Thiazide diuretics · Cardiovascular
Hydrochlorothiazide
HCTZ
The thiazide: modest diuresis, durable blood-pressure effect, and a fistful of electrolyte homework.
Mechanism
Inhibits the Na-Cl cotransporter in the distal convoluted tubule; chronic BP effect is mostly vascular, not volume.
Indications
- Hypertension
- Recurrent calcium kidney stones (reduces urinary calcium)
Formulations
Dosing concepts
Efficacy floor
Loses diuretic potency at low GFR (roughly <30), where loops take over for volume, though some BP effect persists.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~70%
- Half-life
- ~6-15 h
- Elimination
- renal
Adverse effects
- Hyponatremia (especially older women)common & serious
- Hypokalemiacommon
- Hyperuricemia and goutcommon
- Hyperglycemia, mildcommon
- Photosensitivitycommon
Contraindications & precautions
Contraindications
- Anuria
- Severe sulfonamide hypersensitivity (documented cross-reaction)
Precautions
- Gout history
- Diabetes
- Lithium therapy
Interactions
Monitoring
Sodium and potassium
The two classic thiazide casualties · Within 2-4 weeks of starting, then periodically
Blood pressure
Effectiveness
Uric acid if gout history
Precipitates flares
Counselling points
- Morning dosing keeps the (mild) diuresis out of your night.
- Use sun protection; this drug can make skin burn faster.
Clinical pearls
- The confused older adult started on a thiazide two weeks ago has hyponatremia until proven otherwise.
References & review
- Hydrochlorothiazide product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-15 · jurisdiction: global · drug information changes; verify against current references before practice use.