Vistaril
Vistaril
Generic Name
Vistaril
Mechanism
Hydroxyzine, the active ingredient in Vistaril, is a *first‑generation H1‑histamine receptor antagonist* with significant anticholinergic properties.
• H1 Blockade:
• Prevents histamine binding → ↓ CNS arousal, ↓ peripheral vasodilation, ↓ smooth‑muscle contraction.
• Contributes to its anti‑pruritic, anxiolytic, and sedative effects.
• Anticholinergic Activity:
• Blocks muscarinic M1–M5 receptors → ↓ secretions, ↓ GI motility, ↑ blood pressure in the short term.
• Additional Actions:
• Mild dopaminergic antagonism (minor extrapyramidal effects).
• Potentiates benzodiazepines and alcohol; may cause additive CNS depression.
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Pharmacokinetics
| Parameter | Detail |
| Absorption | Rapid oral absorption; peak plasma concentrations in 1–2 h. |
| Bioavailability | ~70 % (first‑pass metabolism). |
| Protein Binding | Low (~10 %). |
| Metabolism | Hepatic N‑demethylation → primarily 1‑hydroxyhydroxyzine (active). |
| Half‑Life | 20–30 h (oral), 7–8 h (IV). Prolonged in elderly or hepatic impairment. |
| Elimination | Primarily renal (≈85 %)—reduced in renal failure; dose adjustment usually not needed for mild–moderate impairment. |
| Drug Interactions | CYP2D6 substrates; avoid strong CYP2D6 inhibitors (e.g., fluoxetine). |
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Indications
- Acute anxiety: short‑term symptomatic relief.
- Pre‑operative anxiolysis: sedation before surgery.
- Pruritus: urticaria, atopic dermatitis, neuropathic itch.
- Allergic reactions: urticaria, angioedema.
- Anti‑emetic prophylaxis: prevents nausea/vomiting secondary to anesthetics.
- Sedation in palliative care: calming agitation.
- Adjunct in acute psychosis: when benzodiazepines inadequate.
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Contraindications
| Category | Precautions |
| Contraindicated |
• Severe hypersensitivity to hydroxyzine or phenothiazines. • Acute angle‑closure glaucoma. • Severe hepatic or renal impairment? (Generally safe but cautious). • Pregnancy category B – avoid if possible. |
| Use with Caution |
• Elderly patients (increased anticholinergic burden). • Children <12 y (drowsiness, seizures). • Patients on MAO‑I (risk of serotonin syndrome). • Concomitant CNS depressants (benzodiazepines, opioids, alcohol). |
| Warnings |
• QT prolongation (especially >400 ms). • Severe dry mouth, blurred vision, urinary retention. • Paradoxical excitement or agitation in adolescents. |
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Dosing
| Indication | Adult Dose | Pediatric (2–12 y) | Notes |
| Acute Anxiety | 25–100 mg PO q6–8 h; max 400 mg/day | 0.5–1 mg/kg (max 25 mg) PO q6–8 h | Titrate to effect. |
| Pre‑op Sedation | 25–50 mg PO 1–2 h pre‑op | 0.5–1 mg/kg PO 1 h pre‑op | Avoid in severe hepatic dysfunction. |
| Pruritus/Allergy | 25–100 mg PO q6–8 h; max 400 mg/day | 0.5–1 mg/kg PO | 4 h intervals for acute itch. |
| Anti‑emetic | 20–40 mg IV q6–8 h | – | 4 h intervals. |
| Adjunct Sedation | 25–75 mg PO q6–8 h | – | Use lowest dose; monitor sedation. |
IV Formulation: 20–40 mg q6–8 h; infusion over 5–10 min.
Route: Oral or IV. Oral tablets (25 mg, 50 mg, 100 mg). No topical formulation in U.S.
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Adverse Effects
| Category | Examples |
| Common | Drowsiness, dry mouth, blurred vision, constipation, mild headache. |
| Serious | Severe anticholinergic syndrome (delirium, tachycardia, urinary retention), respiratory depression when co‑administered with opioids, QTc prolongation, seizures (rare), paradoxical agitation. |
| Risk Factors | Elderly, renal/hepatic impairment, CNS depressant co‑use. |
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Monitoring
- ECG: baseline and follow‑up if therapy >1 week or QTc >450 ms.
- Blood Pressure & Pulse: baseline; monitor for orthostatic hypotension.
- Renal & Hepatic Function: baseline in chronic use or suspected impairment.
- Mental Status: particularly in geriatrics; assess for delirium.
- Signs of Anticholinergic Toxicity: delirium, hallucinations, urinary retention.
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Clinical Pearls
| Pearl | Explanation |
| Use the lowest effective dose | Hydroxyzine’s therapeutic window is narrow; higher doses mainly increase sedation/anticholinergic burden without added anxiety benefit. |
| Avoid alcohol and CYP2D6 inhibitors | Alcohol or medications like fluoxetine can potentiate CNS depression and prolong half‑life. |
| Screen for QTc prolongation | Particularly in patients on other QT‑prolonging drugs (e.g., ondansetron). |
| Consider topical antihistamines for localized pruritus | Avoid systemic hydroxyzine if pruritus is confined; reduces side‑effect risk. |
| Beware of paradoxical agitation in children and adolescents | Might occur even at low doses; switch to non‑sedating antihistamine or benzodiazepine if needed. |
| Use with caution post‑operatively | Over‑sedation can mask airway obstruction in patients with respiratory compromise. |
| Hydroxyzine in palliative care | Helpful for agitation, sleep deprivation, and pruritus; often preferred over benzodiazepines due to shorter CNS effects. |
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• Key Takeaway:
Vistaril (hydroxyzine) is a versatile, first‑generation antihistamine with potent anxiolytic, sedative, and anticholinergic actions. It remains a go‑to therapy for acute anxiety, pre‑operative sedation, and pruritus when used judiciously, keeping in mind its anticholinergic side‑effect profile and QTc‑prolongation risk.