HYGROTON
Clinical safety rating: caution
Comprehensive clinical and safety monograph for HYGROTON (HYGROTON).
Inhibits sodium reabsorption in the distal convoluted tubule by binding to the thiazide-sensitive sodium-chloride cotransporter (NCC), leading to increased excretion of sodium, chloride, and water.
| Metabolism | Primarily metabolized in the liver via CYP450 enzymes; metabolites are excreted renally. |
| Excretion | Renal (approximately 50-60% as unchanged drug and metabolites); biliary/fecal elimination accounts for a minor fraction, less than 10%. |
| Half-life | Terminal elimination half-life is approximately 40-50 hours, extending up to 70 hours in patients with renal impairment, allowing for once-daily dosing. |
| Protein binding | 75-95% bound to plasma proteins, primarily albumin and erythrocyte carbonic anhydrase. |
| Volume of Distribution | Approximately 3-4 L/kg (3.0-4.0 L/kg), indicating extensive tissue distribution and binding to erythrocytes. |
| Bioavailability | Oral: Approximately 65-70% due to incomplete absorption; no parenteral formulation available. |
| Onset of Action | Oral: 2 hours for initial diuresis; peak antihypertensive effect may require 2-4 weeks. |
| Duration of Action | Diuretic effect persists for 24-48 hours; antihypertensive effect lasts for up to 24 hours with once-daily dosing. |
| Molecular Weight | 338.77 |
25-50 mg orally once daily; may increase to 100 mg once daily for resistant hypertension or edema. Maximum dose 100 mg/day.
| Dosage form | TABLET |
| Renal impairment | GFR 15-29 mL/min: 25 mg every 48 hours; GFR <15 mL/min: avoid use (ineffective); GFR 30-59 mL/min: 25 mg once daily; GFR ≥60 mL/min: no adjustment. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 50%; Child-Pugh C: avoid use due to risk of electrolyte imbalance and encephalopathy. |
| Pediatric use | Infants and children: 0.5-1 mg/kg/dose orally once daily; maximum 50 mg/day. |
| Geriatric use | Start at 12.5-25 mg orally once daily; monitor renal function and electrolytes closely; avoid doses >50 mg/day due to increased risk of hyponatremia and hypokalemia. |
| 1st trimester | Avoid if possible; associated with neural tube defects and cardiovascular anomalies. Use only if benefit outweighs risk. |
| 2nd trimester | Avoid; may cause fetal electrolyte disturbances and placental hypoperfusion. |
| 3rd trimester | Avoid; risk of neonatal thrombocytopenia, electrolyte imbalances, and hypotension. |
Clinical note
Comprehensive clinical and safety monograph for HYGROTON (HYGROTON).
| Placental transfer | Crosses placenta; achieves fetal serum concentrations approximately 15% of maternal levels. |
| Breastfeeding | Hygroton (chlorthalidone) is excreted into breast milk in low amounts. Monitor infant for electrolyte disturbances and diuretic effects. Use caution, especially in neonates or infants with fluid/electrolyte imbalance. |
■ FDA Black Box Warning
No boxed warning.
| Serious Effects |
AnuriaSevere renal impairment (CrCl <30 mL/min)Sulfonamide allergyHypersensitivity to thiazide diureticsHepatic coma or precoma
| Precautions | Electrolyte disturbances: hypokalemia, hyponatremia, hypomagnesemia, Hyperuricemia and gout, Hyperglycemia, Orthostatic hypotension, Sulfonamide hypersensitivity cross-reactivity, Impaired renal function |
| Food/Dietary | Avoid excessive sodium intake as it may reduce antihypertensive efficacy. Potassium-rich foods (bananas, oranges, spinach) are not contraindicated but monitor potassium levels if used with ACE inhibitors or ARBs. Alcohol may potentiate orthostatic hypotension. |
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| Lactation Rating |
| L3 (Moderately Safe) |
| Teratogenic Risk | Chlorthalidone (Hygroton) is a thiazide-like diuretic classified as FDA Pregnancy Category B. Data from controlled studies in pregnant women are insufficient; however, thiazides cross the placenta and may cause fetal or neonatal effects such as jaundice, electrolyte disturbances, and thrombocytopenia. Use in the first trimester is not associated with major malformations, but second and third trimester exposure may lead to adverse fetal/neonatal effects. Avoid for treatment of gestational hypertension due to decreased maternal plasma volume and potential for placental hypoperfusion. Risk summary: Minimal teratogenic risk in first trimester, but caution in second and third trimester. |
| Fetal Monitoring | Monitor maternal blood pressure, serum electrolytes (especially potassium, sodium, chloride), renal function, and uric acid. In pregnancy, monitor fetal growth and amniotic fluid volume via ultrasound due to potential for placental hypoperfusion. Assess for signs of neonatal jaundice, thrombocytopenia, and electrolyte disturbances after delivery. |
| Fertility Effects | No known significant impact on fertility. Thiazide diuretics may cause minor changes in menstrual cycle but no established effect on conception or reproductive function. |
| Clinical Pearls |
| Hygroton (chlorthalidone) is a thiazide-like diuretic used primarily for hypertension and edema. Its long half-life (40-60 hours) allows once-daily dosing but increases risk of electrolyte disturbances, especially hypokalemia and hyponatremia. Monitor serum potassium and magnesium; consider potassium-sparing diuretic or supplementation. Effective in reducing cardiovascular events in hypertension, particularly in elderly patients. Can exacerbate gout by increasing serum uric acid. Onset of action is 2-3 hours, peak at 4-6 hours, duration up to 72 hours. |
| Patient Advice | Take in the morning to avoid nighttime urination. · Avoid excessive intake of salt substitutes high in potassium unless directed. · Report symptoms of electrolyte imbalance: muscle cramps, weakness, irregular heartbeat, excessive thirst, confusion. · May increase blood sugar; monitor glucose if diabetic. · Avoid dehydration; drink adequate fluids unless fluid restricted. · Use caution in hot weather or during exercise; risk of dehydration and electrolyte loss. · Do not stop abruptly without medical advice; may cause rebound hypertension. |