Phenoxybenzamine


Concise Prescribing Info
Indications/Uses
Hypertension in phaeochromocytoma.
Dosage/Direction for Use
Adult : PO Initial: 10 mg once daily or bid, gradually increased daily by 10 mg increments, according to patient’s response. Maintenance: 1-2 mg/kg/day in 2 divided doses.
Dosage Details
Oral
Hypertension in phaeochromocytoma
Adult: Initially, 10 mg once daily or bid, gradually increased daily by 10 mg increments, according to patient’s response. Maintenance: 1-2 mg/kg daily in 2 divided doses.
Child: 1-2 mg/kg daily.
Elderly: 10 mg daily.
Contraindications
CVA, recovery period (usually 3-4 weeks) after acute MI, conditions where a decrease in blood pressure may be undesirable (e.g. coronary artery disease, stroke).
Special Precautions
Patient with heart failure, CHF, cerebrovascular diseases, cerebral or coronary atherosclerosis, respiratory infections. Renal impairment. Elderly. Children. Pregnancy and lactation.
Adverse Reactions
Significant: Postural hypotension with dizziness, compensatory tachycardia.
Eye disorders: Miosis.
Gastrointestinal disorders: Gastrointestinal upset.
General disorders and admininistration site conditions: Fatigue.
Psychiatric disorders: Drowsiness.
Reproductive system and breast disorders: Inhibition of ejaculation.
Respiratory, thoracic and mediastinal disorders: Nasal congestion.
Patient Counseling Information
This drug may cause dizziness and drowsiness, if affected, do not drive or operate machinery.
MonitoringParameters
Regularly monitor blood pressure especially after each dose adjustment; pulse, orthostatics.
Overdosage
Symptoms: Profound hypotension leading to dizziness or fainting, tachycardia, collapse, vomiting, lethargy, shock. Management: Symptomatic and supportive treatment. Induce vomiting and/or gastric lavage. Treat hypotension with plasma expanders and by postural measures.
Drug Interactions
Increased hypotensive effect and tachycardia with stimulators of both α- and β-receptors (e.g. epinephrine).
Action
Description: Phenoxybenzamine covalently binds to α-receptors causing long lasting non-competitive inhibition of postganglionic synapses thus blocking the effects of epinephrine and norepinephrine at α1 and α2 receptors causing arterial and venous vasodilation and reflex tachycardia.
Onset: Within 2 hr.
Duration: ≥3-4 days.
Pharmacokinetics:
Absorption: Incompletely and variably absorbed from the gastrointestinal tract. Bioavailability: 20-30%.
Distribution: Distributed and accumulates in the adipose tissues.
Metabolism: Metabolised in the liver via dealkylation into N-phenoxyisopropyl-benzylamine.
Excretion: Mainly via urine and bile. Elimination half-life: Approx 24 hour.
Chemical Structure

Chemical Structure Image
Phenoxybenzamine

Source: National Center for Biotechnology Information. PubChem Database. Phenoxybenzamine, CID=4768, https://pubchem.ncbi.nlm.nih.gov/compound/Phenoxybenzamine (accessed on Jan. 22, 2020)

Storage
Store between 20-25°C.
Avoid contact with skin or mucous membranes by wearing gloves and protective equipment. Wash hands before and after handling.
ATC Classification
C04AX02 - phenoxybenzamine ; Belongs to the class of other peripheral vasodilators.
References
Anon. Phenoxybenzamine. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 31/10/2017.

Buckingham R (ed). Phenoxybenzamine Hydrochloride. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 18/10/2017.

Joint Formulary Committee. Phenoxybenzamine Hydrochloride. British National Formulary [online]. London. BMJ Group and Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 18/10/2017.

McEvoy GK, Snow EK, Miller J et al (eds). Phenoxybenzamine Hydrochloride. AHFS Drug Information (AHFS DI) [online]. American Society of Health-System Pharmacists (ASHP). https://www.medicinescomplete.com. Accessed 18/10/2017.

Phenoxybenzamine Hydrochloride Capsule (West-Ward Pharmaceuticals Corp.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed/. Accessed 31/10/2017.

Disclaimer: This information is independently developed by MIMS based on Phenoxybenzamine 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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