HYDROCHLOROTHIAZIDE
Clinical safety rating: safe
Animal studies have demonstrated safety
Thiazide diuretic that inhibits the sodium-chloride symporter (NCC) in the distal convoluted tubule of the kidney, reducing reabsorption of sodium and chloride, leading to increased excretion of water and electrolytes.
| Metabolism | Not extensively metabolized; primarily excreted unchanged in urine. |
| Excretion | Primarily renal (≥95%) via glomerular filtration and tubular secretion, with approximately 60% of the dose excreted unchanged in urine. Minor biliary/fecal excretion accounts for <5%. |
| Half-life | Terminal elimination half-life is 5.6–14.8 hours (mean ~9 hours). In patients with renal impairment (CrCl <30 mL/min), half-life is prolonged up to 24–48 hours, necessitating dose adjustment. |
| Protein binding | Approximately 68% bound to plasma albumin (primarily) and alpha-1-acid glycoprotein. |
| Volume of Distribution | Volume of distribution is 3.6–9.0 L/kg (mean ~4.8 L/kg), indicating extensive distribution into extravascular tissues, including erythrocytes. |
| Bioavailability | Oral bioavailability is 60–70% (range 50–80%), with food slightly increasing absorption. |
| Onset of Action | Oral: diuresis begins within 2 hours; peak effect at 4–6 hours. |
| Duration of Action | Approximately 6–12 hours; antihypertensive effect may persist up to 24 hours, allowing once-daily dosing. |
| Molecular Weight | 297.74 |
Oral: 25-100 mg daily in 1-2 divided doses. Maximum dose 200 mg/day.
| Dosage form | CAPSULE |
| Renal impairment | GFR 30-50 mL/min: usual dose. GFR 15-29 mL/min: 12.5-25 mg once daily. GFR <15 mL/min: not recommended. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B: caution, reduce dose by 50%. Child-Pugh C: contraindicated. |
| Pediatric use | Oral: 2-3 mg/kg/day in 2 divided doses. Maximum: 100 mg/day. |
| Geriatric use | Start at 12.5-25 mg once daily; titrate slowly to avoid electrolyte disturbances and hypotension. |
| 1st trimester | Use only if potential benefit justifies risk. Associated with increased risk of neural tube defects and other congenital anomalies when used in first trimester. |
| 2nd trimester | Use with caution. May cause fetal or neonatal jaundice, electrolyte disturbances, and thrombocytopenia. |
| 3rd trimester | Avoid near term. Can cause fetal or neonatal electrolyte disturbances, hyperbilirubinemia, and thrombocytopenia. |
Clinical note
Other antihypertensive drugs can have additive effects Lithium levels may be increased Can cause hypokalemia and hyponatremia.
| Placental transfer | Crosses the placenta; detectable in fetal tissues and amniotic fluid. |
| Breastfeeding | Hydrochlorothiazide is excreted into breast milk in small amounts; use with caution in nursing mothers. Theoretical risk of electrolyte depletion and thrombocytopenia in the infant. |
■ FDA Black Box Warning
No FDA black box warning.
| Common Effects | Limited data available |
| Serious Effects |
AnuriaSulfonamide allergy (cross-sensitivity)Hypersensitivity to hydrochlorothiazide or other thiazide diuretics
| Precautions | Hypokalemia and hypomagnesemia may occur; monitor electrolytes., Hyperuricemia may precipitate gout., May cause hyperglycemia in diabetic patients., Photosensitivity reactions., May exacerbate systemic lupus erythematosus. |
| Food/Dietary | Avoid excessive intake of potassium-rich foods (bananas, oranges, tomatoes, spinach, potatoes) if taking potassium supplements or potassium-sparing diuretics, but generally not restricted unless hyperkalemia is a concern. Maintain adequate fluid intake to prevent dehydration. Limit sodium intake to enhance antihypertensive effect and reduce fluid retention. Do not use salt substitutes containing potassium without medical advice. Grapefruit juice has no significant interaction with HCTZ. Alcohol may potentiate orthostatic hypotension and diuretic effects. |
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| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | First trimester: Not associated with major malformations in human data; second/third trimester: Risk of fetal or neonatal adverse effects including electrolyte imbalance, jaundice, thrombocytopenia, and possible fetal/neonatal hypotension. Avoid for treatment of gestational hypertension as it reduces plasma volume and placental perfusion. |
| Fetal Monitoring | Monitor maternal electrolytes (especially potassium, sodium, magnesium, chloride), renal function, and blood pressure. Fetal monitoring for growth and amniotic fluid volume (oligohydramnios risk). Neonatal monitoring for jaundice, thrombocytopenia, and electrolyte imbalance. |
| Fertility Effects | No direct evidence of altered fertility in humans. Theoretical concerns due to electrolyte disturbances or volume depletion affecting reproductive function, but not well documented. |
| Clinical Pearls | Hydrochlorothiazide (HCTZ) is a thiazide diuretic primarily used for hypertension and edema. It inhibits the Na+/Cl- cotransporter in the distal convoluted tubule. Onset of diuresis occurs within 2 hours, peaks at 4-6 hours, and lasts about 6-12 hours. Monitor serum potassium, sodium, and magnesium; may cause hypokalemia, hyponatremia, and hypomagnesemia. Avoid in patients with anuria, sulfonamide allergy, or severe renal impairment (CrCl <30 mL/min). May exacerbate gout by reducing uric acid excretion; consider allopurinol prophylaxis. HCTZ increases lithium levels; monitor closely. In diabetes, may cause hyperglycemia. For hypertension, low doses (12.5-25 mg) are effective with less metabolic disturbance. Consider adding a potassium-sparing diuretic if hypokalemia occurs. Photosensitivity reactions possible; advise sun protection. |
| Patient Advice | Take this medication exactly as prescribed, usually once daily in the morning to avoid nighttime urination. · You may need to have regular blood tests to check your electrolyte levels and kidney function. · This medication can cause dizziness or lightheadedness; rise slowly from sitting or lying positions. · Avoid prolonged sun exposure and use sunscreen, as this drug can increase sensitivity to sunlight. · Do not stop taking this medication without consulting your doctor, even if you feel well. · Monitor your blood pressure regularly at home and keep a log to share with your healthcare provider. · Take this medication with food or milk if it causes stomach upset. · Report any signs of electrolyte imbalance: muscle cramps, weakness, irregular heartbeat, excessive thirst, or confusion. · If you have diabetes, monitor your blood sugar more frequently, as hydrochlorothiazide can raise glucose levels. · Avoid alcohol, which can increase the risk of dizziness and dehydration. · Do not take any other medications, including over-the-counter drugs, without consulting your doctor. · Inform all healthcare providers that you are taking this medication before any surgery or medical procedure. |