Molecule

Drug Groups

approved

Description

Doxepin hydrochloride is a dibenzoxepin-derivative tricyclic antidepressant (TCA). TCAs are structurally similar to phenothiazines. They contain a tricyclic ring system with an alkyl amine substituent on the central ring. In non-depressed individuals, doxepin does not affect mood or arousal, but may cause sedation. In depressed individuals, doxepin exerts a positive effect on mood. TCAs are potent inhibitors of serotonin and norepinephrine reuptake. Tertiary amine TCAs, such as doxepin and amitriptyline, are more potent inhibitors of serotonin reuptake than secondary amine TCAs, such as nortriptyline and desipramine. TCAs also down-regulate cerebral cortical β-adrenergic receptors and sensitize post-synaptic serotonergic receptors with chronic use. The antidepressant effects of TCAs are thought to be due to an overall increase in serotonergic neurotransmission. TCAs also block histamine H₁ receptors, α₁-adrenergic receptors and muscarinic receptors, which accounts for their sedative, hypotensive and anticholinergic effects (e.g. blurred vision, dry mouth, constipation, urinary retention), respectively. Doxepin has less sedative and anticholinergic effects than amitriptyline. See toxicity section below for a complete listing of side effects. Doxepin may be used to treat depression and insomnia. Unlabeled indications include chronic and neuropathic pain, and anxiety. Doxepin may also be used as a second line agent to treat idiopathic urticaria.

Indication

Labeled indications: depression and insomnia. Unlabeled indications: chronic and neuropathic pain, anxiety, idiopathic urticaria.

Pharmacology

Doxepin, a tricyclic antidepressant of the dibenzoxepin type, is used to treat depression and anxiety and, topically, pruritus associated with eczema. Doxepin has substantial anticholinergic and sedative effects.

Toxicity

LD₅₀=26 (mg/kg) (in mice, iv); LD₅₀=16 (mg/kg) (in rats, iv); Cardiac dysrhythmias, severe hypotension, convulsions, and CNS depression, including coma. Changes in the electrocardiogram, particularly in QRS axis or width, are clinically significant indicators of tricyclic antidepressant toxicity.
Side effects include: sedation, hypotension, blurred vision, dry mouth, constipation, urinary retention, postural hypotension, tachycardia, hypertension, ECG changes, heart failure, impaired memory and delirium, and precipitation of hypomanic or manic episodes in bipolar depression.
Withdrawal symptoms include gastrointestinal disturbances, anxiety, and insomnia.

Affected Organisms

Biotransformation

Extensively metabolized in the liver via the same pathways as other TCAs. N-demethylation produces an active metabolite, N-desmethyldoxepin.

Absorption

Well-absorbed from the GI tract. Peak plasma concentrations occur within 2 hours of oral administration.

Half Life

6 - 24.5 hours

Protein Binding

Highly bound to plasma proteins.

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