Phentolamine
Mechanism :
A drug that Blocks alpha-adrenergic receptors to temporarily antagonise circulating epinephrine and norepinephrine, reducing hypertension caused by endogenous catecholamine alpha effects.
Indication :
- Used in pheochromocytoma diagnosis , pheochromocytoma surgery and reversal of dental anaesthesia.
Contraindications :
CAUTIONS- The first dose effect can occur, resulting in a sudden and drastic drop in blood pressure following administration of the first dose.
Syncope /Hypotension may occur during the first few doses or as the dose is increased; minimise by taking a small first dose at bedtime. Gradually increase the dose.
Following parenteral administration of phentolamine, there have been reports of myocardial infarction, cerebrovascular spasm, and cerebrovascular occlusion; these events were usually associated with marked hypotensive episodes producing shock-like states.
Despite the rarity of tachycardia and cardiac arrhythmias following the administration of phentolamine or other alpha-adrenergic blocking medications, doctors should be alert for the warning signs and symptoms of these conditions, especially in patients with a history of cardiovascular illness. Stop using if angina starts to develop or gets worse.
Dosing :
Injection powder: 5 mg
Injectable solution: 0.4 mg/1.7 mL.
Weight based regimen for pheochromocytoma diagnosis - 0.1-0.2 mg/kg IV/IM, OR 1 mg IV OR 3 mg IM.
Weight based regimen for pheochromocytoma surgery - 1 mg IV/IM OR 0.05-0.1 mg/kg/dose 1-2 hours before surgery, repeat every 2-4 hours until hypertension is controlled; maximum dose is 5 mg.
For reversal of dental anesthesia – Indicated for the reversal of soft-tissue anaesthesia caused by vasoconstrictor-containing intraoral local anaesthesia.Less than 6 years or less than 15 kg. Safety and efficacy have not been established. Dose is determined by the amount of local anaesthetic used. Use the same administration sites and techniques (infiltration or block injection) as for local anaesthetic.
6-12 years (15-30 kg):
Use OraVerse for 1/2 cartridge local anaesthetic. a half cartridge (0.2 mg).
6-12 years (over 30 kg):
1/2 local anaesthetic cartridge: OraVerse a half cartridge (0.2 mg), 1 local anaesthetic cartridge: Cartridge for OraVerse 1 (0.4 mg).
IV Compatibilities:
Preparation For IV:
1 mL SWI (5 mg/mL solution) reconstituted.
Administration of IV/IM:
Inject intravenously or intramuscularly; Rapid IV therapy.
Adverse Effect :
common side effects are nasal congestion, injection site pain , post treatment pain, diarrhoea
Possible side effects can also be cardiac arrest, chest pain, hypotension, myocardial infarction
Interaction :
there’s a documented serious contraindication when phentolamine is used with the following drugs – lofexidine, sildenafil, tamsulosin, vardenafil, yohimbe
Lactation :
It is not advised because it is unclear whether this drug is excreted in breast milk.
Pregnanacy :
Category C - If the benefits outweigh the risks, use with caution. Animal studies indicate a risk, but human studies are either unavailable or have not been conducted.