Cetirizine
Zyrlex · Cetirizin Sandoz · Cetirizin Teva
First-line treatment for allergic rhinoconjunctivitis and chronic urticaria — one tablet daily, available without prescription, with good effect on itching, sneezing, and rhinorrhoea but weaker on nasal congestion. The critical difference from clemastine and promethazine is that cetirizine penetrates the blood-brain barrier poorly, but it is not entirely free of sedation: a distinct minority of patients become drowsy, and this should be asked about in professional drivers. Renal function governs the dose.
Cetirizine has no place in the acute treatment of anaphylaxis. Intramuscular adrenaline is the only treatment that affects the course — antihistamine relieves cutaneous and mucosal symptoms but neither raises blood pressure nor reverses bronchospasm, and must never delay administration of adrenaline.
Dosing in adults
| Indication | Regimen | Comment |
|---|---|---|
| Allergic rhinoconjunctivitis | 10 mg once daily | continuously during pollen season, not only when symptomatic |
| Chronic spontaneous urticaria | 10 mg once daily, with insufficient effect up to 40 mg daily | dose escalation above the approved dose according to guideline, on specialist indication |
| Acute urticaria and insect sting | 10 mg as a single dose, then as needed | symptom-relieving adjunct, not a substitute for adrenaline in systemic reaction |
| Children 6–12 years | 5 mg × 2 or 10 mg × 1 | oral drops or oral solution for younger children |
| Children 2–6 years | 2,5 mg × 2 (5 mg per day) | oral solution; not for children under 2 years |
eGFR 50–79 ml/min: 10 mg × 1. eGFR 30–49 ml/min: 5 mg × 1. eGFR 10–29 ml/min: 5 mg every other day. eGFR below 10 ml/min and haemodialysis: contraindicated — the substance is not removed by dialysis.
No dose adjustment in isolated hepatic failure. Reduce according to renal function if this is concurrently impaired.
From 2 years: 2,5 mg × 2. 6–12 years: 5 mg × 2 or 10 mg × 1. From 12 years adult dose 10 mg × 1.
Avoid relying on cetirizine in suspected anaphylaxis — this is the most dangerous trap with this drug. Also avoid the full dose at eGFR below 30 ml/min in the elderly; the accumulation that follows causes sedation and fall risk that can easily be misinterpreted as dementia progression or general frailty.
Pharmacokinetics
- ONSET
- 20–60 minutes
- PEAK CONCENTRATION
- approximately 1 hour
- DURATION
- over 24 hours
- t½
- approximately 10 hours (adults), 6 hours (children)
- PROTEIN BINDING
- 93 %
- METABOLISM
- Negligible — no significant CYP turnover
- EXCRETION
- Renal, approximately 2/3 unchanged
- CNS PENETRATION
- low, but not negligible