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Phenoxybenzamine
Each Dibenzyline capsule, with red cap and red body, is imprinted SKF and E33 and contains phenoxybenzamine hydrochloride, 10 mg. Inactive ingredients consist of benzyl alcohol, cetylpyridinium chloride, D&C Red No. 33, FD&C Red No. 3, FD&C Yellow No. 6, gelatin, lactose, sodium lauryl sulfate and trace amounts of other inactive ingredients. Dibenzyline is N-(2-Chloroethyl)-N-(1-methyl-2-phenoxyethyl)benzylamine hydrochloride. Phenoxybenzamine hydrochloride is a colorless, crystalline powder with
a molecular weight of 340.3 which melts between 136° and 141° C. It is
soluble in water, alcohol and chloroform; insoluble in ether.
Dibenzyline (phenoxybenzamine hydrochloride) is a long-acting, adrenergic, alpha-receptor blocking agent which can produce and maintain "chemical sympathectomy" by oral administration. It increases blood flow to the skin, mucosa and abdominal viscera, and lowers both supine and erect blood pressures. It has no effect on the parasympathetic system. Twenty to 30 percent of orally administered phenoxybenzamine appears to be absorbed in the active form.¹ The half-life of orally administered phenoxybenzamine hydrochloride is
not known; however, the half-life of intravenously administered drug is
approximately 24 hours. Demonstrable effects with intravenous administration
persist for at least 3 to 4 days, and the effects of daily administration
are cumulative for nearly a week.¹
Pheochromocytoma, to control episodes of hypertension and sweating. If tachycardia is excessive, it may be necessary to use a beta-blocking agent concomitantly.
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 Dibenzyline (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. HOW SUPPLIED Dibenzyline (phenoxybenzamine hydrochloride) capsules, 10 mg, in bottles of 100 (NDC 0007-3533-20). STORAGE Store between 15° and 30° C (59° and 86° F). REFERENCES 1. Weiner, N.: Drugs That Inhibit Adrenergic Nerves and Block Adrenergic Receptors, in Goodman, L. and Gilman, A., The Pharmacological Basis of Therapeutics, ed 6, New York, Macmillan Publishing Co., 1980, p. 179; p. 182. 2. Martin, E. W Drug Interactions Index 1978/1979,
Philadelphia, J. B. Lippincott Co., 1978, pp. 209-210.
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. Miscellaneous: Gastrointestinal irritation, drowsiness, fatigue. *These so-called "side effects" are actually evidence of adrenergic blockade and vary according to the degree of blockade.
Dibenzyline (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 WARNINGS.) Dibenzyline blocks hyperthermia production by levarterenol, and
blocks hypothermia production by reserpine.
Dibenzyline-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.
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 lnteractions ² Dibenzyline (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 Dibenzyline blocks hyperthermia production by levarterenol, and blocks hypothermia production by reserpine. Carcinogenesis, Mutagenesis, Impairment of Fertility Phenoxybenzamine hydrochloride has shown in vitro mutagenic activity in the Ames test and in the mouse lymphoma assay; it has not shown mutagenic activity in the micronucleus test in mice. In rats and mice repeated intraperitoneal administration of phenoxybenzamine hydrochloride resulted in peritoneal sarcomas. Chronic oral dosing in rats has produced malignant tumors in the gastrointestinal tract. The majority of these tumors were found in the nonglandular stomach of the rats. In chronic oral studies in rats, ulcerative and/or erosive gastritis of the glandular stomach occurred which was probably drug related. Pregnancy Teratogenic Effects - Pregnancy Category C. Adequate reproductive studies have not been performed with Dibenzyline (phenoxybenzamine hydrochloride). It is also not known whether Dibenzyline can cause fetal harm when administered to a pregnant woman. Dibenzyline should be given to a pregnant woman only if clearly needed. Nursing Mothers It is not known whether this drug 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 the drug, taking into account the importance of the drug to the mother. Pediatric Use Safety and effectiveness in pediatric patients have not been established.
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