessed. Increased potassium was defined as any [K] >= 5.5 mEq/l and severe hyperkalemia as any [K] >= 6.0. RESULTS A total of 840 patients had new prescriptions for spironolactone. Of these, 91% had baseline laboratory values, and 34% did not have any serum potassium or creatinine determined within three months. Patients seen in the cardiology clinic were more likely to have appropriate follow-up (p <= 0.001). Of 551 patients with follow-up laboratory values determined, 15% developed hyperkalemia and 6% developed severe hyperkalemia. Fifty-one patients (9%) developed renal dysfunction, of whom 25 developed hyperkalemia within three months. Hyperkalemia developed in 48 of 138 (35%) patients with baseline creatinine >= 1.5 mg/dl and 12 of 19 (63%) with baseline creatinine >= 2.5 mg/dl. CONCLUSIONS Many patients treated with spironolactone for CHF do not receive needed follow-up of potassium or creatinine concentrations, although hyperkalemia and renal dysfunction are common. Elevated baseline creatinine predicts patients at high risk. Physician education of the risks of spironolactone and the need for follow-up is essential.