Pharmacokinetic and pharmacodynamic interaction of single oral doses of valsartan and furosemide

Abstract

Objective: Pharmacokinetic and pharmacodynamic interactions between single oral doses of valsartan (160 mg) and furosemide (40 mg) were investigated in an open, randomized, three-period crossover study in twelve healthy male subjects.

Methods: A washout period of one week was observed between treatments. Pharmacokinetic measurements included plasma concentrations of valsartan and furosemide, and urinary excretion of the latter. Plasma renin activity (PRA), plasma angiotensin II, blood pressure, heart rate, as well as urinary water and electrolyte excretion were determined as pharmacodynamic variables. Efficiency of furosemide for sodium and water excretion was calculated as the ratio of the measured pharmacodynamic effect and the urinary excretion of furosemide.

Results: Simultaneous administration of valsartan and furosemide did not modify the pharmacokinetics of valsartan. In contrast, C_max, AUC, and urinary excretion of furosemide were significantly reduced following simultaneous treatment with valsartan. Inter- and intra-individual variability of the pharmacokinetic variables was high for both furosemide and valsartan.

PRA and angiotensin II increased, and blood pressure decreased after all treatments. These effects were most pronounced after the combined treatment. The decrease in blood pressure was additive, at most, while the increase in PRA and angiotensin II appeared to exceed simple addition. No relevant effects on heart rate were observed. The diuretic effect of furosemide, as assessed by urinary water and electrolyte excretion, was unchanged after co-administration of valsartan, despite the lower bioavailability of furosemide after the combined treatment.