HYDRO-SERP "50"
Clinical safety rating
cautionComprehensive clinical and safety monograph for HYDRO-SERP "50" (HYDRO-SERP "50").
Hydrochlorothiazide inhibits the Na+-Cl- symporter in the distal convoluted tubule, increasing excretion of sodium, chloride, and water. Reserpine depletes catecholamines (norepinephrine, dopamine) from peripheral sympathetic nerve endings, reducing vascular tone and heart rate.
| Metabolism | Hydrochlorothiazide is not extensively metabolized. Reserpine is metabolized primarily in the liver by CYP450 enzymes. |
| Excretion | Renal (50-70% as unchanged drug and metabolites), biliary/fecal (20-30%) |
| Half-life | 50-100 hours (prolonged in renal impairment; half-life up to 200 hours in severe renal disease) |
| Protein binding | 90-96% (primarily to albumin and alpha1-acid glycoprotein) |
| Volume of Distribution | 200-400 L/kg (extremely large due to extensive tissue binding, especially in adrenergic nerve terminals) |
| Bioavailability | Oral: 40-50% (extensive first-pass metabolism) |
| Onset of Action | Oral: 3-6 days for full antihypertensive effect (delayed due to gradual depletion of catecholamines); IV: 2-4 hours |
| Duration of Action | Oral: 1-6 weeks (persistent effect after discontinuation due to long half-life and nerve terminal depletion); IV: 6-24 hours |
| Molecular Weight | 297.74 |
Hydrochlorothiazide 50 mg orally once daily.
| Dosage form | TABLET |
| Renal impairment | Contraindicated in anuria. For GFR 30-60 mL/min: reduce dose to 25 mg daily. For GFR <30 mL/min: not recommended. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B/C: use with caution; monitor electrolytes and renal function; reduce dose if needed. |
| Pediatric use | Not typically recommended; safety and efficacy not established. |
| Geriatric use | Initiate at 12.5-25 mg orally once daily; titrate cautiously; monitor electrolytes and renal function. |
| 1st trimester | Hydrochlorothiazide crosses the placenta. Use in first trimester is associated with increased risk of congenital anomalies, particularly neural tube defects and oral clefts. Avoid use if possible. |
| 2nd trimester | May cause fetal or neonatal jaundice, electrolyte imbalances, and thrombocytopenia. Use only if clearly needed and potential benefit outweighs risk. |
| 3rd trimester | Can cause fetal or neonatal thrombocytopenia and electrolyte disturbances. May decrease placental perfusion. Avoid use in pregnancy-induced hypertension as it does not improve outcome and may impair fetal growth. |
Clinical note
Comprehensive clinical and safety monograph for HYDRO-SERP "50" (HYDRO-SERP "50").
| Placental transfer | Hydrochlorothiazide crosses the placenta in small amounts. The fetal/maternal concentration ratio is approximately 0.15. It has been detected in cord blood and amniotic fluid. |
| Breastfeeding | Hydrochlorothiazide is excreted into breast milk in small amounts. In a study, relative infant dose was estimated to be 1.1% of maternal weight-adjusted dose. Effects on the nursing infant are unlikely at typical maternal doses. However, high doses may suppress lactation due to diuretic effect. Monitor infant for jaundice, electrolyte disturbances, and adequate weight gain. |
| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | Hydrochlorothiazide: First trimester: Crosses placenta, risk of fetal or neonatal jaundice, thrombocytopenia, and possibly other adverse effects; limited human data, association with congenital anomalies not established. Second and third trimesters: May cause fetal or neonatal electrolyte disturbances, hypoglycemia, and decreased placental perfusion. Reserpine: First trimester: Animal studies show no teratogenic effects, human data insufficient. Second and third trimesters: May cause neonatal respiratory depression, bradycardia, hypothermia, and nasal congestion due to depletion of catecholamines. |
| Fetal Monitoring | Monitor maternal blood pressure, serum electrolytes (sodium, potassium), renal function, and uric acid. Assess for signs of fetal distress and growth restriction via ultrasound. In neonates, monitor for electrolyte imbalance, hypoglycemia, jaundice, and thrombocytopenia. |
| Fertility Effects | Hydrochlorothiazide: No known direct effect on fertility. Reserpine: May interfere with reproductive function due to central nervous system effects and possible hormonal disturbances; animal studies suggest impaired fertility at high doses. Human data are limited. |
■ FDA Black Box Warning
None
| Serious Effects |
AnuriaSulfonamide allergy (cross-reactivity possible)Severe renal impairment (CrCl <30 mL/min)Hepatic coma or pre-comaHypersensitivity to hydrochlorothiazide or any component
| Precautions | Electrolyte imbalance (especially hypokalemia), Sulfonamide allergy (hydrochlorothiazide), Mental depression (reserpine), Bradycardia and arrhythmias (reserpine) |
| Food/Dietary | Avoid high-sodium foods (e.g., processed meats, canned soups) to prevent fluid retention and counteract antihypertensive effects. Avoid excessive potassium-rich foods (e.g., bananas, oranges, spinach) as thiazides cause potassium loss; however, reserpine may not affect potassium levels. Limit alcohol intake. Take with food or milk to reduce gastrointestinal upset. |
| Clinical Pearls | Hydrochlorothiazide 50 mg plus reserpine 0.125 mg. Monitor serum potassium and magnesium; hypokalemia increases digitalis toxicity risk. Reserpine may cause depression; avoid in patients with history of depression. Onset of antihypertensive effect is 3-6 hours. Use with caution in patients with renal impairment (CrCl <30 mL/min) as thiazides are ineffective. |
| Patient Advice | Take this medication exactly as prescribed, usually once daily in the morning to avoid nighttime urination. · This drug may make you dizzy; avoid driving or operating machinery until you know how it affects you. · Reserpine can cause nasal congestion, drowsiness, or depression; contact your doctor if you experience mood changes. · Avoid alcohol as it may increase dizziness and drowsiness. · Stay hydrated but do not overhydrate; report excessive thirst, dry mouth, or muscle cramps. · Do not stop taking this medication abruptly as it may cause a rapid increase in blood pressure. · If you miss a dose, take it as soon as you remember unless it is almost time for the next dose; do not double the dose. · This medication may increase your sensitivity to sunlight; use sunscreen and protective clothing. |
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