Medical Author: Omudhome Ogbru, Pharm.D.
Medical Editor: Jay Marks, M.D.

GENERIC NAME: hydrochlorothiazide

BRAND NAMES: Hydrodiuril, Ezide, Hydro-Par, Microzide, and many combinations with other drugs

DRUG CLASS AND MECHANISM: Hydrochlorothiazide is a diuretic (water pill) used for treating high blood pressure (hypertension) and accumulation of fluid. It works by blocking salt and fluid reabsorption in the kidneys, causing increased urine output (diuresis). The mechanism of its action in lowering high blood pressure is not well understood.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes

PREPARATIONS: Tablets: 12.5, 25, 50, and 100 mg; Capsules: 12.5 mg

STORAGE: Hydrochlorothiazide should be stored at room temperature, 15 to 30 C (59 to 86 F), in a tight, light-resistant container.

PRESCRIBED FOR: Hydrochlorothiazide is used to treat excessive fluid accumulation and swelling (edema) of the body caused by heart failure, cirrhosis, chronic kidney failure, corticosteroid medications, and nephrotic syndrome. It also is used alone or in conjunction with other blood pressure lowering medications to treat high blood pressure. Although hydrochlorothiazide is approved for treating edema in cirrhosis of the liver, it is rarely used because of the availability of more potent diuretics that are more effective. Hydrochlorothiazide can be used to treat calcium-containing kidney stones because it decreases the amount of calcium excreted by the kidneys in the urine and thus decreases the amount of calcium in urine to form stones.

DOSING: Hydrochlorothiazide may be taken with or without food. The usual adult dose for hypertension is 12.5 to 50 mg once daily. The usual adult dose for treating edema is 25-100 mg once daily or in divided doses.

DRUG INTERACTIONS: Hydrochlorothiazide reduces the elimination of lithium (Lithobid) by the kidneys and can lead to lithium toxicity. Nonsteroidal antiinflammatory drugs, for example, ibuprofen, may reduce the blood pressure effects of hydrochlorothiazide.

Blood sugar levels can be elevated by hydrochlorothiazide, necessitating adjustment in the doses of medications that are used for treating diabetes.

Combining hydrochlorothiazide with corticosteroids may increase the risk for low levels of blood potassium and other electrolytes. Low blood potassium can increase the toxicity of digoxin (Lanoxin). Cholestyramine (Questran, Questran Light) and colestipol (Colestid) bind to hydrochlorothiazide and reduce its absorption from the gastrointestinal tract by 43%-85%.

PREGNANCY: There are no adequate studies of hydrochlorothiazide in pregnant women.

NURSING MOTHERS: Hydrochlorothiazide is excreted in breast milk. There is some evidence that it may reduce production of breast milk.

SIDE EFFECTS: Side effects of hydrochlorothiazide include weakness, low blood pressure, light sensitivity (rash caused by sunlight), impotence, nausea, abdominal pain, electrolyte disturbances, pancreatitis, jaundice, anaphylaxis, and rashes, both mild and severe. Patients allergic to sulfa may also be allergic to hydrochlorothiazide because of the similarity in the chemical structure of the medications.

Hydrochlorothiazide can aggravate kidney dysfunction and is used with caution in patients with kidney disease. Hydrochlorothiazide can lower blood potassium, sodium, and magnesium levels. Low potassium and magnesium levels can lead to abnormalities in heart rhythm, especially in patients already taking digoxin (Lanoxin). During hydrochlorothiazide treatment, supplementation with potassium is common to prevent low potassium levels.

Blood uric acid levels can increase during hydrochlorothiazide treatment, and this elevation may cause an episode of acute gout in some individuals.

Thiazide diuretics may increase blood sugar (glucose) levels and precipitate latent diabetes.

Reference: FDA Prescribing Information