Generic Name

Phenoxybenzamine Hydrochloride

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Classification

FDA Approved Indications

• Pheochromocytoma (preoperative management)
• Vasoconstrictive states

Mechanism of Action

Phenoxybenzamine irreversibly binds to alpha-adrenergic receptors, blocking the effects of catecholamines like norepinephrine, leading to vasodilation and decreased blood pressure.

Dosage and Administration

Adult: Initial dose of 10 mg twice daily, titrated based on response. Usual maintenance dose 40-100 mg daily in divided doses.

Pediatric: Not generally used in children due to limited data.

Geriatric: Start at lower doses due to increased sensitivity and risk of hypotension.

Renal Impairment: Use with caution; dose adjustments may be necessary.

Hepatic Impairment: No specific adjustment data available.

Pharmacokinetics

Absorption: Well absorbed orally.

Distribution: Widely distributed with high affinity for alpha-adrenergic receptors.

Metabolism: Metabolized minimally, primarily excreted unchanged.

Excretion: Excreted mainly via urine.

Half Life: Approximately 24 hours.

Contraindications

• Known hypersensitivity to phenoxybenzamine
• Acute myocardial infarction
• Suspected or diagnosed pheochromocytoma with catecholamine surge

Precautions

• Use cautiously in patients with orthostatic hypotension, congestive heart failure, peptic ulcer, or hepatic impairment.

Adverse Reactions - Common

• Postural hypotension (Common)
• Tachycardia (Common)
• Nasal congestion (Common)
• Dizziness (Common)

Adverse Reactions - Serious

• Arrhythmias (Less common)
• Use with caution in patients with arrhythmias or ischemic heart disease (Less common)

Drug-Drug Interactions

• Other antihypertensives (risk of additive hypotension)
• Epinephrine (can cause hypertensive crisis during catecholamine surge)

Drug-Food Interactions

N/A

Drug-Herb Interactions

N/A

Nursing Implications

Patient/Family Teaching

• Rise slowly from sitting or lying positions to reduce orthostatic hypotension.
• Report any dizziness, rapid heartbeat, or swelling.
• Do not abruptly discontinue medication.
• Avoid hot environments and alcohol which can increase risk of hypotension.

Special Considerations

Black Box Warnings:

• Phenoxybenzamine should only be used under medical supervision for approved indications.

Genetic Factors: None specific.

Lab Test Interference: May interfere with some laboratory tests that measure catecholamines.

Overdose Management

Signs/Symptoms: Severe hypotension, tachycardia, dizziness, nausea.

Treatment: Discontinue drug immediately, administer intravenous fluids, and vasopressors if necessary.

Storage and Handling

Storage: Store in a cool, dry place away from light.

Stability: Stable under recommended storage conditions.