Schedule H

Oral

• Tablets: 0.5 mg, 1 mg, 2 mg, 2.5 mg, 5 mg (immediate-release)

INDICATIONS + DOSING — FOR CLINICIAN USE ONLY

Primary Indications (Approved / Standard in India)

1. Essential Hypertension

Parameter Recommendation

Starting dose: 0.5 mg at bedtime

Titration: Increase by 0.5–1 mg every 5–7 days based on BP response

Usual maintenance dose: 3–15 mg/day in 2–3 divided doses

Maximum dose: 20 mg/day

Clinical notes:

• Initiate at bedtime to minimise first-dose hypotension

• First-dose effect risk highest in volume-depleted or elderly patients

• Not a first-line agent for uncomplicated hypertension in current Indian practice; consider when other classes contraindicated

1. Benign Prostatic Hyperplasia (Symptomatic LUTS)

Parameter Recommendation

Starting dose: 0.5 mg at bedtime

Titration: Increase to 1–2 mg twice daily over 1–2 weeks

Usual maintenance dose: 2–4 mg/day in divided doses

Maximum dose: 10 mg/day for BPH

Clinical notes:

• Provides symptomatic relief of lower urinary tract symptoms only

• Does not reduce prostate size or PSA levels

• Tamsulosin or alfuzosin often preferred due to better uroselective profile

Secondary Indications — Adults (Off-label)

Indication Dose Duration Notes

PTSD-associated nightmares (OFF-LABEL) Starting dose: 1 mg at bedtime; Titration: increase by 1 mg every 3–5 nights; Usual dose: 2–6 mg at bedtime; Maximum: 15 mg/night Continue if therapeutic benefit observed Specialist only. Evidence: Multiple RCTs; supported by Indian psychiatric specialist practice

Raynaud's phenomenon (OFF-LABEL) Starting dose: 0.5 mg twice daily; Titration: increase to 1–2 mg thrice daily; Usual dose: 3–6 mg/day; Maximum: 10 mg/day As long as clinically beneficial Specialist only. Second-line when CCBs ineffective or contraindicated. Evidence: RCTs, specialist practice

Scorpion sting envenomation (adjunct) (OFF-LABEL) 0.25–0.5 mg IV or 0.5 mg oral in adults (single dose, may repeat) Single or short-term use Specialist only. Evidence: Indian toxicology practice, AIIMS protocols for autonomic storm management

PAEDIATRIC DOSING (Specialist Only)

Primary Indications (Approved / Standard in India)

Hypertension in Children

Age/Weight Starting Dose Titration Maintenance Range Maximum

Children ≥6 years 0.05 mg/kg/dose once daily at bedtime Increase every 5–7 days 0.05–0.1 mg/kg/dose given 2–3 times daily 0.4 mg/kg/day or 15 mg/day (whichever is lower)

Safety monitoring:

• Blood pressure (supine and standing) before each dose increase

• Monitor for orthostatic symptoms, dizziness, syncope

• Avoid first-dose effect: counsel caregiver on initial bedtime dosing

Minimum age: Not recommended below 6 years except under paediatric nephrology or cardiology supervision

Secondary Indications — Paediatrics (Off-label)

Indication Dose Notes

Scorpion sting envenomation (adjunct) (OFF-LABEL) 0.01–0.03 mg/kg oral or IV (single dose) Specialist only. Evidence: Indian paediatric toxicology protocols (AIIMS, PGI Chandigarh)

Statement: Not recommended below 6 years for any indication except under specialist supervision in tertiary care settings.

30 No dose adjustment required

15–30 Use lower starting dose (0.5 mg); titrate cautiously

<15 or dialysis Start at lowest dose; closely monitor BP; minimal dialysis clearance — no supplemental dose needed

• Known hypersensitivity to prazosin or other quinazoline derivatives

• Concurrent use with potent PDE-5 inhibitors (sildenafil, tadalafil, vardenafil) at initiation of prazosin therapy

• Severe uncontrolled heart failure with low cardiac output

• Significant aortic or mitral stenosis (haemodynamically significant)

• History of orthostatic hypotension or syncope

• Volume depletion, dehydration, or concurrent diuretic use

• Elderly patients — high risk of falls and postural symptoms

• Patients scheduled for cataract surgery — inform ophthalmologist (risk of intraoperative floppy iris syndrome)

• Recent myocardial infarction — initiate only after haemodynamic stabilisation

• Heart failure — monitor fluid status; may worsen symptoms in preload-dependent states

• Avoid abrupt discontinuation after prolonged use

Parameter Information

Overall safety: Limited human data; animal studies show no clear teratogenicity

Risk category: Not formally classified in India; use only if clearly needed

Preferred alternatives: Labetalol, methyldopa, nifedipine (for gestational hypertension)

When may be used: Only when standard agents contraindicated and benefit outweighs risk; specialist decision only

What to monitor: Maternal BP (particularly postural), fetal growth, uteroplacental perfusion

Parameter Information

Compatible with breastfeeding: Limited data; generally considered acceptable with caution

