First-generation H1-antihistamine (phenothiazine)
Promethazine hydrochloride
Brand names: Phenergan, Sominex
Adult dose
Dose: Allergy: 25mg PO ON, increase to 25mg BD-TDS. Insomnia: 20–50mg ON. Nausea: 25mg PO/IM/IV deep
Route: PO/IM/IV
Frequency: per indication
Clinical pearls
- Allergic reactions, motion sickness, sedation, hyperemesis gravidarum
- Avoid in elderly (anticholinergic burden)
Contraindications
- Children <2 (severe respiratory depression)
- Concurrent MAOI
Side effects
- Sedation
- Anticholinergic effects
- Paradoxical excitement (children)
- QT prolongation (high doses)
Interactions
- CNS depressants
- MAOIs
- Other antimuscarinics
Reference: BNF; MHRA; https://bnf.nice.org.uk/drugs/promethazine-hydrochloride/. 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