Antihistamines 🤧
Reference guide for antihistamines (Zirtek, Clarityn, Telfast, Neoclarityn, Piriton, Phenergan). Drug table by sedating vs non-sedating, doses, and Irish SmPC links.
💡 Overview
- Antihistamines (H₁ blockers) treat allergic rhinitis (hay fever), urticaria, and itch.
- Prefer non-sedating agents for daytime use (cetirizine, loratadine, fexofenadine, desloratadine).
- Sedating agents (chlorphenamine, promethazine) help itch at night but increase falls/delirium risk — avoid in elderly where possible.
📋 Ward considerations
- Hold sedating antihistamines in delirium, falls risk, glaucoma, or significant prostatic symptoms.
- Cetirizine: dose-reduce in renal impairment; can still cause mild drowsiness.
- Stop antihistamines 3 days before allergy skin testing (wash-out).
- IV/IM chlorphenamine is used in anaphylaxis protocols after adrenaline — see local ALS/anaphylaxis guidance.
Antihistamines
Allergy, hay fever & urticaria — Irish brands
| Drug | Dose | Frequency | Type | Notes |
|---|---|---|---|---|
| Non-sedating (2nd generation) | ||||
| Cetirizine (Zirtek) | 10 mg | OD | Non-sedating | Hay fever, urticaria. Mild sedation possible in some; reduce in renal impairment. |
| Loratadine (Clarityn) | 10 mg | OD | Non-sedating | Hay fever, urticaria. Prefer if driving; less CNS effect than cetirizine. |
| Fexofenadine (Telfast) | 120–180 mg | OD | Non-sedating | 120 mg allergic rhinitis; 180 mg urticaria. Avoid antacids within 2 h. |
| Desloratadine (Neoclarityn) | 5 mg | OD | Non-sedating | Active metabolite of loratadine; prescription in Ireland. |
| Sedating (1st generation) | ||||
| Chlorphenamine (Piriton) | 4 mg | TDS–QDS (max 24 mg/day) | Sedating | Allergy, itch, insect bites. Sedation, anticholinergic effects; caution in elderly. |
| Promethazine (Phenergan) | 10–25 mg | OD–TDS (or nocte) | Sedating | Allergy, nausea, short-term sleep. Strongly sedating; avoid in elderly / delirium risk. |
Non-sedating (2nd generation)
Cetirizine (Zirtek)
Non-sedatingDose:10 mg
Frequency:OD
Notes: Hay fever, urticaria. Mild sedation possible in some; reduce in renal impairment.
Loratadine (Clarityn)
Non-sedatingDose:10 mg
Frequency:OD
Notes: Hay fever, urticaria. Prefer if driving; less CNS effect than cetirizine.
Fexofenadine (Telfast)
Non-sedatingDose:120–180 mg
Frequency:OD
Notes: 120 mg allergic rhinitis; 180 mg urticaria. Avoid antacids within 2 h.
Desloratadine (Neoclarityn)
Non-sedatingDose:5 mg
Frequency:OD
Notes: Active metabolite of loratadine; prescription in Ireland.
Sedating (1st generation)
Chlorphenamine (Piriton)
SedatingDose:4 mg
Frequency:TDS–QDS (max 24 mg/day)
Notes: Allergy, itch, insect bites. Sedation, anticholinergic effects; caution in elderly.
Promethazine (Phenergan)
SedatingDose:10–25 mg
Frequency:OD–TDS (or nocte)
Notes: Allergy, nausea, short-term sleep. Strongly sedating; avoid in elderly / delirium risk.
Educational reference only. Medical disclaimer