List of Diuretic Agents | Veterinary Pharmacology

Here is a list of four diuretic agents.

These drugs are good antihypertensive agents used either alone or in combination with other drug. Where a combined therapy is necessary, a diuretic drug is preferably used along with any other drug because these drugs potentiate the effect of other antihypertensive drugs.

Though the exact mechanism of their antihypertensive action is not yet clearly known, there seems to have three main processes:

(i) By decreasing interstitial fluid volume,

(ii) By reducing Na⁺ concentration in vascular smooth muscle which may secondarily reduce intracellular Ca²⁺ concentration, and

(iii) By decreasing the affinity and response of cell surface receptors to vasoconstrictor hormones.

1. Thiazide Diuretics (Benzothiadiazides):

They are most commonly used. They mainly inhibit the Na⁺ – Cl^– cotransport process in the distal convoluted tubule of nephron resulting in increased renal excre­tion of Na⁺ and Cl^–ions. Thiazides also inhibit Na⁺ reabsorption per se and function of carbonic anhydrase enzyme to enhance excretion of Na⁺ and HCO₃^–. They also increase excretion of K⁺.

2. High-Ceiling (Loop) Diuretics:

They are weak antihypertensive agents, though their diuretic efficacy is greater than the thiazides. The advantage of using these drugs is that they are effective even in renal failure patient. They inhibit Na⁺ – K⁺ – 2Cl^– co-transport mechanism in the ascending limb of Henle’s Loop, and thereby increase the excretion of these electro­lytes. Higher doses of these drugs promote uric acid excretion.

3. K⁺ Sparing Diuretics:

Spironolactone, triamterene and amiloride are the drugs under this group. Spironolactone is a competitive inhibitor of aldosterone. The normal function of aldosterone is to increase the reabsorption of Na⁺& excretion of K⁺.

Spironolactone reverses this process by inhibiting the function of aldosterone. It is contraindicated in acute renal failure and hyperkalemia. Triamterene and amiloride mainly inhibit ‘Na⁺ reabsorption per se’ through the late distal tubule and collecting duct. Their action does not depend on the function of aldosterone.

4. β-Adrenergic Antagonists:

These are very important antihypertensive agents. All of them are equally effec­tive though their mechanisms of action may vary. The exact mechanism of their antihypertensive effect is not yet known. It seems that a multiple modes of action helps in reducing the blood pressure. The first and foremost one of them is seemed to be inhibition of renin secretion from kidney.

Others are decrease in cardiac output, alteration of adrenergic neuronal function, prostaglandin synthesis, baroreceptor sen­sitivity and the control of blood pressure in the CNS.

They also have intrinsic sympathomimetic activity. Examples are propranolol, nadolol, timolol, pindolol, penbutolol, carteolol, labetalol, metoprolol, atenolol, acebutolol, etc. Labetalol addi­tionally blocks vascular postsynaptic a₁ adrenoceptors to further increase its hypoten­sive effect.