DOCITEREN

Propranolol is a competitive antagonist at both beta, and beta₂-adrenoceptor, but has membrane stabilising activity at concentrations exceeding 1-3mg/litre, though such concentrations are rarely achieved during oral therapy. Competitive beta-blockade has been demonstrated in man by a parallel shift to the right in the dose-heart rate response curve to beta-agonists such as isoprenaline.

Triamterene is a potassium-sparing agent. Triamterene inhibits the reabsorption of sodium ions in exchange for potassium and hydrogen ions at that segment of the distal tubule under the control of adrenal mineralocorticoids (especially aldosterone). The fraction of filtered sodium reaching this distal tubular exchange site is relatively small, and the amount which is exchanged depends on the level of mineralocorticoid activity. Thus, the degree of natriuresis and diuresis produced by inhibition of the exchange mechanism is necessarily limited.

Hydrochlorothiazide is a diuretic with antihypertensive properties. It acts by inhibiting the renal tubular re-absorption of sodium and chloride ions, which are excreted with an accompanying volume of water. Potassium excretion is also promoted.