Generic Name

Atarax

Mechanism

• Histamine H₁‑receptor antagonism: blocks peripheral postsynaptic H₁ receptors, leading to reduced pruritus, vasodilatation, and uterine relaxation.
• Central nervous system (CNS) sedation: hydroxyzine crosses the blood‑brain barrier and exerts central H₁ blockade, producing anxiolytic and hypnotic effects.
• Anticholinergic activity: modest inhibition of muscarinic receptors → dry mouth, blurred vision, constipation.
• Neutralization of mast‑cell mediator release: reduces histamine and polypeptide release, beneficial in allergic inflammation.

Pharmacokinetics

• Absorption: oral bioavailability ~85 % (rapid, peak plasma concentration within 1–3 h).
• Distribution: extensive tissue distribution, high protein binding (~86 % to albumin).
• Metabolism: hepatic N‑demethylation → primarily inactive metabolites; minimal CYP involvement.
• Elimination: renal excretion (~80 % as metabolites); mean elimination half‑life 20–25 h (single dose). Renal impairment prolongs half‑life.
• Special Populations:
• Geriatric: increased sensitivity; consider starting lower dose.
• Hepatic/Cirrhosis: no dosage adjustment needed (low hepatic metabolism).
• Renal: reduce dose or defer dosing if CrCl <30 mL/min.

Indications

• Anxiety (short‑term adjunctive treatment).
• Premedication for sedation in minor procedures or to manage agitation.
• Allergic conditions: urticaria, pruritus, and allergic rhinitis.
• Nausea & vomiting (antiemetic).
• Adjunctive therapy in management of atopic dermatitis when topical agents insufficient.

Contraindications

• Contraindications:
• Known hypersensitivity to hydroxyzine or phenothiazine derivatives.
• Severe hepatic disease (rare).
• Ocular hypertension or narrow‑angle glaucoma (risk of intra‑ocular pressure rise).
• Warnings:
• Central anticholinergic toxicity in high doses or with CNS‑acting drugs.
• QT prolongation: avoid in patients with pre‑existing QT disorders or when co‑prescribed with drugs that prolong QT.
• Sedation: risk of falls in elderly; advise against driving or operating machinery.
• Pregnancy: category B; use with caution, only if benefit outweighs risk.
• Breastfeeding: excreted in milk—consider alternative when possible.

Dosing

• Adults: 25 mg orally every 4–6 h as needed (max 200 mg/day).
• Children (≥12 yrs): 10–25 mg orally every 4–6 h (max 100 mg/day).
• Pregnancy: 25 mg PO 2–3×/day adequate for anxiety; no evidence of teratogenicity.
• Renal impairment (CrCl 30–50 mL/min): 25 mg every 8 h.
• Elderly: start with 10 mg PO once; titrate as needed.
• Intravenous (rarely used): 50 mg IV over 5 min, repeat as needed; monitor for hypotension.

Adverse Effects

• Common
• Somnolence, dizziness, mental dullness.
• Dry mouth, blurred vision, urinary retention.
• Headache, mild ataxia.
• Serious
• Anticholinergic crisis (severe CNS depression, hyperthermia, seizures).
• Paradoxical agitation or anxiety in some patients.
• QT‑interval prolongation → torsades de pointes (rare).
• Severe allergic reactions (anaphylaxis) with rare immediate hypersensitivity.

Monitoring

• Vital signs: pulse, BP, and respiration noted before dosing in high‑risk scenarios.
• Neurologic: monitor consciousness, especially in elderly or those receiving CNS agents.
• Cardiac: assess baseline ECG in patients with known QT prolongation; repeat if symptomatic.
• Renal: creatinine clearance assessment in renal‑impaired patients for dose titration.
• Patient counselling: on potential for sedation, handling of muscarinic side‑effects, and avoidance of alcohol or CNS depressants.

Clinical Pearls

• Drug Interactions: synergistic CNS depression when combined with opioids, benzodiazepines, or alcohol. Avoid or titrate proactively.
• Cardiovascular use: hydroxyzine can mask palpitations; monitor carefully in patients with arrhythmias.
• Pre‑operative adjunct: can reduce pre‑operative anxiety and facilitate intubation; dose 25 mg 30 min pre‑op.
• Dry Mouth & Dental Health: prescribe over‑the‑counter saliva substitutes or anticholinergic‑free hyaluronic acid gel to prevent xerostomia‑related complications.
• Alternative indications: hydroxyzine’s anxiolytic effect is beneficial in sleep disorders; a single 50 mg dose may improve sleep quality in short-term use.
• Contra‑Indication Detective: check for narrow‑angle glaucoma or ocular hypertension before commencing Atarax; consider screening with slit‑lamp exam if history unclear.
• Drug‑Loading: a brief 12‑h loading of 50 mg per day is sometimes used for severe pruritus, but watch for cumulative sedation.

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• Key pharmacology terms: *hydroxyzine*, *first‑generation antihistamine*, *H₁ antagonist*, *anticholinergic*, *QT prolongation*, *anxiety*, *pruritus*, *ulnar*, *renally cleared*.

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• For further updates and evidence‑based dosage recommendations, refer to the latest FDA prescribing information and peer‑reviewed pharmacology texts.