HYDRALAZINE HYDROCHLORIDE, HYDROCHLOROTHIAZIDE AND RESERPINE
Clinical safety rating: safe
MAOIs can cause excitability and hypertension Can cause depression and suicidal ideation.
Hydralazine is a direct-acting vasodilator that relaxes arterial smooth muscle, reducing peripheral vascular resistance. Hydrochlorothiazide is a thiazide diuretic that inhibits sodium and chloride reabsorption in the distal convoluted tubule, decreasing plasma volume and cardiac output. Reserpine depletes catecholamines from adrenergic nerve endings, reducing sympathetic tone and lowering blood pressure.
| Metabolism | Hydralazine: N-acetylation (hepatic, NAT2); Hydrochlorothiazide: minimal hepatic metabolism, mostly excreted unchanged; Reserpine: extensive hepatic metabolism (CYP3A4, CYP2D6). |
| Excretion | Hydralazine: 90% renal (as metabolites, 5-10% unchanged), 10% fecal. Hydrochlorothiazide: >95% renal (unchanged). Reserpine: 30-50% renal (as metabolites), 40-60% fecal (unchanged and metabolites). |
| Half-life | Hydralazine: 3-7 hours (terminal; prolonged in renal impairment; acetylator phenotype affects clearance; slow acetylators have higher AUC). Hydrochlorothiazide: 6-15 hours (terminal; prolonged in renal impairment, up to 24 h in severe dysfunction). Reserpine: 50-100 hours (terminal; biphasic with α-phase 4.5 h; prolonged in liver disease). |
| Protein binding | Hydralazine: 85-90% (albumin; binding reduced in uremia). Hydrochlorothiazide: 65-70% (albumin). Reserpine: 96% (albumin and lipoproteins). |
| Volume of Distribution | Hydralazine: 1.6 L/kg (large due to tissue binding; penetrates vascular smooth muscle). Hydrochlorothiazide: 0.8 L/kg (restricted to extracellular fluid). Reserpine: 10-15 L/kg (extensive tissue distribution; accumulates in adipose and brain). |
| Bioavailability | Hydralazine: Oral 40-60% (first-pass metabolism; slow acetylators have higher bioavailability). Hydrochlorothiazide: Oral 65-75% (food may increase). Reserpine: Oral 30-50% (extensive gut and liver metabolism). |
| Onset of Action | Hydralazine: Oral 20-30 min (peak effect 1-2 h). Hydrochlorothiazide: Oral 2 h (peak diuresis 4-6 h). Reserpine: Oral 3-6 days (cumulative effect; full antihypertensive effect weeks). |
| Duration of Action | Hydralazine: 6-8 h (immediate-release; extended-release up to 12 h). Hydrochlorothiazide: 6-12 h (diuretic); antihypertensive effect lasts 24 h. Reserpine: 1-6 weeks (prolonged due to irreversible neuronal uptake inhibition; effects persist after discontinuation). |
| Molecular Weight | Hydralazine HCl: 196.64 Da; Hydrochlorothiazide: 297.74 Da; Reserpine: 608.68 Da; Combination product no single MW. |
Oral: 1 tablet (containing 25 mg hydralazine hydrochloride, 25 mg hydrochlorothiazide, and 0.1 mg reserpine) twice daily. Maximum dose: 2 tablets twice daily.
| Dosage form | TABLET |
| Renal impairment | GFR 30-59 mL/min: Reduce dose by 50% or extend interval to every 12-24 hours. GFR 15-29 mL/min: Use with caution, reduce dose by 75% or extend interval to every 24-48 hours. GFR <15 mL/min: Avoid use due to accumulation of active metabolites. |
| Liver impairment | Child-Pugh Class A: No adjustment necessary. Child-Pugh Class B: Reduce dose by 50%. Child-Pugh Class C: Avoid use. |
| Pediatric use | Not recommended for use in pediatric patients due to lack of safety and efficacy data. |
| Geriatric use | Initiate at the lowest available dose (e.g., 1 tablet once daily) and titrate slowly due to increased risk of hypotension, electrolyte disturbances, and central nervous system effects. Monitor renal function and electrolytes closely. |
| 1st trimester | Avoid. Risk of fetal malformations (first trimester exposure associated with cardiovascular and CNS defects). |
| 2nd trimester | Use only if clearly needed. May cause decreased placental perfusion and fetal growth restriction. |
| 3rd trimester | Avoid near term. Reserpine may cause neonatal respiratory depression, bradycardia, and nasal congestion. |
Clinical note
MAOIs can cause excitability and hypertension Can cause depression and suicidal ideation.
