Prazosin


Concise Prescribing Info
Indications/Uses
Listed in Dosage.
Dosage/Direction for Use
Adult : PO Hypertension Initial: 500 mcg bid or tid for 3-7 days, then increased to 1 mg bid or tid for the next 3-7 days if tolerated, then gradually increase thereafter according to patient's response. Max: 20 mg/day in divided doses. Heart failure Initial: 500 mcg 2-4 times daily, gradually increase according to response. Maintenance: 4-20 mg daily in divided doses. Benign prostatic hyperplasia; Raynaud’s syndrome 500 mcg bid for 3-7 days, adjust dose according to response. Max maintenance dose: 2 mg bid.
Dosage Details
Oral
Benign prostatic hyperplasia, Raynaud's syndrome
Adult: 500 mcg bid for 3-7 days, adjust dose according to response. Max maintenance dose: 2 mg bid.

Oral
Heart failure
Adult: Initially, 500 mcg 2-4 times daily, gradually increase according to response. Maintenance: 4-20 mg daily in divided doses.

Oral
Hypertension
Adult: Initially, 500 mcg bid or tid for 3-7 days, then increased to 1 mg bid or tid for the next 3-7 days if tolerated, then gradually increase thereafter according to patient's response. Max: 20 mg daily in divided doses.
Renal Impairment
Initially, 500 mcg daily, titrate cautiously.
Hepatic Impairment
Initially, 500 mcg daily, titrate cautiously.
Administration
May be taken with or without food. Starting dose is best taken w/ dinner, at least 2-3 hr before retiring. Maintenance doses may be taken w/ or w/o meals.
Special Precautions
Patient with history of micturition in the treatment of benign prostatic hyperplasia (BPH); CHF due to mechanical obstruction (e.g. aortic valve stenosis, mitral valve stenosis, pulmonary embolism, restrictive pericardial disease). Renal and hepatic impairment. Elderly. Pregnancy and lactation.
Adverse Reactions
Significant: Angina, CNS depression, floppy iris syndrome, orthostatic hypotension, syncope, loss of consciousness, priapism.
Cardiac disorders: Dyspnoea, palpitations, tachycardia.
Ear and labyrinth disorders: Tinnitus.
Eye disorders: Reddened sclera, blurred vision, eye pain.
Gastrointestinal disorders: Vomiting, diarrhoea, constipation, dry mouth, abdominal pain.
General disorders and administration site conditions: Asthenia.
Metabolism and nutrition disorders: Oedema.
Nervous system disorders: Paraesthesia, vertigo.
Psychiatric disorders: Insomnia, depression, nervousness.
Respiratory, thoracic and mediastinal disorders: Nasal congestion.
Skin and subcutaneous tissue disorders: Rash.
Vascular disorders: Epistaxis, flushing, vasculitis.
Patient Counseling Information
This drug may cause dizziness and drowsiness, if affected, do not drive or operate machinery.
MonitoringParameters
Monitor blood pressure.
Overdosage
Symptoms: Hypotension, profound drowsiness, depressed reflexes. Management: Symptomatic and supportive treatment. Keep patient in supine position to restore blood pressure and normalise heart rate. If inadequate, administer volume expanders in case of shock. Then, administer vasopressors and angiotensin if necessary. Monitor and support renal function as needed.
Drug Interactions
Additive hypotensive effect with diuretic or other antihypertensive agent (e.g. β-adrenergic blockers). May cause symptomatic hypotension with phosphodiesterase type 5 (PDE5) inhibitors (e.g. sildenafil).
Lab Interference
May give false positive results in screening tests for phaeochromocytoma urinary vanillylmandelic acid (VMA) and methoxyhydroxyphenyl glycol (MHPG) metabolites for norepinephrine.
Action
Description: Prazosin is an alpha blocker that competitively inhibits postsynaptic alpha1-adrenoreceptors in vascular smooth muscles, resulting to vasodilation, and decrease in total peripheral resistance and blood pressure.
Onset: Within 2 hours.
Duration: 10-24 hours.
Pharmacokinetics:
Absorption: Readily absorbed from gastrointestinal tract. Bioavailability: 43-82%. Time to peak plasma concentration: 1-3 hours.
Distribution: Enters breast milk (small amounts). Volume of distribution: 0.5 L/kg. Plasma protein binding: 97%.
Metabolism: Extensively metabolised in the liver via demethylation and conjugation.
Excretion: Mainly via faeces (5-11% as unchanged drug); urine (<10%). Half-life: Approx 2-3 hours; 7 hours (patients with CHF).
Chemical Structure

Click on icon to see table/diagram/image
Storage
Store below 30°C.
ATC Classification
C02CA01 - prazosin ; Belongs to the class of alpha-adrenoreceptor antagonists, peripherally-acting antiadrenergic agents. Used in the treatment of hypertension.
Disclaimer: This information is independently developed by MIMS based on Prazosin from various references and is provided for your reference only. Therapeutic uses, prescribing information and product availability may vary between countries. Please refer to MIMS Product Monographs for specific and locally approved prescribing information. Although great effort has been made to ensure content accuracy, MIMS shall not be held responsible or liable for any claims or damages arising from the use or misuse of the information contained herein, its contents or omissions, or otherwise. Copyright © 2020 MIMS. All rights reserved. Powered by MIMS.com
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