Phentolamine


Generic Medicine Info
Indications and Dosage
Injection
Dermal necrosis associated with norepinephrine IV infusion
Adult: As phentolamine mesilate: Prevention: 10 mg is added to each litre of solution containing norepinephrine. Treatment of extravasation of norepinephrine: 5-10 mg (diluted in 10 mL 0.9% NaCl) is injected via local infiltration into the affected area within 12 hours.

Intramuscular, Intravenous
Diagnosis of phaeochromocytoma
Adult: Reserved for cases in which additional confirmatory test is necessary and after risks associated with use have been considered: As phentolamine mesilate: Recommended dose: 5 mg via rapid IV inj (after pressor response to venipuncture has subsided) or IM inj. Record blood pressure immediately after inj, every 30 seconds for the 1st 3 minutes, then every 1 minute for the next 7 minutes (IV inj); or every 5 minutes for 30-45 minutes (IM inj). Patient must rest in a supine position during the test preferably in a quiet, darkened room. Delay the inj until blood pressure is stabilised by monitoring every 10 minutes for at least 30 minutes. Withhold analgesics, sedatives and all other medications except for essential drugs (e.g. digitalis, insulin) for at least 24 hours and preferably 48-72 hours before the test. Refer to the detailed product or local guideline for interpretation of response.
Child: Reserved for cases in which additional confirmatory test is necessary and after risks associated with use have been considered: As phentolamine mesilate: Recommended dose: 1 mg via rapid IV inj (after pressor response to venipuncture has subsided) or 3 mg via IM inj. Record blood pressure immediately after IV inj, at 30-second intervals for the 1st 3 minutes, then at 60-second intervals for the next 7 minutes; or every 5 minutes for 30-45 minutes after IM inj. Patient must rest in a supine position during the test preferably in a quiet, darkened room. Delay the inj until blood pressure is stabilised by checking every 10 minutes for at least 30 minutes. Withhold analgesics, sedatives and all other medications except for essential drugs (e.g. digitalis, insulin) for at least 24 hours and preferably 48-72 hours before the test. Refer to the detailed product or local guideline for interpretation of response.

Intramuscular, Intravenous
Hypertension in phaeochromocytoma
Adult: As phentolamine mesilate: For prevention or control of cases: Preoperative reduction of elevated blood pressure: 5 mg via IV or IM inj given 1 or 2 hours prior to surgery, may be repeated if necessary. During surgery: 5 mg via IV inj as indicated.
Child: As phentolamine mesilate: For prevention or control of cases: Preoperative reduction of elevated blood pressure: 1 mg via IV or IM inj given 1 or 2 hours prior to surgery, may be repeated if necessary. During surgery: 1 mg via IV inj as indicated.
Reconstitution
Powder for inj: Reconstitute vial labelled as 5 mg with 1 mL sterile water for injection to a concentration of 5 mg/mL solution. For extravasation treatment: Further dilute 5-10 mg in 10 mL 0.9% NaCl.
Contraindications
Existing or history of MI, coronary insufficiency, angina, other evidence suggestive of coronary artery disease.
Special Precautions
Patient with history of CV disease; gastritis or peptic ulcer. Pregnancy and lactation.
Adverse Reactions
Significant: Tachycardia, cardiac arrhythmias.
Gastrointestinal disorders: Nausea, vomiting, diarrhoea.
General disorders and administration site conditions: Weakness.
Nervous system disorders: Dizziness.
Respiratory, thoracic and mediastinal disorders: Nasal stuffiness.
Vascular disorders: Acute and prolonged hypotensive episodes, orthostatic hypotension, flushing.
Potentially Fatal: MI, cerebrovascular spasm or occlusion.
IM/IV/Parenteral: C
Monitoring Parameters
Monitor blood pressure, heart rate, extravasation site; signs and symptoms of orthostasis. Evaluate cardiac status.
Overdosage
Symptoms: CV disturbances (e.g. arrhythmias, hypotension, tachycardia, shock), excitation, headache, visual disturbances, sweating, pupillary contraction, nausea, vomiting, diarrhoea, and hypoglycaemia. Management: Supportive treatment. Raise the patient's leg and administer plasma expander. May give IV infusion of norepinephrine, if necessary, then titrate to maintain blood pressure at normotensive level; do not use epinephrine.
Action
Description: Phentolamine is a competitive and non-selective α-adrenergic blocker that briefly antagonises the circulating norepinephrine and epinephrine, thus reducing hypertension caused by α effects of these catecholamines and decreasing tissue injury due to extravasation of these along with other sympathomimetic vasoconstrictors. It also has positive inotropic and chronotropic effects on the cardiac muscle.
Onset: 1-2 minutes (IV); 15-20 minutes (IM).
Duration: 10-30 minutes (IV); 30-45 minutes (IM).
Pharmacokinetics:
Metabolism: Extensively metabolised in the liver.
Excretion: Via urine (approx 13% as unchanged drug). Elimination half-life: 19 minutes (IV).
Chemical Structure

Chemical Structure Image
Phentolamine

Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 5775, Phentolamine. https://pubchem.ncbi.nlm.nih.gov/compound/Phentolamine. Accessed Sept. 24, 2021.

Storage
Powder for inj: Intact vial: Store between 20-25°C. Use the reconstituted solution upon preparation; do not store the solution.
MIMS Class
Other Antihypertensives
ATC Classification
C04AB01 - phentolamine ; Belongs to the class of imidazoline derivative agents. Used as peripheral vasodilators.
References
Anon. Phentolamine Mesylate. AHFS Clinical Drug Information [online]. Bethesda, MD. American Society of Health-System Pharmacists, Inc. https://www.ahfscdi.com. Accessed 10/09/2021.

Anon. Phentolamine. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 04/08/2021.

Buckingham R (ed). Phentolamine Mesilate. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 04/08/2021.

Phentolamine Mesylate Injection (Precision Dose Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 04/08/2021.

Phentolamine Mesylate Injection (Tagi Pharma, Inc.). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 10/09/2021.

Disclaimer: This information is independently developed by MIMS based on Phentolamine 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 © 2022 MIMS. All rights reserved. Powered by MIMS.com
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