| FDA category | Animal |
| Placental transfer | All three components cross the placenta: hydralazine (extensive), hydrochlorothiazide (moderate), reserpine (significant). |
| Breastfeeding |
■ FDA Black Box Warning
None explicitly listed for this combination; however, reserpine carries a warning about increased risk of depression and suicide.
| Common Effects | Depression |
| Serious Effects |
Hypersensitivity to any componentActive peptic ulcer disease (reserpine)Ulcerative colitis (reserpine)Depression (reserpine)Electroshock therapy (reserpine)Anuria (hydrochlorothiazide)Systemic lupus erythematosus (hydralazine)Severe hypersensitivity to sulfonamides (hydrochlorothiazide)
| Precautions | Hydralazine: May induce a lupus-like syndrome, especially in slow acetylators; monitor for fever, arthralgia, rash., Hydrochlorothiazide: May cause hypokalemia, hyponatremia, dehydration; monitor electrolytes; can exacerbate renal impairment., Reserpine: May cause depression, suicidal ideation; avoid in patients with history of depression; may cause bradycardia, nasal congestion. |
| Food/Dietary |
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| Hydralazine and hydrochlorothiazide are excreted into breast milk in low amounts; reserpine is excreted in higher concentrations and may cause adverse effects in nursing infants (diarrhea, lethargy). Avoid breastfeeding due to potential reserpine accumulation. |
| Lactation Rating | L4 - Possibly Hazardous |
| Teratogenic Risk | First trimester: Inadequate human data; animal studies not available. Second and third trimesters: Hydralazine and hydrochlorothiazide are associated with decreased placental perfusion; reserpine has been associated with neonatal respiratory depression, bradycardia, and hypothermia. Hydrochlorothiazide may cause neonatal jaundice, thrombocytopenia, and electrolyte disturbances. |
| Fetal Monitoring | Monitor maternal blood pressure, heart rate, and electrolyte levels (especially potassium, sodium, chloride). Assess fetal growth and amniotic fluid volume via ultrasound. Monitor for signs of neonatal depression (e.g., respiratory rate, heart rate) at birth. |
| Fertility Effects | No well-controlled studies on fertility. Hydralazine and hydrochlorothiazide have no known direct effects on fertility. Reserpine may cause gynecomastia or menstrual irregularities in females and decreased libido in males, potentially affecting fertility. |
| Avoid excessive intake of tyramine-rich foods (aged cheeses, cured meats, fermented foods) due to reserpine component which can potentiate hypertensive crisis. High-sodium foods may counteract antihypertensive effect. Foods high in potassium (bananas, oranges, potatoes, spinach) may be needed to offset potassium loss from hydrochlorothiazide; monitor potassium levels. Grapefruit juice may increase hydralazine absorption; avoid large amounts. |
| Clinical Pearls | Monitor blood pressure closely as first dose may cause exaggerated orthostatic hypotension. Avoid in patients with history of drug-induced lupus; hydralazine may cause lupus-like syndrome. Reserpine depletes catecholamines, leading to nasal congestion, sedation, and increased gastric acid secretion. Hydrochlorothiazide may cause hypokalemia, hyperuricemia, and hyperglycemia. Combine with potassium-sparing diuretic or potassium supplement if needed. Use with caution in renal impairment (hydralazine accumulates). Discontinue reserpine 2 weeks before electroconvulsive therapy due to risk of severe hypotension. |
| Patient Advice | Take this medication exactly as prescribed. Do not stop suddenly as it may cause rapid rise in blood pressure. · This drug may cause dizziness or fainting when standing up quickly. Get up slowly from sitting or lying position. · Avoid alcohol as it can worsen dizziness and lower blood pressure further. · Report any unexplained fever, joint pain, rash, or swelling to your doctor immediately as these could be signs of a lupus-like reaction. · You may experience nasal congestion, drowsiness, or depression. Contact your doctor if these become bothersome. · This combination includes a diuretic (water pill) that increases urination. Take it early in the day to avoid frequent nighttime urination. · Limit foods high in potassium (bananas, oranges, spinach) unless directed; this drug may cause potassium loss. · Use sunscreen and protective clothing as hydrochlorothiazide increases sensitivity to sunlight. · Do not take over-the-counter cold or allergy products containing decongestants without consulting your doctor. |