Relative potency of spironolactone, triamterene and potassium chloride in thiazide-induced hypokalaemia.

1 The influence of spironolactone 50 mg and 100 mg daily, triamterene 100 mg and 200 mg daily, potassium chloride 32 mmol and 64 mmol daily and placebo on plasma potassium and other variables was examined in a random crossover study of nine hypertensive patients taking bendrofluazide 10 mg daily. 2 Spironolactone and triamterene had significant and parallel dose-response curves for plasma potassium, with a relative potency for triamterene:spironolactone of 0.25:1, significantly lower than the accepted 0.5:1 ratio. These drugs also lowered serum sodium, bicarbonate and body weight, and increased serum urea and creatinine. 3 Potassium chloride increased plasma potassium above placebo values, but the dose-response was not significant and was not parallel with those of the potassium-sparing drugs. Seven of nine patients remained hypokalaemic despite treatment with 64 mmol potassium chloride daily. 4 The relative expense, convenience and toxicity of the potassium-sparing drugs should be assessed at equivalent doses, namely spironolactone 50 mg:triamterene 200 mg:amiloride 20 mg. Potassium chloride does not correct moderate diuretic-induced hypokalaemia even at doses of 64 mmol daily.