Phentolamine Mesylate
Mechanism :
It is a drug used in the prevention and treatment of vasoconstrictor extravasation and also in the diagnosis of pheochromocytoma.
Indication :
- Prevention or control of hypertensive episodes that may occur in a patient with pheochromocytoma as a result of stress or manipulation during preoperative preparation and surgical excision.
- Prevention or treatment of dermal necrosis and sloughing following intravenous administration or extravasation of norepinephrine.
- Diagnosis of pheochromocytoma by the phentolamine blocking test.
Contraindications :
Myocardial infarction, history of myocardial infarction, coronary insufficiency, angina, or other evidence suggestive of coronary artery disease; hypersensitivity to phentolamine or related compounds.
Dosing :
For prevention of vasoconstrictor extravasation:
10 mg
phentolamine is added to one litre of vasoconstrictor solution.
For treatment of vasoconstrictor extravasation:
5 mg
phentolamine is diluted in 4 ml normal saline. With 25 no. or 26 no. needle, 0.2 ml is injected at 5 sites around the infiltration.
For diagnosis of pheochromocytoma:
0.1-0.2 mg/kg/dose IV/IM or 1 mg IV or 3 mg IM.
For treatment of hypertension during surgery:
0.05-0.1 mg/kg/dose or 1-2 mg IV/IM 1-2 hours before operation; repeat every 2-4 hours until hypertension has been controlled; Maximum dose: 5 mg/dose.
Adverse Effect :
Post-treatment and injection site pain, hypotension, tachycardia, arrhythmias, nasal congestion, vomiting, diarrhoea and exacerbation of peptic ulcer.
Interaction :
Tadalafil: Consumer information for this minor interaction is not currently available. Some minor drug interactions may not be clinically relevant in all patients. Minor drug interactions do not usually cause harm or require a change in therapy. However, the healthcare provider can determine if adjustments to medications are needed.
Sildenafil: Sildenafil can add to the blood pressure-lowering effect of phentolamine. May experience signs and symptoms of low blood pressure such as dizziness, light-headedness, fainting, flushing, headache, or a rapid pulse or heart rate. More likely to experience these problems at the beginning of treatment, following a dose increase, or when treatment is restarted after an interruption.
Renal Dose :
Dose in Renal Impairment GFR (mL/min)
| 20-50 | Dose as in normal renal function |
| 10-20 | Dose as in normal renal function |
| <10 | Dose as in normal renal function Titrate dose to end point, i.e. lower BP |
Dose in Patients undergoing Renal Replacement Therapies
| CAPD | Unknown dialysability. Dose as in normal renal function |
| HD | Unknown dialysability. Dose as in normal renal function |
| HDF/High flux | Unknown dialysability. Dose as in normal renal function |
| CAV/VVHD | Unknown dialysability. Dose as in normal renal function |
Hepatic Dose :
No dosage adjustments are recommended.