Torasemide significantly reduces thiazide-induced potassium and magnesium loss despite supra-additive natriuresis.

BACKGROUND: Resistance to high-dose loop diuretics can be overcome either by co-administration with thiazides or by treatment with medium-dose loop diuretics combined with thiazides. Combination therapy has been proven to be superior to high-dose loop diuretic monotherapy for cardiac and renal edema. However, such a strongly efficacious short-term regimen is often complicated by undesired effects, including circulatory collapse and electrolyte disturbances. The question of whether the loop diuretic/thiazide combinations are efficacious and safe when conventional doses are combined has not yet been answered.

METHODS: The effects of hydrochlorothiazide (HCT) and torasemide (TO) given alone on the excretion of Na+, Cl-, K+, Mg2+, and Ca2+ were compared with the effects of combined administration of the diuretics in 12 healthy volunteers.

RESULTS: The co-administration of HCT (25 mg) with TO (5 or 10 mg) strongly increased Na+ excretion. However, the combination significantly reduced K+ and Mg2+ excretion. The K+-sparing effect of the HCT/TO combination was shown to be due to a significant reduction in the HCT-induced increase in fractional K+ excretion by the loop diuretic. Total excretion of Ca2+ relative to Na+ excretion was less with the HCT/TO combination than with TO given alone.

CONCLUSION: The enhancement of desired NaCl excretion by the HCT/TO combination with significant reduction of undesired loss of K+ and Mg2+ meets clinical requirements but has to be validated in long-term clinical trials.