HYDROXYZINE PAMOATE
Clinical safety rating: safe
CNS depressants may enhance sedative effects May cause marked drowsiness and QT prolongation.
Hydroxyzine pamoate is a piperazine derivative with antihistamine (H1 receptor antagonist) and anticholinergic properties. It also has sedative, anxiolytic, and antiemetic effects, likely mediated through suppression of subcortical regions of the central nervous system.
| Metabolism | Hydroxyzine is extensively metabolized in the liver primarily via CYP3A4 and CYP2D6 isoenzymes. The major metabolite is cetirizine, an active carboxylic acid metabolite. |
| Excretion | Primarily hepatic metabolism; <1% excreted unchanged in urine. Biliary/fecal elimination accounts for approximately 50% of metabolites. |
| Half-life | Terminal elimination half-life is approximately 20 hours (range 14-25 hours) in adults; may be prolonged in elderly or hepatic impairment. |
| Protein binding | Approximately 93% bound to plasma proteins, primarily albumin. |
| Volume of Distribution | Approximately 16 L/kg (range 13-20 L/kg); indicates extensive tissue distribution. |
| Bioavailability | Oral: approximately 100% (well absorbed); IM: approximately 100%. |
| Onset of Action | Oral: 15-30 minutes (antihistamine); 45-60 minutes (anxiolytic). IM: 15-30 minutes. |
| Duration of Action | Oral: 4-6 hours (antihistamine); 4-6 hours (anxiolytic). IM: 2-4 hours. Note: Sedative effects may persist longer. |
Oral: 50-100 mg every 6 hours as needed for pruritus or anxiety; maximum 600 mg/day. IM: 25-100 mg every 4-6 hours as needed.
| Dosage form | CAPSULE |
| Renal impairment | GFR 10-50 mL/min: Administer every 12 hours. GFR <10 mL/min: Administer every 24 hours or avoid use due to risk of accumulation. |
| Liver impairment | Child-Pugh A: No adjustment. Child-Pugh B: Reduce dose by 50%. Child-Pugh C: Use with caution; maximum 50 mg/day or avoid use. |
| Pediatric use | Oral: For pruritus: 0.5-1 mg/kg/dose every 6-8 hours. For anxiety: <6 years: 50 mg/day divided; ≥6 years: 50-100 mg/day divided. IM: 0.5-1 mg/kg/dose every 4-6 hours. |
| Geriatric use | Start at lower end of dosing range (25 mg orally) due to increased sensitivity and anticholinergic effects; caution with sedation and hypotension. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
CNS depressants may enhance sedative effects May cause marked drowsiness and QT prolongation.
| FDA category | Animal |
| Breastfeeding | Hydroxyzine is excreted in human breast milk; the milk-to-plasma ratio is not well established. The American Academy of Pediatrics considers hydroxyzine compatible with breastfeeding, but caution is advised due to potential for infant sedation and irritability. Monitor infant for drowsiness and feeding difficulties. |
| Teratogenic Risk |
■ FDA Black Box Warning
No FDA black box warning.
| Common Effects | pruritus |
| Serious Effects |
["Hypersensitivity to hydroxyzine or any component of the formulation","Early pregnancy (first trimester) due to potential fetal harm","Lactation (excreted in breast milk; contraindicated in nursing mothers)","Porphyria (may precipitate acute attacks)","Concomitant use with other CNS depressants may lead to additive sedation"]
| Precautions | ["May cause QT prolongation, especially in patients with risk factors (e.g., electrolyte abnormalities, concomitant QT-prolonging drugs).","Should be used with caution in elderly patients due to increased risk of anticholinergic effects and sedation.","May impair cognitive function and motor skills; patients should avoid driving or operating machinery until effects are known.","Use with caution in patients with hepatic impairment; dose adjustment may be required.","May increase the risk of seizures in patients with a history of seizure disorder."] |
Loading safety data…
| Hydroxyzine pamoate is classified as FDA Pregnancy Category C. Data in humans are limited; however, animal studies have shown teratogenic effects at high doses. There are no adequate and well-controlled studies in pregnant women. First trimester: Potential risk of fetal abnormalities cannot be ruled out; use only if clearly needed. Second and third trimesters: May cause neonatal respiratory depression, hypotonia, and withdrawal symptoms if used near term. |
| Fetal Monitoring | Monitor maternal vital signs, level of sedation, and signs of anticholinergic effects. For the fetus, assess fetal heart rate and movement patterns; if used near term, observe neonate for respiratory depression, hypotonia, and withdrawal symptoms. |
| Fertility Effects | Hydroxyzine has no known direct effects on human fertility. Animal studies have not shown impairment of fertility at therapeutic doses. However, its anticholinergic effects may theoretically affect sexual function; no specific data in humans. |