Hydroxyzine

First-generation antihistamine, Anxiolytic, Antipruritic, Sleep aid (off-label)

Hydroxyzine (hydrochloride; pamoate salt)

Vistaril (pamoate), Atarax (HCl, discontinued in US as brand)

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Summary

Classes

First-generation antihistamine, Anxiolytic, Antipruritic, Sleep aid (off-label)

Common uses

Anxiety symptoms (FDA, short-term)0, Pruritus from allergic conditions (FDA)0, Preoperative sedation (FDA)0, Nausea and vomiting (FDA, IM only)0, Insomnia (off-label)0, Acute alcohol withdrawal adjunct (off-label)0, Pediatric acute agitation (off-label)0

Pharmacy

Starting dose

Anxiety: 25-50 mg PO QID. Pruritus: 25 mg PO TID-QID. Insomnia: 25-50 mg PO at bedtime. Pediatric: 50-100 mg/day divided

Preparations

Tablets 10, 25, 50 mg (HCl); capsules 25, 50, 100 mg (pamoate); oral suspension 25 mg/5 mL; injection 25, 50 mg/mL (IM only, never IV)

US FDA Max

400 mg/day theoretical; in practice rarely exceeds 200 mg/day

Pharmacology

Routes

Oral, intramuscular

Onset

15-30 minutes (oral)

Duration

4-6 hours

Half-life

14-25 hours (longer in elderly and hepatic impairment)^[1]

Bioavailability

~80% (oral)^[1]

Pregnancy

Limited human data; older agent with substantial use experience; some signal for first-trimester exposure but not conclusive.^{[citation needed]}

Legal status

Rx-only in US. Not a controlled substance, which is a meaningful clinical advantage over the benzodiazepine alternatives for short-term anxiety^[1]

Purported mechanism

First-generation H1 histamine receptor antagonist with central nervous system penetration producing sedation. Additional 5-HT2A receptor antagonism, α1-adrenergic antagonism, and anticholinergic effects contribute to the sedative, anxiolytic, and antiemetic activity. Crucially, hydroxyzine has no GABA receptor activity, so it carries no tolerance to anxiolytic effect, no withdrawal syndrome, no dependence liability, and no controlled-substance status, distinguishing it sharply from the benzodiazepine alternatives.0 QT prolongation risk at high doses prompted the FDA's 2015 caution against use in patients with prolonged QT or with concurrent QT-prolonging medicines^[1].

References

↑ ^1.0 ^1.1 ^1.2 ^1.3 FDA Prescribing Information, Vistaril (hydroxyzine pamoate), Pfizer, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2009/011459s045lbl.pdf

[vistaril-label-1] 1.0 ^1.1 ^1.2 ^1.3 FDA Prescribing Information, Vistaril (hydroxyzine pamoate), Pfizer, current revision. https://www.accessdata.fda.gov/drugsatfda_docs/label/2009/011459s045lbl.pdf

[1]