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Prudoxin (Doxepin Hydrochloride Topical) - Description and Clinical Pharmacology

 
 



FOR TOPICAL DERMATOLOGIC USE ONLY — NOT FOR OPHTHALMIC, ORAL, OR INTRAVAGINAL USE.

DESCRIPTION

PRUDOXIN (doxepin hydrochloride) Cream, 5% is a topical cream. Each gram contains: 50 mg of doxepin hydrochloride (equivalent to 44.3 mg of doxepin).

Doxepin hydrochloride is one of a class of agents known as dibenzoxepin tricyclic antidepressant compounds. It is an isomeric mixture of N,N-dimethyldibenz[b,e]oxepin-Δ11(6H),γ-propylamine hydrochloride. Doxepin hydrochloride has an empirical formula of C19H21NO•HCl and a molecular weight of 316.

PRUDOXIN Cream also contains sorbitol, cetyl alcohol, isopropyl myristate, glyceryl stearate, PEG-100 stearate, petrolatum, benzyl alcohol, titanium dioxide and purified water.

CLINICAL PHARMACOLOGY

Although doxepin HCl does have H1 and H2 histamine receptor blocking actions, the exact mechanism by which doxepin exerts its antipruritic effect is unknown. PRUDOXIN Cream can produce drowsiness which may reduce awareness, including awareness of pruritic symptoms. In 19 pruritic eczema patients treated with PRUDOXIN Cream, plasma doxepin concentrations ranged from nondetectable to 47 ng/mL from percutaneous absorption. Plasma levels from topical application of PRUDOXIN Cream can result in CNS and other systemic side effects.

Once absorbed into the systemic circulation, doxepin undergoes hepatic metabolism that results in conversion to pharmacologically-active desmethyldoxepin. Further glucuronidation results in urinary excretion of the parent drug and its metabolites. Desmethyldoxepin has a half-life that ranges from 28 to 52 hours and is not affected by multiple dosing. Plasma levels of both doxepin and desmethyldoxepin are highly variable and are poorly correlated with dosage. Wide distribution occurs in body tissues including lungs, heart, brain, and liver. Renal disease, genetic factors, age, and other medications affect the metabolism and subsequent elimination of doxepin. (See PRECAUTIONS - Drug Interactions.)

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