Most of the research supporting the use of thiazide diuretics in hypertension was done using chlortalidone, a different medication in the same class. Hydrochlorothiazide is less effective than chlortalidone for lowering blood pressure but the two medications have similar effects on lowering potassium. The thiazide-type diuretics (including hydrochlorothiazide) are less effective than the thiazide-like diuretics (chlortalidone and indapamide) for reducing the risk of heart attack, stroke, and heart failure in persons with high blood pressure and the thiazide-like and thiazide-type diuretics have similar rates of adverse effects.
Hydrochlorothiazide is also sometimes used to prevent osteopenia and for treatment of hypoparathyroidism,hypercalciuria, Dent's disease, and Ménière's disease. For diabetes insipidus, the effect of thiazide diuretics is presumably mediated by a hypovolemia-induced increase in proximal sodium and water reabsorption, thereby diminishing water delivery to the ADH-sensitive sites in the collecting tubules and increasing the urine osmolality.
Thiazides are also used in the treatment of osteoporosis. Thiazides decrease mineral bone loss by promoting calcium retention in the kidney, and by directly stimulating osteoblast differentiation and bone mineral formation.
It may be given together with other antihypertensive agents in fixed-dose combination preparations, such as in losartan/hydrochlorothiazide (see below).
Hyperuricemia (high levels of uric acid in the blood). All thiazide diuretics including hydrochlorothiazide can inhibit excretion of uric acid by the kidneys, thereby increasing serum concentrations of uric acid. This may increase the chance of gout.
These side effects increase with the dose of the medication and are most common at doses of greater than 25 mg per day.
Package inserts, based on case reports and observational studies, have reported that an allergy to a sulfa drug predisposes the patient to cross sensitivity to a thiazide diuretic. A 2005 review of the literature did not find support for this cross-sensitivity.
Mechanism of action
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. The major site of action in the nephron appears on an electroneutral NaCl co-transporter by competing for the chloride site on the transporter. By impairing Na+ transport in the distal convoluted tubule, hydrochlorothiazide induces a natriuresis and concomitant water loss. Thiazides increase the reabsorption of calcium in this segment in a manner unrelated to sodium transport. Additionally, by other mechanisms, HCTZ is believed to lower peripheral vascular resistance.
Hydrochlorothiazide is available as a generic drug under a large number of brand names, including Apo-Hydro, Aquazide, BPZide, Dichlotride, Esidrex, Hydrochlorot, Hydrodiuril, HydroSaluric, Hypothiazid, Microzide, Oretic and many others.
To reduce pill burden and in order to reduce side effects, hydrochlorothiazide is often used in fixed-dose combinations with many other classes of antihypertensive drugs such as:
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^Olde Engberink RH, Frenkel WJ, van den Bogaard B, Brewster LM, Vogt L, van den Born BJ (May 2015). "Effects of thiazide-type and thiazide-like diuretics on cardiovascular events and mortality: systematic review and meta-analysis". Hypertension. 65 (5): 1033–40. doi:10.1161/HYPERTENSIONAHA.114.05122. PMID25733241.