HYDRO-RESERP

Clinical safety rating: caution

Comprehensive clinical and safety monograph for HYDRO-RESERP (HYDRO-RESERP).

How it works

Hydrochlorothiazide is a thiazide diuretic that inhibits the sodium-chloride symporter in the distal convoluted tubule, reducing reabsorption of sodium and chloride and promoting diuresis. Reserpine is a Rauwolfia alkaloid that depletes catecholamines (norepinephrine, dopamine, serotonin) from adrenergic nerve endings and brain, leading to reduced sympathetic outflow and vasodilation.

What the body does with it

Metabolism	Hydrochlorothiazide is not extensively metabolized; it is excreted unchanged in urine. Reserpine is extensively metabolized in the liver by hydrolysis and conjugation.
Excretion	Renal: 30-40% as unchanged reserpine; biliary/fecal: 60-70% as metabolites.
Half-life	50-100 hours (terminal); prolonged in renal impairment, leading to accumulation on repeated dosing.
Protein binding	96% bound to albumin and alpha1-acid glycoprotein.
Volume of Distribution	1.5-2.5 L/kg; extensive tissue distribution with high affinity for adrenergic neurons.
Bioavailability	Oral: 50-60% (first-pass metabolism); IM: ~100%.
Onset of Action	Oral: 3-6 days; IM: 2-4 hours; IV: 30-60 minutes.
Duration of Action	Oral: 1-6 weeks after discontinuation due to irreversible binding to adrenergic vesicles; IM/IV: 4-12 hours.

Classification & Brands

Dosing & administration

HYDRO-RESERP contains hydrochlorothiazide (HCTZ) and reserpine. HCTZ: 25-100 mg daily orally; reserpine: 0.125-0.25 mg daily orally. Administer once daily unless intolerable hypotension; then split doses. Avoid doses exceeding HCTZ 100 mg/day and reserpine 0.25 mg/day.

Dosage form	TABLET
Renal impairment	Contraindicated if eGFR <30 mL/min/1.73m² due to HCTZ ineffectiveness. For GFR 30-50 mL/min: reduce HCTZ to 12.5-25 mg daily; reserpine unchanged. Monitor serum creatinine and electrolytes. Not recommended for anuric patients.
Liver impairment	Child-Pugh A: no adjustment. Child-Pugh B: reduce HCTZ by 25-50% (start at 12.5 mg) due to risk of electrolyte imbalance; reserpine: use lowest effective dose (0.125 mg) and monitor for encephalopathy. Child-Pugh C: avoid HCTZ; reserpine contraindicated due to risk of hepatic coma.
Pediatric use	Not approved for pediatric use. Limited data: HCTZ 1-2 mg/kg/day orally once or divided; max 50 mg/day. Reserpine 0.01-0.02 mg/kg/day in 1-2 doses; max 0.25 mg/day. Monitor growth, electrolytes, and blood pressure closely in children.
Geriatric use	Start at half the adult dose: HCTZ 12.5 mg orally daily; reserpine 0.05-0.1 mg daily. Titrate slowly (every 2-4 weeks). Monitor for orthostatic hypotension, electrolyte disturbances, depression (reserpine), and dehydration. Avoid in frail elderly due to increased fall risk.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for HYDRO-RESERP (HYDRO-RESERP).

Breastfeeding	Reserpine is excreted into breast milk. M/P ratio approximately 1.6. Potential for infant bradycardia, nasal congestion, and lethargy. Contraindicated in nursing mothers due to risks.
Teratogenic Risk	Reserpine crosses the placenta. First trimester: limited human data but animal studies suggest risk; consider alternative if possible. Second/third trimester: may cause neonatal respiratory depression, bradycardia, hypothermia, and nasal congestion. Avoid in preeclampsia due to risk of placental hypoperfusion. Risk category C.

Warnings & precautions

■ FDA Black Box Warning

Reserpine may cause mental depression, especially in patients with a history of depression. Risks are dose-related and may persist after discontinuation. Use with caution or avoid in patients with a history of depression.

