Xyzal
Cetirizine hydrochloride
Generic Name
Cetirizine hydrochloride
Mechanism
- Selective antagonist of peripheral histamine H1 receptors → blocks H1‑mediated vasodilation, vascular permeability, and smooth‑muscle contraction.
- Minimal central nervous system penetration → negligible blockade of brain H1 receptors → low sedation risk.
- Inhibits the degranulation of mast cells and basophils, reducing the release of histamine and other inflammatory mediators.
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Pharmacokinetics
| Parameter | Key Facts |
| Absorption | Rapid, bioavailability ~ 50 % (unchanged by food). |
| Onset | Peak plasma concentrations (tmax) ~ 1–2 h after oral dosing. |
| Metabolism | Primarily hepatic (CYP2D6, CYP3A4); minor metabolites are inactive. |
| Elimination | Renal excretion (about 65 % unchanged). Half‑life ~ 8–10 h in adults; longer (~18 h) in severe renal impairment. |
| Drug–Drug Interactions | Inhibits CYP3A4 and CYP2D6 → modest interactions with fluoxetine, quinidine, and high‑dose opioids. |
| Special Populations | Dose adjustment not required for mild‑to‑moderate hepatic disease; use caution in end‑stage renal disease. |
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Indications
- Seasonal allergic rhinitis (hay fever).
- Perennial allergic rhinitis.
- Chronic idiopathic urticaria (hives).
- Allergic conjunctivitis (when co‑administered with antihistamine eye drops).
- Adjunct for eczema when antihistamine benefit is desired.
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Contraindications
| Category | Note |
| Contraindications | Known hypersensitivity to cetirizine or any excipient. |
| Warnings |
• Rare reports of *QTc prolongation* in patients on multiple QT‑prolonging drugs. • Potential for *renal toxicity* in patients on nephrotoxic combinations (e.g., NSAIDs, cisplatin). • Not recommended during pregnancy unless no alternatives (Category C). |
| Precautions |
• Use caution in hepatic dysfunction; monitor aminotransferases. • In patients with *renal impairment*, start at the lowest effective dose and monitor trough levels. |
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Dosing
| Population | Dose | Frequency | Form |
| Adults (≥18 y) | 10 mg orally | Once daily (preferably in the evening or at bedtime) | Tablet, sachet, oral suspension |
| Children 6‑11 y | 5 mg orally | Once daily | Tablet, suspension |
| Children 1‑5 y | 2.5 mg orally | Once daily | Sachet, suspension |
| Pregnant or lactating women | 10 mg orally | Once daily | Same preparation |
| Renal impairment (CrCl 30–49 mL/min) | 5 mg orally | Once daily (if needed) | Same |
| End‑stage renal disease | 5 mg orally, then 5 mg every 12 h | Twice daily | Adjust to steady‑state. |
*Take with or without food; food does not significantly alter absorption.*
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Adverse Effects
| Category | Examples |
| Common (≤5 %) | Dry mouth, headache, fatigue, mild somnolence (rare due to second‑generation property). |
| Moderate (0.1–1 %) | Nausea, dizziness, constipation, blurred vision. |
| Rare (<0.1 %) | Rash, urticaria, angioedema (unlikely but possible), hypotension. |
| Serious (≤0.01 %) | QTc prolongation, severe hepatic dysfunction, anaphylactic reactions, significant bradycardia. |
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Monitoring
- Renal function: Serum creatinine & eGFR at baseline and periodically in patients ≥65 y or with comorbidities.
- Liver enzymes: ALT, AST, bilirubin if prolonged use (>6 months) or in patients with pre‑existing liver disease.
- Conduction intervals: QTc in patients on concurrent QT‑prolonging agents or with cardiac disease.
- Clinical efficacy & tolerability: Relief of allergic symptoms, adherence, and adverse reaction profile.
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Clinical Pearls
- “Take it with your evening routine.” The drug’s low sedative potential allows flexible timing, but bedtime dosing can maximize relief of nighttime symptoms.
- Avoid *caffeine”* with cetirizine – caffeine may offset the mild drowsiness of other H1 blockers, but when combined with cetirizine it can increase jitteriness in susceptible patients.
- Co‑administration with *quetiapine* or *fluoxetine” can elevate plasma levels due to CYP inhibition; watch for excessive sedation or hypotension.
- In pediatric patients (<6 y), a 2.5‑mg dose is effective and safe; a 5‑mg dose may be considered for severe urticaria under supervision.
- Sublingual delivery is not recommended; the tablet must be swallowed whole for optimal bioavailability.
- Use as first‑line in chronic idiopathic urticaria; if inadequate, add low‑dose montelukast for synergistic effect.
- No black‑box warning – unlike first‑generation antihistamines, cetirizine is safe for use in pregnancy and lactation when indicated.
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• Reference: UpToDate® Chapter on “Antihistamines in the Treatment of Allergic Rhinitis”, FDA prescribing information for Cetirizine Hydrochloride (Xyzal).