Drug levels in milk: Low (minimal excretion expected)

Preferred alternatives: Labetalol, nifedipine (better studied in breastfeeding)

What to monitor in infant: Feeding pattern, excessive sedation, weight gain, signs of hypotension

Parameter Recommendation

Starting dose: 0.5 mg at bedtime

Titration: Very slow — increase no more frequently than weekly

Extra risks: Postural hypotension, syncope, falls with fractures, confusion, nocturnal hypotension

Special considerations: Review concurrent medications (diuretics, other antihypertensives); ensure adequate hydration

Interacting Drug Effect Recommendation

PDE-5 inhibitors (sildenafil, tadalafil, vardenafil) Severe additive hypotension Avoid co-initiation; if both required, ensure prazosin dosing is stable, then introduce PDE-5 inhibitor at lowest dose with ≥4-hour gap

Other alpha-blockers (tamsulosin, alfuzosin, doxazosin) Excessive alpha-blockade, profound hypotension Avoid combination

Potent antihypertensives (nitrates, hydralazine) Marked additive BP lowering Avoid concurrent initiation; dose adjustment required

MAO inhibitors Enhanced hypotensive effect Avoid or use with extreme caution

Interacting Drug Effect Recommendation

Beta-blockers Additive hypotension, bradycardia Can be used together; start low, monitor BP

Diuretics Synergistic BP lowering; postural hypotension risk May need to reduce diuretic dose temporarily

NSAIDs May blunt antihypertensive effect Monitor BP; consider dose adjustment

Calcium channel blockers Additive vasodilation Monitor BP closely

Tricyclic antidepressants Additive hypotension Monitor; counsel patient

Alcohol Enhanced first-dose hypotensive effect Counsel to avoid alcohol, especially during initiation

Rifampicin May reduce prazosin levels (CYP induction) Monitor BP; may need higher prazosin dose

• Dizziness (most common)

• Headache

• Drowsiness and fatigue

• Postural hypotension

• Palpitations

• Nausea

• Nasal congestion

• Weakness and lethargy

Adverse Effect Action

First-dose syncope Occurs within 30–90 minutes of initial dose; patient should lie down; ensure volume repletion; restart at lower dose if clinically appropriate

Severe hypotension May require IV fluids; rarely, vasopressors; hospitalise if unresponsive

Intraoperative floppy iris syndrome (IFIS) Irreversible; must inform ophthalmologist before cataract surgery

Priapism Medical emergency; requires urological intervention; discontinue drug immediately

Angioedema (rare) Discontinue immediately; manage airway if needed

Phase Parameters

Baseline Blood pressure (sitting and standing), heart rate, renal function, hepatic function

After initiation/dose change BP and postural symptoms within 2–4 hours of first dose or any dose increase; repeat for first 3–5 days

Long-term BP at each visit, orthostatic tolerance assessment, renal function (if on concurrent diuretics), symptom review for LUTS if used for BPH

• Minipress (Pfizer)

• Prazopress (Sun Pharma)

• Prazocip (Cipla)

• Prazosin (generic — multiple manufacturers)

Note: No significant FDCs relevant to clinical use.

Strength Approximate Price (per 10 tablets)

2.5 mg ₹30–₹60

• NLEM status: Not currently listed under NLEM 2022

• Government supply: Available through Jan Aushadhi at reduced prices

• Private retail: Widely available

1. First-dose precaution: Always initiate prazosin at bedtime with the patient lying down; advise the patient to rise slowly from bed the next morning.

1. PDE-5 inhibitor caution: If a patient on stable prazosin therapy requires a PDE-5 inhibitor, introduce it at the lowest dose and separate dosing by at least 4 hours.

1. Cataract surgery alert: Prazosin (even if discontinued) can cause IFIS — always ask about alpha-blocker history before ophthalmic surgery.

1. BPH preference: For isolated LUTS/BPH, tamsulosin or alfuzosin are often preferred due to better uroselectivity and fewer systemic BP effects.

1. Scorpion sting use: In regions endemic for Mesobuthus tamulus (Indian red scorpion), prazosin is an important adjunct for managing catecholamine storm — know the dose.

1. Not first-line for hypertension: In current Indian practice, CCBs, ARBs, or ACE inhibitors are preferred for uncomplicated hypertension; reserve prazosin for special situations.

prazosin; alpha-blocker; hypertension; BPH; LUTS; PTSD-nightmares; scorpion-sting; Raynaud; elderly-caution; first-dose-syncope; Schedule-H

RxIndia v0.4 — 09 Jan 2025

• CDSCO-approved product inserts

• Indian Pharmacopoeia

• NFI 2021

• API Textbook of Medicine, 12th edition

• AIIMS Hypertension Management Protocol

• AIIMS Toxicology Protocol (scorpion envenomation)

• Goodman & Gilman's The Pharmacological Basis of Therapeutics

• IAP Guidelines (paediatric use — supportive)

• RCTs/meta-analyses (for PTSD off-label use — Raskind et al., multiple trials)