CAPOZIDE (captopril and hydrochlorothiazide tablets, USP) for oral administration combines two antihypertensive agents: captopril and hydrochlorothiazide. The mechanism of action of captopril has not yet been fully elucidated. Captopril prevents the conversion of angiotensin I to angiotensin II by inhibition of ACE, a peptidyldipeptide carboxy hydrolase. Hydrochlorothiazide belongs to thiazide class of diuretics. It reduces blood volume by acting on the kidneys to reduce sodium (Na+) reabsorption in the distal convoluted tubule. CAPOZIDE (captopril and hydrochlorothiazide tablets, USP) is indicated for the treatment of hypertension. The blood pressure lowering effects of captopril and thiazides are approximately additive. Major side effects are: Black, tarry stools; chest pain; chills; cough; fever; painful or difficult urination; shortness of breath; sore throat; sores, ulcers, or white spots on lips or in mouth; swollen glands; unusual bleeding or bruising; unusual tiredness or weakness. It has been reported that indomethacin may reduce the antihypertensive effect of captopril, especially in cases of low renin hypertension. Captopril’s effect will be augmented by antihypertensive agents that cause renin release. For example, diuretics (e.g., thiazides) may activate the renin-angiotensin-aldosterone system.

Like other thiazides, chlorothiazide promotes water loss from the body (diuretics). It inhibits Na+/Cl- reabsorption from the distal convoluted tubules in the kidneys. Thiazides also cause loss of potassium and an increase in serum uric acid. Thiazides are often used to treat hypertension, but their hypotensive effects are not necessarily due to their diuretic activity. Thiazides have been shown to prevent hypertension-related morbidity and mortality although the mechanism is not fully understood. Thiazides cause vasodilation by activating calcium-activated potassium channels (large conductance) in vascular smooth muscles and inhibiting various carbonic anhydrases in vascular tissue. Chlorothiazide affects the distal renal tubular mechanism of electrolyte reabsorption. At maximal therapeutic dosages, all thiazides are approximately equal in their diuretic efficacy. Chlorothiazide increases excretion of sodium and chloride in approximately equivalent amounts. Natriuresis may be accompanied by some loss of potassium and bicarbonate. After oral doses, 10-15 percent of the dose is excreted unchanged in the urine. Chlorothiazide crosses the placental but not the blood-brain barrier and is excreted in breast milk. As a diuretic, chlorothiazide inhibits active chloride reabsorption at the early distal tubule via the Na-Cl cotransporter, resulting in an increase in the excretion of sodium, chloride, and water. Thiazides like chlorothiazide also inhibit sodium ion transport across the renal tubular epithelium through binding to the thiazide sensitive sodium-chloride transporter. This results in an increase in potassium excretion via the sodium-potassium exchange mechanism. The antihypertensive mechanism of chlorothiazide is less well understood although it may be mediated through its action on carbonic anhydrases in the smooth muscle or through its action on the large-conductance calcium-activated potassium (KCa) channel, also found in the smooth muscle. It is marketed under the brand name Diuril.