Sedating H1 antihistamine
Chlorphenamine maleate
Brand names: Piriton
Adult dose
Dose: PO 4mg every 4–6h (max 24mg/24h). IV/IM 10mg, may repeat up to QDS (max 40mg/24h)
Route: PO/IV/IM
Frequency: 4–6h
Paediatric dose
Route: PO
Frequency: 4–6h
Age bands
- 12–24m: 1mg BD
- 24–72m: 1mg every 4–6h, max 6mg/day
- 72–144m: 2mg every 4–6h, max 12mg/day
- 144–216m: 4mg every 4–6h, max 24mg/day
Clinical pearls
- First-line IV antihistamine in anaphylaxis adjunct (after adrenaline)
- Avoid in elderly — anticholinergic burden, falls
Contraindications
- Severe hepatic impairment
Side effects
- Sedation
- Anticholinergic effects
- Urinary retention
- Confusion in elderly
Interactions
- Additive sedation with CNS depressants
- Anticholinergic burden
Reference: BNFc; BNF; Resus Council UK anaphylaxis guidelines; https://bnf.nice.org.uk/drugs/chlorphenamine-maleate/. Verify against your local formulary and the latest BNF before prescribing.
Related
Curated clinical cross-links plus same-class fallbacks.
Calculators
Pathways
- New-Onset Atrial Fibrillation · ESC 2020 AF Guidelines; NICE NG196
- Hypertensive Emergency · ESC/ESH 2018 Hypertension Guidelines; NICE NG136
- Bradycardia Management · Resuscitation Council UK ABCDE; ESC 2021 Pacing Guidelines
- Ventricular Tachycardia / Fibrillation · Resuscitation Council UK ACLS; ESC 2022 Ventricular Arrhythmia Guidelines
- Syncope Assessment · ESC 2018 Syncope Guidelines; NICE NG109
- Acute Chest Pain · NICE CG95; ESC 2023 ACS Guidelines