Side Effect Profile

Serious Effects

Absolute Contraindications

["Hypersensitivity to hydrochlorothiazide, reserpine, or sulfonamide derivatives.","History of depression (especially with reserpine).","Active peptic ulcer or ulcerative colitis (reserpine).","Electroconvulsive therapy (within 1 week).","Severe renal impairment (anuria) or severe hepatic disease.","Pregnancy (especially in second and third trimesters; avoid use)."]

Clinical Precautions

Precautions

["May cause depression with suicidal risk (reserpine).","May cause electrolyte imbalances (hypokalemia, hyponatremia) due to hydrochlorothiazide.","May increase serum uric acid and precipitate gout.","May cause orthostatic hypotension and bradycardia.","Use cautiously in patients with renal impairment or hepatic disease."]

Clinical Tips & Counseling

Drug interactions

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HYDRO-RESERP

Clinical safety rating: caution

Comprehensive clinical and safety monograph for HYDRO-RESERP (HYDRO-RESERP).

How it works

What the body does with it

Metabolism	Hydrochlorothiazide is not extensively metabolized; it is excreted unchanged in urine. Reserpine is extensively metabolized in the liver by hydrolysis and conjugation.
Excretion	Renal: 30-40% as unchanged reserpine; biliary/fecal: 60-70% as metabolites.
Half-life	50-100 hours (terminal); prolonged in renal impairment, leading to accumulation on repeated dosing.
Protein binding	96% bound to albumin and alpha1-acid glycoprotein.
Volume of Distribution	1.5-2.5 L/kg; extensive tissue distribution with high affinity for adrenergic neurons.
Bioavailability	Oral: 50-60% (first-pass metabolism); IM: ~100%.
Onset of Action	Oral: 3-6 days; IM: 2-4 hours; IV: 30-60 minutes.
Duration of Action	Oral: 1-6 weeks after discontinuation due to irreversible binding to adrenergic vesicles; IM/IV: 4-12 hours.

Classification & Brands

Dosing & administration

Dosage form	TABLET
Renal impairment	Contraindicated if eGFR <30 mL/min/1.73m² due to HCTZ ineffectiveness. For GFR 30-50 mL/min: reduce HCTZ to 12.5-25 mg daily; reserpine unchanged. Monitor serum creatinine and electrolytes. Not recommended for anuric patients.
Liver impairment	Child-Pugh A: no adjustment. Child-Pugh B: reduce HCTZ by 25-50% (start at 12.5 mg) due to risk of electrolyte imbalance; reserpine: use lowest effective dose (0.125 mg) and monitor for encephalopathy. Child-Pugh C: avoid HCTZ; reserpine contraindicated due to risk of hepatic coma.
Pediatric use	Not approved for pediatric use. Limited data: HCTZ 1-2 mg/kg/day orally once or divided; max 50 mg/day. Reserpine 0.01-0.02 mg/kg/day in 1-2 doses; max 0.25 mg/day. Monitor growth, electrolytes, and blood pressure closely in children.
Geriatric use	Start at half the adult dose: HCTZ 12.5 mg orally daily; reserpine 0.05-0.1 mg daily. Titrate slowly (every 2-4 weeks). Monitor for orthostatic hypotension, electrolyte disturbances, depression (reserpine), and dehydration. Avoid in frail elderly due to increased fall risk.

Use during pregnancy

1st trimester	Consult provider
2nd trimester	Consult provider
3rd trimester	Consult provider

Clinical note

Comprehensive clinical and safety monograph for HYDRO-RESERP (HYDRO-RESERP).

Breastfeeding	Reserpine is excreted into breast milk. M/P ratio approximately 1.6. Potential for infant bradycardia, nasal congestion, and lethargy. Contraindicated in nursing mothers due to risks.
Teratogenic Risk	Reserpine crosses the placenta. First trimester: limited human data but animal studies suggest risk; consider alternative if possible. Second/third trimester: may cause neonatal respiratory depression, bradycardia, hypothermia, and nasal congestion. Avoid in preeclampsia due to risk of placental hypoperfusion. Risk category C.