Dibenzyline

Phenoxybenzamine comes as a capsule to take by mouth. It usually is taken two or three times a day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take phenoxybenzamine exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Phenoxybenzamine controls symptoms related to pheochromocytoma and controls bladder symptoms but does not cure them. Continue to take phenoxybenzamine even if you feel well. Do not stop taking phenoxybenzamine without talking to your doctor.

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Stop using phenoxybenzamine and call your doctor at once if you severe dizziness or if you feel like you might pass out.

Less serious side effects may include:

• stuffy nose;
• mild dizziness or drowsiness;
• blurred vision;
• trouble having an orgasm;
• upset stomach; or
• tired feeling.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Dibenzyline (phenoxybenzamine) -induced alpha-adrenergic blockade leaves beta-adrenergic receptors unopposed. Compounds that stimulate both types of receptors may, therefore, produce an exaggerated hypotensive response and tachycardia.

Phenoxybenzamine lowers blood pressure.

Phenoxybenzamine is used control blood pressure and reduce sweating in people with pheochromocytoma.

Phenoxybenzamine may also be used for other purposes not listed in this medication guide.

This medication can cause side effects that may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be awake and alert.

Avoid getting up too fast from a sitting or lying position, or you may feel dizzy. Get up slowly and steady yourself to prevent a fall.

Avoid drinking alcohol. It can increase drowsiness caused by phenoxybenzamine.

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Stop using phenoxybenzamine and call your doctor at once if you severe dizziness or if you feel like you might pass out.

Less serious side effects may include:

• stuffy nose;

• mild dizziness or drowsiness;

• blurred vision;

• trouble having an orgasm;

• upset stomach; or

• tired feeling.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Pheochromocytoma

Prevention or treatment of paroxysmal hypertension and sweating in patients with pheochromocytoma.a b

Considered drug of choice for medical management of pheochromocytoma until surgery is performed and for prolonged treatment of hypertension caused by pheochromocytoma notamenable to surgery.a

Used in conjunction with a β-adrenergic blocking agent (propranolol) to control symptoms from excessive β-receptor stimulation in patients with inoperable or metastatic pheochromocytoma or to control tachycardia prior to or during pheochromocytomectomy.a b (See General under Dosage and Administration.)

Peripheral Vascular Diseases

Has been used as adjunctive therapy in the treatment of peripheral vasospastic disorders associated with increased α-adrenergic activity† (e.g., Raynaud’s syndrome, acrocyanosis, and frostbite sequelae) but efficacy in the treatment of peripheral vascular disease is not established.a

Phenoxybenzamine should not be used in diseases affecting large blood vessels.a

Micturition Disorders and Urinary Retention

Has been used in the treatment of micturition disorders† resulting from neurogenic bladder,100 functional outlet obstruction,100 or partial prostatic obstruction.100 101 102 103

Has been used for the prevention and treatment of acute postoperative urinary retention†,105 106 107 108 including that associated with the use of epidural morphine.107 108

• Long-acting, α-adrenergic blocking agent that produces and maintains chemical sympathectomy.b

• Inhibits responses (primarily excitatory responses of smooth muscle and exocrine glands) to adrenergic stimuli by noncompetitively blocking α-adrenergic receptors; however, does not affect β-adrenergic receptorsa or the parasympathetic system.b

• Exact mechanism of action not fully elucidated; appears to form a reactive ethylenimonium intermediate and a highly reactive carbonium ion that forms stable covalent bonds with sulfhydryl, phosphate, amino, and carboxyl groups of α-adrenergic receptors.a

• Blocks α-adrenergic responses to circulating epinephrine and/or norepinephrine and to norepinephrine released at the adrenergic nerve ending.a

• Acts on vascular smooth muscle to block epinephrine- and norepinephrine-induced vasoconstriction and causes peripheral vasodilation and reflex tachycardia.a Reverses the pressor effect of epinephrine (“epinephrine reversal”) and blocks, but does not reverse, the vasoconstrictor effects of norepinephrine.a

• Increases blood flow to the skin, mucosa, and abdominal viscera; lowers BP;b blocks pupillary dilation, lid retraction, and adrenergically mediated sweating; and decreases uterine motility.a

The following adverse reactions have been observed, but there are insufficient data to support an estimate of their frequency.

Autonomic Nervous System*: Postural hypotension, tachycardia, inhibition of ejaculation, nasal congestion, miosis.

*These so-called "side effects" are actually evidence of adrenergic blockade and vary according to the degree of blockade.

Miscellaneous: Gastrointestinal irritation, drowsiness, fatigue.

SYMPTOMS − These are largely the result of blocking of the sympathetic nervous system and of the circulating epinephrine. They may include postural hypotension, resulting in dizziness or fainting; tachycardia, particularly postural; vomiting; lethargy; shock.

Applies to phenoxybenzamine: oral capsule

In rats and mice, phenoxybenzamine (the active ingredient contained in Dibenzyline) has been found to increase the risk of development of malignant tumors. It is not known if phenoxybenzamine increases the chance of tumors in humans.

Along with its needed effects, phenoxybenzamine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Some side effects of phenoxybenzamine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

• Dizziness or lightheadedness, especially when getting up from a lying or sitting position
• fast heartbeat
• pinpoint pupils
• stuffy nose

• Confusion
• drowsiness
• dryness of mouth
• headache
• lack of energy
• sexual problems in males
• unusual tiredness or weakness

Applies to phenoxybenzamine: compounding powder, oral capsule

Cardiovascular

Cardiovascular side effects have included postural hypotension and tachycardia. These symptoms are evidence of adrenergic blockade and vary according to the degree of blockade.[Ref]

Genitourinary

Genitourinary side effects have included inhibition of ejaculation. This symptom is indicative of adrenergic blockade and varies according to the degree of blockade.[Ref]

Respiratory

Respiratory side effects have included nasal congestion. This symptom is indicative of adrenergic blockade and varies according to the degree of blockade.[Ref]

Ocular

Ocular side effects have included miosis. This symptom is indicative of adrenergic blockade and varies according to the degree of blockade.[Ref]

Nervous system

Nervous system side effects have included drowsiness and fatigue.[Ref]

Gastrointestinal

Gastrointestinal side effects have included gastrointestinal irritation.[Ref]

Some side effects of Dibenzyline may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.