CLORPRES
Clinical safety rating
cautionComprehensive clinical and safety monograph for CLORPRES (CLORPRES).
CLORPRES is a combination of clonidine (alpha-2 adrenergic agonist that reduces sympathetic outflow) and chlorthalidone (thiazide diuretic that inhibits sodium reabsorption in distal tubules).
| Metabolism | Clonidine: hepatic metabolism (CYP2D6); Chlorthalidone: excreted unchanged in urine. |
| Excretion | Renal excretion accounts for approximately 50% of elimination, with 30% as unchanged drug and 20% as metabolites; biliary/fecal elimination accounts for about 10%. |
| Half-life | Terminal elimination half-life is 4-6 hours; may be prolonged in renal impairment, requiring dose adjustment. |
| Protein binding | Approximately 90% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | 0.8-1.0 L/kg, indicating extensive tissue distribution; higher Vd may correlate with prolonged effect. |
| Bioavailability | Oral bioavailability is 60-70% due to first-pass metabolism; intravenous bioavailability is 100%. |
| Onset of Action | Oral: 1-2 hours; Intravenous: 5-10 minutes; onset of antihypertensive effect correlates with peak plasma concentrations. |
| Duration of Action | 8-12 hours; clinical effect may persist up to 24 hours due to active metabolites; duration may exceed half-life due to tissue binding. |
| Molecular Weight | Clonidine: 230.1 Da; Chlorthalidone: 338.8 Da. (CLORPRES is a combination product; MW of components provided separately.) |
One tablet (clonidine 0.1 mg/chlorthalidone 15 mg) orally once or twice daily; maximum 0.6 mg clonidine/90 mg chlorthalidone daily.
| Dosage form | TABLET |
| Renal impairment | Chlorthalidone is ineffective if GFR <30 mL/min; avoid use. Clonidine requires dose reduction when GFR <10 mL/min; start at 0.1 mg once daily. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B: reduce clonidine dose by 25%. Child-Pugh C: avoid or use with extreme caution; clonidine may precipitate encephalopathy. |
| Pediatric use | Not recommended for children; safety and efficacy not established. |
| Geriatric use | Start with clonidine 0.1 mg chlorthalidone 15 mg once daily; monitor for orthostatic hypotension, bradycardia, and electrolyte disturbances. Titrate slowly every 2 weeks. |
| 1st trimester | Avoid in first trimester due to risk of fetal harm; use alternative antihypertensives. Case reports suggest potential teratogenicity (neural tube defects, cardiovascular malformations) with clonidine (component). |
| 2nd trimester | Use only if benefit outweighs risk; may cause fetal bradycardia, decreased placental perfusion. Monitor fetal heart rate and growth. |
| 3rd trimester | Avoid near term due to risk of neonatal hypotension, bradycardia, and withdrawal (irritability, feeding problems). Discontinue 2-3 days before delivery if possible. |
Clinical note
Comprehensive clinical and safety monograph for CLORPRES (CLORPRES).
| Placental transfer | Clonidine crosses the placenta (cord blood/maternal serum ratio ~0.9). Chlorthalidone likely crosses but data limited. Both can affect fetal hemodynamics. |
| Breastfeeding | Clonidine and chlorthalidone are excreted into breast milk. Clonidine levels are low but may cause infant sedation, bradycardia, or hypotension. Chlorthalidone may reduce milk supply. Use with caution; alternatives preferable. |
| Lactation Rating | L3 (Moderately Safe) - consider risk-benefit; monitor infant for side effects. |
| Teratogenic Risk | Pregnancy Category C. First trimester: risk of fetal bradycardia, oligohydramnios, and growth restriction due to reduced placental perfusion. Second/third trimester: potential for neonatal hypotension, respiratory depression, and electrolyte disturbances. Avoid use in pregnancy unless benefit outweighs risk. |
| Fetal Monitoring | Monitor maternal blood pressure, heart rate, and serum electrolytes. Fetal heart rate monitoring for bradycardia. Ultrasound for fetal growth and amniotic fluid index. |
| Fertility Effects | No documented adverse effects on fertility. Limited data; theoretical risk due to hemodynamic changes. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to clonidine, chlorthalidone, or sulfonamide-derived drugs (e.g., thiazides)AnuriaSevere renal impairment (CrCl <30 mL/min)Known hypersensitivity to any component
| Precautions | Rebound hypertension with abrupt clonidine withdrawal, Hypokalemia due to chlorthalidone, Bradycardia and syncope, Renal impairment: monitor electrolytes |
| Food/Dietary | Avoid high-sodium foods as they can counteract the antihypertensive effect. Limit alcohol intake. Chlorthalidone may cause potassium depletion; consider potassium-rich foods (bananas, oranges, spinach) unless contraindicated. Grapefruit juice may increase clonidine levels; avoid excessive intake. |
| Clinical Pearls | Clorpres (clonidine + chlorthalidone) combines central alpha-2 agonist with thiazide diuretic. Monitor for orthostatic hypotension, especially in elderly. Rebound hypertension upon abrupt clonidine discontinuation is dangerous; taper over 2-4 days. Chlorthalidone may cause hypokalemia; check potassium levels regularly. Avoid use in patients with history of depression or severe bradycardia. |
| Patient Advice | Take the medication exactly as prescribed, usually once daily in the morning to prevent nighttime urination. · Do not stop taking this medication suddenly; stopping abruptly can cause a severe rise in blood pressure. · Rise slowly from sitting or lying down to prevent dizziness or fainting. · Avoid alcohol, which can worsen side effects like dizziness and drowsiness. · Report signs of low potassium (muscle cramps, weakness, irregular heartbeat) or dehydration (excessive thirst, dry mouth, dark urine). |
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