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Doxepin (Doxepin Hydrochloride) - Description and Clinical Pharmacology

 
 



DESCRIPTION SECTION

Doxepin hydrochloride is one of a class of psychotherapeutic agents known as dibenzoxepin tricyclic compounds. The molecular formula of the compound is C19H21NO • HCl having a molecular weight of 316. It is a white crystalline solid readily soluble in water, lower alcohols and chloroform. It may be represented by the following structural formula:

Chemically, doxepin hydrochloride is a dibenzoxepin derivative and is the first of a family of tricyclic psychotherapeutic agents. Specifically, it is an isomeric mixture of 1-Propanamine, 3-dibenz[b,e]oxepin-11 (6H)ylidene-N,N-dimethyl-hydrochloride.

Each 10 mg, 25 mg, 50 mg, 75 mg and 100 mg doxepin capsule for oral administration contains doxepin hydrochloride, USP equivalent to 10 mg, 25 mg, 50 mg, 75 mg and 100 mg of doxepin, respectively and the following inactive ingredients: colloidal silicon dioxide, magnesium stearate, microcrystalline cellulose, pregelatinized starch (corn) and sodium lauryl sulfate. The empty gelatin capsule shells contain D&C Yellow No. 10, gelatin, sodium lauryl sulfate and titanium dioxide. In addition, the 10 mg, 25 mg and 50 mg empty gelatin capsule shells contain FD&C Yellow No. 6 and the 75 mg and 100 mg empty gelatin capsule shells contain FD&C Green No. 3.

The imprinting ink contains black iron oxide, D&C Yellow No. 10 Aluminum Lake, FD&C Blue No. 1 Aluminum Lake, FD&C Blue No. 2 Aluminum Lake, FD&C Red No. 40 Aluminum Lake, propylene glycol and shellac glaze.

CLINICAL PHARMACOLOGY SECTION

The mechanism of action of doxepin is not definitely known. It is not a central nervous system stimulant nor a monoamine oxidase inhibitor. The current hypothesis is that the clinical effects are due, at least in part, to influences on the adrenergic activity at the synapses so that deactivation of norepinephrine by reuptake into the nerve terminals is prevented. Animal studies suggest that doxepin does not appreciably antagonize the antihypertensive action of guanethidine. In animal studies anticholinergic, antiserotonin and antihistamine effects on smooth muscle have been demonstrated. At higher than usual clinical doses norepinephrine response was potentiated in animals. This effect was not demonstrated in humans.

At clinical dosages up to 150 mg per day, doxepin can be given to man concomitantly with guanethidine and related compounds without blocking the antihypertensive effect. At dosages above 150 mg per day blocking of the antihypertensive effect of these compounds has been reported.

Doxepin is virtually devoid of euphoria as a side effect. Characteristic of this type of compound, doxepin has not been demonstrated to produce the physical tolerance or psychological dependence associated with addictive compounds.

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