[Potassium metabolism during antihypertensive treatment with beta-receptor blocker and diuretic treatment]

In a controlled, prospective, cross-over study 15 patients with essential hypertension received for four weeks either a combination of beta-receptor blocker and diuretic (twice 10 mg pindolol and 5 mg clopamide daily) or of three drugs: beta-receptor blocker, diuretic and sodium-preserving diuretic (twice daily 10 mg timolol, 25 mg hydrochlorothiazide and 2.5 mg amiloride). Both drug combinations produced quantitatively comparable and definite blood pressure lowering from 162/102 mmHg to 128/82 and 130/82, or 130/84 and 127/82, respectively, after two and four weeks. A significant fall in serum potassium from 4.24 to 3.77 and 3.92 mmol/l occurred with the combined two drugs but not the combination of three. With the two-drug combination renal potassium excretion was significantly raised at one of two control points in time. Heart rate remained constant with the two-drug treatment but fell significantly on three-drug administration. There were more side effects with the two-drug preparation. Combinations of beta-receptor blockers and diuretics are thus by no means potassium neutral but can cause renal potassium loss, fall in serum potassium and hypokalaemia. For this reason combining potassium-sparing diuretic with beta-receptor blocker and diuretics is reasonable and justified.