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Spironolactone reduces morbidity and mortality in patients with severe congestive heart failure and guidelines have recommended adding spironolactone to treatment with ACE inhibitors and β blockers. A prospective observational study in Copenhagen has highlighted the danger of renal impairment and of hyperkalaemia.
The study included 125 consecutive patients at an outpatient clinic for congestive heart failure. All patients had a left ventricular ejection fraction (LVEF) of 45% or less or were taking spironolactone. (Sixty patients were already taking spironolactone on entry to the 2 year study and 65 began spironolactone during the study.) Ninety three patients were receiving a potassium supplement at baseline. Supplementation was stopped in 66 patients and gradually reduced in the other 27. Mean peak serum concentrations of creatinine and potassium were 167.6 μmol/L and 5.0 mmol/L. Serum creatinine increased during the study by 20% in over a half (55%) of patients, by 50% in a quarter (24%) of patients, and by 100% in a tenth (9%). Seventy three patients (58%) had a serum creatinine of more than 130 μmol/L and 28 (18%) more than 220 μmol/L. Serum potassium concentrations of >5, >5.5, and >6 mmol/L occurred in 45 (36%), 21 (17%), and 13 (10%). The risk of a 50% or greater increase in serum creatinine increased by 74% for every 10 year increase in age and decreased by 6% for every 10% increase in LVEF. The risk of severe hyperkalaemia (serum potassium >6 mmol/L) increased 3.4 fold for each increase in New York Heart Association functional class and decreased by 63% for each 10% increase in LVEF.
Spironolactone may be associated with more frequent adverse effects than is generally realised. Doses of other diuretics may need to be reduced and frequent laboratory monitoring is essential.