VISTARIL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for VISTARIL (VISTARIL).
Hydroxyzine is a piperazine derivative antihistamine that acts as a competitive antagonist of histamine H1 receptors, thereby suppressing histamine activity in the subcortical area of the central nervous system. It also has anxiolytic, sedative, antiemetic, and antispasmodic effects.
| Metabolism | Primarily hepatic via CYP3A4 and CYP2D6; major metabolites include cetirizine. |
| Excretion | Primarily hepatic metabolism; <1% excreted unchanged in urine; biliary/fecal elimination of metabolites accounts for approximately 50-60% of total clearance. |
| Half-life | Terminal elimination half-life: 20-25 hours in adults; prolonged in hepatic impairment or elderly; steady-state achieved in ~4-5 days. |
| Protein binding | Highly protein-bound: approximately 89-93%, primarily to albumin. |
| Volume of Distribution | Volume of distribution: 7-10 L/kg, indicating extensive tissue distribution. |
| Bioavailability | Oral: incomplete bioavailability due to first-pass metabolism, estimated at 40-60%; IM: nearly complete (85-100%). |
| Onset of Action | Oral: 15-30 minutes; IM: 15-30 minutes; IV: within 5 minutes. |
| Duration of Action | Oral: 4-6 hours (anxiolytic), 24 hours (antihistamine); IM/IV: 4-6 hours (anxiolytic/sedative). |
Oral: 50-100 mg 4 times daily; IM: 25-100 mg every 4-6 hours as needed.
| Dosage form | CAPSULE |
| Renal impairment | No specific adjustment; use with caution in severe renal impairment due to potential accumulation of metabolites. |
| Liver impairment | Child-Pugh Class A: no adjustment; Child-Pugh Class B: reduce dose by 50%; Child-Pugh Class C: avoid use. |
| Pediatric use | Oral: 0.5-1 mg/kg every 4-6 hours; maximum 50 mg per dose (≤12 years); IM: 0.5-1 mg/kg every 4-6 hours. |
| Geriatric use | Start at lower end of dosing range (e.g., 25 mg oral 3-4 times daily); monitor for sedation and anticholinergic effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for VISTARIL (VISTARIL).
| Breastfeeding | Hydroxyzine is excreted in human milk; M/P ratio not established. Potential for adverse effects in infants (sedation, irritability). Use during breastfeeding only if clearly needed; monitor infant for drowsiness. |
| Teratogenic Risk | First trimester: Limited human data; animal studies suggest no major teratogenic risk; fetal harm cannot be ruled out. Second and third trimesters: Hydroxyzine may cause neonatal withdrawal symptoms (irritability, tremors) with chronic maternal use near term; no evidence of structural anomalies. |
■ FDA Black Box Warning
No FDA black box warning.
| Serious Effects |
["Hypersensitivity to hydroxyzine or any component","Early pregnancy (first trimester)","Porphyria","Breastfeeding (use caution)"]
| Precautions | ["May cause QT prolongation; use with caution in patients with risk factors (e.g., electrolyte imbalance, concomitant QT-prolonging drugs)","Sedation and impaired cognitive/motor function; avoid driving or hazardous activities","Anticholinergic effects (e.g., urinary retention, constipation); use cautiously in elderly or patients with prostatic hypertrophy","Respiratory depression with concurrent CNS depressants","Use in pregnancy: avoid especially during early pregnancy; may increase risk of fetal abnormalities"] |
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| Fetal Monitoring |
| Monitor maternal vital signs and level of sedation; assess fetal heart rate and uterine activity if used during labor; observe neonate for respiratory depression and withdrawal symptoms after delivery. |
| Fertility Effects | No specific studies on human fertility; animal studies show no significant reproductive impairment at clinically relevant doses. |