Pharmacokinetics: 

Thiazides are moderately potent diuretics and exert their diuretic effect by reducing the reabsorption of electrolytes from the renal tubules, thereby increasing the excretion of sodium and chloride ions, and consequently of water. They act mainly at the beginning of the distal tubules. The excretion of other electrolytes, notably potassium and magnesium, is also increased. The excretion of calcium is reduced. They also reduce carbonic-anhydrase activity so that bicarbonate excretion is increased, but this effect is generally small compared with the effect on chloride excretion and does not appreciably alter the pH of the urine. They may also reduce the glomerular filtration rate. Their hypotensive effect is probably partly due to a reduction in peripheral resistance; they also enhance the effects of other antihypertensives.

Hydrochlorothiazide is a diuretic and antihypertensive. It is the 3,4-dihydro derivative of chlorothiazide. Its chemical name is 6-chloro-3,4-dihydro-2H-1,2,4 benzothiadiazine-7-sulfonamide 1,1 dioxide. Its empirical formula is C7H8CIN304S2. Hydrochlorothiazide is fairly rapidly absorbed from the gastrointestinal tract. It is reported to have a bioavailability of about 65% to 70%. It has been estimated to have a plasma half-life of between about 5 and 15 hours and appears to be preferentially bound to red blood cells. It is excreted mainly unchanged in the urine. Hydrochlorothiazide crosses the placental barrier and is distributed into breast milk.

Indications:

Hydrochlorothiazide is used in the treatment of edema associated with heart failure and with renal and hepatic disorders. It is also used in the treatment of hypertension, either alone or together with other antihypertensives such as ACE inhibitors and beta blockers.

Hydrochlorothiazide is also indicated in the treatment of edema accompanying premenstrual syndrome, prevention of water retention associated with corticosteroids and estrogens, treatment of diabetes insipidus, and prevention of renal calculus formation in patients with hypercalciuria.