Phenoxybenzamine is a non-selective alpha-adrenergic receptor blocker that acts on the post-ganglionic smooth muscles present in the blood vessels and urinary bladder. It is thus used to treat hypertension associated with pheochromocytoma and urination problems.

Phenoxybenzamine Uses:

• Pheochromocytoma:

  • It is indicated for the treatment of sweating and hypertension associated with pheochromocytoma.

• Off Label Use of Phenoxybenzamine in Adults:

  • It is used in the treatment of hypertensive crisis caused by sympathomimetic amines;
  • It is used for problems of micturition associated with neurogenic bladder, functional outlet obstruction, and partial prostate obstruction.

Other alpha-adrenergic receptor blockers include:

• Tamsulosin (Flomax)
• Alfuzosin (Uroxatral)
• Doxazosin (cardura)

Phenoxybenzamine Dose in Adults

phenoxybenzamine Dose in the treatment of Pheochromocytoma:

• Initial: 10 mg orally two times a day. The dose may be increased slowly on alternate days until optimal blood pressure response is achieved;
• The usual dosage range is 20 to 40 mg twice or thrice daily.
• Doses of up to 240 mg per day have been reported.

phenoxybenzamine Dose in the treatment of Micturition disorders (off-label):

• Oral: 10 to 20 mg once or twice daily.

Phenoxybenzamine Dose in Childrens

phenoxybenzamine Dose in the preoperative management of Pheochromocytoma:

• Children and Adolescents:

  • Initial: 0.2 to 0.25 mg/kg/dose orally once or two times a day to a maximum dose of 10 mg/dose.
  • The dose is slowly titrated in increments of 0.2 mg/kg/day every fourth day until the effect is achieved.
  • The reported maintenance dose range is 0.4 to 3 mg/kg/day in divided doses every 6 to 8 hours;
  • The maximum single maintenance dose is 40 mg/dose.
  • The maximum daily dose is 4 mg/kg/day.

Pregnancy Risk Factor C

• It has not yet been tested in human or animal pregnancy studies.
• We don't know if it has any effect on the fetus, or on reproductive health.

Use during breastfeeding:

• It is unknown if the drug is excreted from breast milk.
• The drug could cause serious side effects in lactating children.
• Therefore, the manufacturer recommends that you either stop breastfeeding or weigh the risks and benefits of using the drug.

Dose in Kidney Disease:

There are no dosage adjustments provided in the manufacturer's labeling; use with caution.

Dose in Liver Disease:

There are no dosage adjustments provided in the manufacturer's labeling.

Side effects of phenoxybenzamine:

• Cardiovascular:

  • Orthostatic Hypotension
  • Tachycardia

• Central Nervous System:

  • Drowsiness
  • Fatigue
  • Inhibited Ejaculation

• Gastrointestinal:

  • Gastrointestinal Irritation

• Ophthalmic:

  • Miosis

• Respiratory:

  • Nasal Congestion

Contraindications to Phenoxybenzamine:

• Allergy reactions to the drug, or any component thereof;
• A blood pressure-lowering effect can be harmful in certain medical conditions.

Warnings and precautions

• Cardiovascular effects

  • When taken concurrently with drugs that stimulate the beta-adrenergic and alpha-adrenergic receptors, it can increase blood pressure and cause tachycardia.

• Cardiovascular disease

  • Patients with intracranial or coronary atherosclerosis should not use it.

• Renal impairment

  • Patients with impaired renal function should not use it.

• Respiratory infection

  • It can worsen the symptoms of respiratory infection.

Phenoxybenzamine: Drug Interaction

Note: Drug Interaction Categories:

• Risk Factor C: Monitor When Using Combination
• Risk Factor D: Consider Treatment Modification
• Risk Factor X: Avoid Concomitant Use

Monitoring Parameters:

• Blood pressure,
• pulse,
• Postural hypotension

How to administer Phenoxybenzamine?

It is administered orally without regard to meals, however, administration with milk may reduce the gastrointestinal side effects of the drug.

Mechanism of action of Phenoxybenzamine:

It is a non-competitive beta-adrenergic receptor blocking agent that blocks postganglionic neurotransmission in exocrine glands, smooth muscles of the bladder and urethra. This causes relaxation.

The beginning of action:

• Within 2 hours, the drug's effects are visible.
• Maximum effect can be seen in 4 to 6 hours

Time:

• Its effects can last up to four days if administered intravenously.

Distribution:

• It accumulates in the fatty tissues.

Bioavailability:

• 20% to 30%

Half-life elimination:

• It has a half-life elimination of about 24 hours.

Excretion:

• It is primarily excreted in urine and bile.

International Brand Names of Phenoxybenzamine:

• Dibenzyline
• Dibenzyran
• Fenoxene
• Lition
• Seton

Phenoxybenzamine Brand Names in Pakistan:

No Brands Available in Pakistan.