Hydrochlorothiazide
A thiazide diuretic used for high blood pressure and for edema from heart, liver or kidney disease.
Also called HCTZ (abbreviation).
Drug card
- Class
- Thiazide diuretic
- How it works
- Blocking salt reabsorption in the distal tubule, so more salt and water leave
- Used for
- High blood pressure
- Edema in heart failure, cirrhosis or kidney disease
- Known for
- Low potassium (hypokalemia)
- Raised uric acid (hyperuricemia)
- Higher risk of non-melanoma skin cancer
- Its name
- -thiazide, -tizide means a thiazide diuretic
Study it as a flashcard, and it comes back before you forget it.
Mechanism of action
How does hydrochlorothiazide work?
Hydrochlorothiazide, a benzothiadiazine sulfonamide, blocks sodium and chloride reabsorption in the distal tubule. It is not metabolized: at least 61% of a dose leaves unchanged in the urine within 24 hours, and its half-life is 5.6 to 14.8 hours. Diuresis starts within 2 hours and lasts 6 to 12 hours.
Like other thiazide and thiazide-like diuretics: They block the sodium-chloride cotransporter in the distal convoluted tubule, so more sodium, chloride and water leave in the urine, along with potassium and magnesium, while calcium and uric acid are held back. The lasting fall in blood pressure comes mainly from lower peripheral resistance, by a mechanism that is not fully understood.
Uses
What is hydrochlorothiazide used for?
- High blood pressure
- Edema in heart failure, cirrhosis or kidney disease
Side effects
Side effects of hydrochlorothiazide
- Low potassium (hypokalemia)Known forSerious
- Raised uric acid (hyperuricemia)Known for
- Higher risk of non-melanoma skin cancerKnown forSerious
- Low sodium (hyponatremia)Serious
- Gout attacks
- Raised blood sugar (hyperglycemia)
- Raised cholesterol and triglycerides
- Slightly raised calcium (hypercalcemia)
- Low magnesium (hypomagnesemia)
- Dizziness on standing (orthostatic hypotension)
- Sensitivity to sunlight (photosensitivity)
- Sudden myopia and angle-closure glaucoma (rare)Serious
Known for marks what an exam expects you to know it for.
Watch for
Cautions and what sets it apart
- Acute angle-closure glaucoma, often within weeks of starting, is treated by stopping it fast; sulfonamide or penicillin allergy adds risk.
- Lithium generally should not be combined with it, because of lithium toxicity.
- It is stopped before parathyroid tests: it raises calcium and can unmask hyperparathyroidism.
- Cholestyramine and colestipol bind it and cut its absorption.
Good to know: Its label also warns of non-melanoma skin cancer, mostly squamous cell carcinoma, seen mainly with large cumulative doses.
Remember it
A way to remember it
GLUC
- G
- Glucose up
- L
- Lipids up
- U
- Uric acid up
- C
- Calcium up
Think 'hyper-GLUC': thiazides raise blood glucose, lipids, uric acid and calcium, while potassium, sodium and magnesium fall.
A mnemonic widely used in teaching
Its name
-thiazide, -tizide means thiazide diuretic
Hydrochlorothiazide and bendroflumethiazide keep the older -thiazide spelling; WHO uses -tizide for newer names. Thiazide-like chlortalidone and indapamide don't carry it.
- Every drug name stem
Its class
Thiazide and thiazide-like diuretics
Other thiazide and thiazide-like diuretics with a card:
Easily mixed up with loop diuretics and mineralocorticoid receptor antagonists.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
For learning pharmacology, not for treatment decisions: no doses are given, and a prescriber, pharmacist or the product's own label is the word on any one patient. Spotted a mistake? Tell us and we'll correct it.
Blood pressure
Hydrochlorothiazide is one of 27 drugs practiced together here: their classes, how they work, what they treat and what they're known for.
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