Haemodynamic and endocrine effects of digitoxin in healthy volunteers

A study was conducted to evaluate the effects of a single oral dose of digitoxin on the circulatory function and the renin-angiotensin-aldosterone system. Seven doses of digitoxin and 6 of a placebo were given at random to 13 healthy volunteers, all of whom remained at rest, without smoking, throughout the study. Blood samples were taken initially after 1 h at rest, and at 1, 2 and 24 h after receiving the dose. Concentrations of serum digitoxin, aldosterone, angiotensin II (A II) as well as plasma renin activity (PRA) were determined by radioimmunoassay (RIA). In all subjects the blood pressure did not change throughout the study. Digitoxin decreased the heart rate significantly during the first and second hours, while in the placebo group the heart rate remained unchanged during the same period. The placebo had no detectable effect on PRA, A II and aldosterone. Digitoxin decreased PRA and A II levels, reaching its maximum effect 2 h after the administration. There was no correlation between the serum digitoxin concentration and PRA, A II or the aldosterone values. Digitoxin reached its maximum effect upon these parameters faster than what is generally accepted.