PHENOXYBENZAMINE: 52 Adverse Event Reports & Safety Profile

DESCRIPTION Each phenoxybenzamine hydrochloride capsule, USP with red cap and body, is imprinted with “Amneal” on cap and “1502” on body, and contains 10 mg of phenoxybenzamine hydrochloride, USP. Inactive ingredients consist of colloidal silicon dioxide, D&C red 33, FD & C red 3, gelatin, iron oxide yellow, lactose monohydrate and sodium lauryl sulfate. The capsule is imprinted with white pharmaceutical ink which contains butyl alcohol, dehydrated alcohol, isopropyl alcohol, potassium hydroxide, propylene glycol, shellac, strong ammonia solution and titanium dioxide. Phenoxybenzamine hydrochloride is chemically known as N-(2-Chloroethyl)-N-(1-methyl-2-phenoxyethyl) benzylamine hydrochloride. Its molecular formula is C 18 H 22 ClNO·HCl. The chemical structure is: Phenoxybenzamine hydrochloride, USP is a white to almost white crystalline powder with a molecular weight of 340.29 g/mol, which melts between 136° and 141°C. It is freely soluble in ethanol (96%) and insoluble in diethyl ether. FDA approved organic impurity specification differs from the USP. 1

INDICATION AND USAGE Phenoxybenzamine hydrochloride capsules are indicated in the treatment of pheochromocytoma, to control episodes of hypertension and sweating. If tachycardia is excessive, it may be necessary to use a beta -blocking agent concomitantly.

DOSAGE AND ADMINISTRATION The dosage should be adjusted to fit the needs of each patient. Small initial doses should be slowly increased until the desired effect is obtained or the side effects from blockade become troublesome. After each increase, the patient should be observed on that level before instituting another increase . The dosage should be carried to a point where symptomatic relief and/or objective improvement are obtained, but not so high that the side effects from blockade become troublesome. Initially, 10 mg of phenoxybenzamine hydrochloride twice a day. Dosage should be increased every other day, usually to 20 to 40 mg 2 or 3 times a day, until an optimal dosage is obtained, as judged by blood pressure control. Long-term use of phenoxybenzamine is not recommended (see PRECAUTIONS Carcinogenesis and Mutagenesis ).

Storage

Store at 20° to 25°C (68° to 77°F) [see USP Controlled Room Temperature]. Dispense in a tight container.

CONTRAINDICATIONS Conditions where a fall in blood pressure may be undesirable; hypersensitivity to the phenoxybenzamine hydrochloride capsules, or any of its components.

ADVERSE REACTIONS 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. To report SUSPECTED ADVERSE REACTIONS, contact Aurobindo Pharma USA, Inc. at 1-866-850-2876 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

WARNINGS Phenoxybenzamine hydrochloride-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.

PRECAUTIONS General–Administer with caution in patients with marked cerebral or coronary arteriosclerosis or renal damage. Adrenergic blocking effect may aggravate symptoms of respiratory infections.

Drug Interactions

2 – Phenoxybenzamine hydrochloride may interact with compounds that stimulate both alpha- and beta- adrenergic receptors (i.e. epinephrine) to produce an exaggerated hypotensive response and tachycardia (see WARNING ). Phenoxybenzamine hydrochloride blocks hyperthermia production by levarterenol, and blocks hypothermia production by reserpine. Carcinogenesis and Mutagenesis Case reports of carcinoma in humans after long-term treatment with phenoxybenzamine have been reported. Hence long-term use of phenoxybenzamine is not recommended 3, 4 . Carefully weigh the benefits and risks before prescribing phenoxybenzamine hydrochloride. Phenoxybenzamine hydrochloride showed in vitro mutagenic activity in the Ames test and mouse lymphoma assay; it did not show mutagenic activity in vivo in the micronucleus test in mice. In rats and mice, repeated intraperitoneal administration of phenoxybenzamine hydrochloride (three times per week for up to 52 weeks) resulted in peritoneal sarcomas. Chronic oral dosing in rats (for up to 2 years) produced malignant tumors of the small intestine and non-glandular stomach, as well as ulcerative and/or erosive gastritis of the glandular stomach. Whereas squamous cell carcinomas of the non-glandular stomach were observed at all tested doses of phenoxybenzamine hydrochloride, there was a no-observed-effect-level of 10 mg/kg for tumors (carcinomas and sarcomas) of the small intestine. This dose is, on a body surface area basis, about twice the maximum recommended human dosage of 20 mg b.i.d. Pregnancy - Teratogenic Effects Adequate reproductive studies in animals have not been performed with phenoxybenzamine hydrochloride. It is also not known whether phenoxybenzamine hydrochloride can cause fetal harm when administered to a pregnant woman. Phenoxybenzamine hydrochloride should be given to a pregnant woman only if clearly needed.

Nursing

Mothers It is not known whether phenoxybenzamine hydrochloride is excreted in human milk. Because many drugs are excreted in human milk, and because of the potential for serious adverse reactions from phenoxybenzamine hydrochloride, a decision should be made whether to discontinue nursing or to discontinue phenoxybenzamine hydrochloride, taking into account the importance of the drug to the mother.

Pediatric Use

Safety and effectiveness in pediatric patients have not been established.

Drug Interactions 2 – Phenoxybenzamine hydrochloride may interact with compounds that stimulate both alpha- and beta- adrenergic receptors (i.e. epinephrine) to produce an exaggerated hypotensive response and tachycardia (see WARNING ). Phenoxybenzamine hydrochloride blocks hyperthermia production by levarterenol, and blocks hypothermia production by reserpine.