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Hydrochlorothiazide – Uses, Dosage & Side Effects

Hydrochlorothiazide is a thiazide diuretic used to treat high blood pressure and fluid retention. It works by increasing the amount of water and salt the kidneys remove from the blood.

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Things worth knowing about "Hydrochlorothiazide"

Hydrochlorothiazide is a thiazide diuretic used to treat high blood pressure and fluid retention. It works by increasing the amount of water and salt the kidneys remove from the blood.

What is Hydrochlorothiazide?

Hydrochlorothiazide (commonly abbreviated as HCT or HCTZ) is a medication belonging to the class of thiazide diuretics, often referred to as water pills. It is one of the most widely prescribed antihypertensive agents worldwide and has been used in clinical practice since the 1950s. Hydrochlorothiazide is available by prescription only and is frequently used in combination with other blood pressure-lowering medications.

Indications

Hydrochlorothiazide is indicated for the following conditions:

Arterial hypertension (high blood pressure) – as monotherapy or in combination
Edema (fluid retention) associated with heart failure, liver disease, or kidney disease
Nephrogenic diabetes insipidus – paradoxically used to reduce urine output
Prevention of kidney stones in patients with excessive calcium excretion in the urine (hypercalciuria)

Mechanism of Action

Hydrochlorothiazide works by selectively inhibiting the sodium-chloride cotransporter (NCC) in the distal convoluted tubule of the kidney. This prevents reabsorption of sodium and chloride from the filtrate back into the bloodstream. As a result, more water is excreted in the urine, leading to a reduction in blood volume and blood pressure. Hydrochlorothiazide also has a mild direct vasodilatory effect on blood vessels, which further contributes to lowering blood pressure.

Dosage

The dosage of hydrochlorothiazide depends on the condition being treated and the individual patient. General guidelines include:

High blood pressure: 12.5 to 25 mg once daily, typically in the morning
Edema: 25 to 100 mg daily, depending on severity
Administration is recommended in the morning to minimize nighttime urination.
The exact dose should always be determined by the prescribing physician.

Side Effects

Like all medications, hydrochlorothiazide may cause side effects. Common and clinically important side effects include:

Electrolyte disturbances: low potassium (hypokalemia), low sodium (hyponatremia), low magnesium
Elevated uric acid levels, which may trigger gout attacks
Elevated blood glucose levels – particularly relevant for patients with diabetes
Increased blood lipid levels (cholesterol and triglycerides)
Dizziness and low blood pressure upon standing (orthostatic hypotension)
Increased skin sensitivity to sunlight (photosensitivity) – use of sun protection is advised
Rarely: allergic reactions, pancreatitis, impaired kidney function

Drug Interactions

Hydrochlorothiazide can interact with several other medications and substances:

ACE inhibitors and ARBs (sartans): Enhanced blood pressure-lowering effect – often desirable in combination products
Lithium: Increased lithium plasma levels possible – close monitoring required
NSAIDs (e.g., ibuprofen): May reduce the diuretic and antihypertensive effects
Antidiabetic drugs: Efficacy may be reduced due to elevated blood sugar
Digitalis glycosides: Hypokalemia caused by HCTZ increases the risk of cardiac arrhythmias

Contraindications

Hydrochlorothiazide should not be used in patients with:

Severe renal impairment (anuria)
Severe hepatic impairment
Uncontrolled hypokalemia or hyponatremia
Known hypersensitivity to sulfonamides or hydrochlorothiazide itself
Pregnancy (especially the 2nd and 3rd trimester) and breastfeeding

Treatment Context

Hydrochlorothiazide is frequently used not as a standalone treatment but as part of fixed-dose combination products with other antihypertensives – for example, with ACE inhibitors (e.g., ramipril/HCT), ARBs (e.g., valsartan/HCT), or beta-blockers. These combinations improve blood pressure control and may help minimize side effects. Regular monitoring of blood pressure and laboratory values (electrolytes, kidney function, blood glucose) is recommended throughout treatment.

References

Williams B et al. – 2018 ESC/ESH Guidelines for the management of arterial hypertension. European Heart Journal, 2018; 39(33): 3021–3104.
Whelton PK et al. – 2017 ACC/AHA High Blood Pressure Guideline. Journal of the American College of Cardiology, 2018; 71(19): e127–e248.
Brunton LL, Knollmann BC (eds.) – Goodman & Gilman's The Pharmacological Basis of Therapeutics, 13th edition. McGraw-Hill, 2018.

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