Doxepin
(Redirected from Silenor)
Tricyclic antidepressant (TCA), Antidepressant, Sleep aid (Silenor low-dose), Antihistamine (potent H1)
Doxepin (hydrochloride)
Sinequan (oral antidepressant, US brand discontinued), Silenor (low-dose for insomnia), Prudoxin / Zonalon (topical cream)
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Summary
Classes
Common uses
Major depressive disorder (FDA, oral antidepressant dose)0, Anxiety disorders (FDA)0, Insomnia, sleep maintenance type (Silenor 3-6 mg, FDA)0, Chronic urticaria and pruritus (off-label, leveraging H1 antihistamine activity)0, Topical treatment of localized pruritus (Prudoxin 5% cream, FDA)0
Pharmacy
Starting dose
Depression: 25-75 mg/day to start, titrate to 75-150 mg/day at bedtime. Insomnia (Silenor): 3 mg PO 30 minutes before bedtime, max 6 mg. Topical (Prudoxin): apply to affected area every 3-4 hours
Preparations
Capsules 10, 25, 50, 75, 100, 150 mg; oral concentrate 10 mg/mL; Silenor tablets 3, 6 mg; topical cream 5% (Prudoxin, Zonalon)
US FDA Max
300 mg/day (depression, hospitalized); 150 mg/day outpatient; 6 mg/day for insomnia
Pharmacology
Routes
Oral, topical
Onset
Sleep effect from first dose; antidepressant effect over 1-4 weeks
Duration
24 hours (HS dosing)
Half-life
~15 hours (parent); nordoxepin active metabolite ~30 hours[2]
Bioavailability
~30% (oral)[2]
Pregnancy
TCA class signal; limited human data specific to doxepin.[citation needed]
Legal status
Purported mechanism
Tricyclic antidepressant with the strongest H1 antihistamine activity of any TCA, actually the most potent H1 antihistamine in clinical use, exceeding diphenhydramine on a molar basis. This is why low-dose doxepin (Silenor 3-6 mg) is uniquely sedating without anticholinergic burden at low doses: the H1 effect saturates at very low concentrations, while the muscarinic and α-adrenergic effects do not contribute meaningfully until higher antidepressant doses (75-300 mg).0 At antidepressant doses, the standard TCA mechanisms apply: serotonin and norepinephrine reuptake inhibition, anticholinergic, antihistaminergic, and α1-adrenergic antagonism. CYP2D6 and CYP2C19 substrate; CPIC TCA dosing guidance applies[1].
References
- ↑ CPIC Guideline for CYP2D6 and CYP2C19 Genotypes and Dosing of Tricyclic Antidepressants, 2016. https://cpicpgx.org/guidelines/guideline-for-tricyclic-antidepressants-and-cyp2d6-and-cyp2c19/
- ↑ 2.0 2.1 2.2 FDA Prescribing Information, Silenor (doxepin tablets), Pernix/Currax, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2010/022036lbl.pdf