First-Generation Antihistamine — Burns Pruritus / Sedation Pregnancy: Use is not recommended during pregnancy or in women of childbearing potential not using contraception, unless the potential benefits outweigh the potential risks; advise effective contraception and to avoid becoming pregnant while receiving it. High doses given in late pregnancy have caused prolonged neurological disturbances in the infant. There are no available animal reproductive toxicity studies. Promethazine is excreted in breast milk with risks of neonatal irritability and excitement, and is not recommended in breast-feeding. Fertility: no relevant animal data.

Promethazine

Brand names: Phenergan

Promethazine is a sedating first-generation phenothiazine antihistamine with anticholinergic and antiemetic properties, used for allergic symptoms, sedation, and nausea including motion-related and procedural nausea.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: As an antihistamine in allergy (adults and children over 10 years, including the elderly): 25 mg as a single dose, increasing to a maximum of 25 mg twice a day as required

Route: Oral

Frequency: Single dose, best taken at night; may be increased to twice a day as required

Max: 25 mg twice a day for the allergy indication (adults and children over 10 years). For children 6-10 years the maximum daily dose is 25 mg. Phenergan should not be used for longer than 7 days without seeking medical advice.

Fetched UK SPC is Phenergan 25 mg tablets (https://www.medicines.org.uk/emc/product/5588/smpc). Other indications in §4.2 for adults and children over 10 years (including the elderly): AS AN ANTIEMETIC — 25 mg to be taken the night before the journey, to be repeated after 6-8 hours as required; AS A SEDATIVE for short-term use and for short-term treatment of insomnia — 25 mg or 50 mg as a single night-time dose. Single doses are best taken at night. Method of administration: oral. Caution — combined use with other sedative medicinal products is not recommended; phenothiazines may be additive with or potentiate other CNS depressants such as opiates or other analgesics, barbiturates or other sedatives, general anaesthetics or alcohol. Avoid in liver or renal dysfunction, Parkinson's disease, hypothyroidism, cardiac failure, phaeochromocytoma, myasthenia gravis or prostatic hypertrophy, and in patients with a history of narrow-angle glaucoma or agranulocytosis. Use caution in asthma, bronchitis or bronchiectasis (promethazine may thicken or dry lung secretions and impair expectoration), severe coronary artery disease, epilepsy, and bladder neck or pyloro-duodenal obstruction. Phenothiazine derivatives may potentiate QT prolongation with a risk of torsade de pointes, exacerbated by bradycardia, hypokalaemia and drug-induced QT prolongation. Promethazine may mask the warning signs of ototoxicity from ototoxic drugs (e.g. salicylates) and may delay early diagnosis of intestinal obstruction or raised intracranial pressure by suppressing vomiting. Avoid strong sunlight or ultraviolet light during or shortly after treatment (photosensitivity). PAEDIATRIC (no per-kg dose in this SPC): not for use in children under 6 years — contraindicated, due to the potential for fatal respiratory depression, psychiatric and CNS events. Children 6-10 years: allergy 25 mg as a single dose with a maximum daily dose of 25 mg; antiemetic — Phenergan Elixir is recommended for this age group; sedation/short-term insomnia 25 mg as a single night-time dose. Avoid in children and adolescents with signs and symptoms suggestive of Reye's Syndrome. Verify any under-18 dosing against a children's formulary. The US cross-check label fetched is promethazine hydrochloride RECTAL SUPPOSITORIES (a different route, with a boxed contraindication under 2 years) — its figures were not used here.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Known hypersensitivity to promethazine, other phenothiazines, or any other ingredient of the formulation
Patients in coma or suffering from CNS depression of any cause
Children less than 6 years of age
Patients taking monoamine oxidase inhibitors up to 14 days previously

Side effects

Sedation or somnolence (very common); dizziness, headache, tiredness (frequency not known)
Anticholinergic effects — paralytic ileus, urinary retention, dry mouth, constipation, accommodation disorder and blurred vision; the elderly are particularly susceptible, along with confusion
Extrapyramidal effects including restless legs, muscle spasms, tic-like movements of the head and face, and dystonia including oculogyric crisis (usually transitory, commoner in children and young adults, usually within the first 4 days or after dose increases)
Respiratory depression; nasal congestion
Palpitations and arrhythmias including QT prolongation and torsade de pointes; hypotension
Allergic reactions including anaphylactic reaction, urticaria and angioedema; rash and photosensitivity reaction; blood dyscrasias including haemolytic anaemia, agranulocytosis, leukopenia, eosinophilia and thrombocytopenia

Interactions

Monoamine oxidase inhibitors — avoid; contraindicated within 14 days of an MAOI, and an increased incidence of extrapyramidal effects has been reported with some MAOI/phenothiazine combinations
CNS depressants — alcohol, sedatives/hypnotics (including barbiturates), narcotics and narcotic analgesics, general anaesthetics, tricyclic antidepressants and tranquillisers: sedative action may be increased, prolonged or intensified; combined use with other sedatives is not recommended (eMC §4.4). US labelling advises reducing the barbiturate dose by at least one-half and the narcotic dose by one-quarter to one-half when given concomitantly
Adrenaline (epinephrine) — promethazine may reverse its vasopressor effect; adrenaline should NOT be used to treat hypotension associated with promethazine overdose (US label)
Other anticholinergic agents — use with caution (US label)
Other QT-prolonging drugs, and states causing bradycardia or hypokalaemia — additive risk of torsade de pointes (eMC §4.4). The eMC §4.5 was not captured in this fetch; verify against the UK SPC

Clinical monograph

How it works

It antagonises histamine H1 receptors and also blocks muscarinic and central receptors, producing sedation, antiemesis and relief of histamine-mediated symptoms such as pruritus.

Prescribing in practice

Its marked sedative effect is additive with opioids and other central depressants, so use cautiously where these are co-administered and monitor for excessive sedation and respiratory depression.
Anticholinergic effects can cause urinary retention, dry mouth, confusion and worsening of narrow-angle glaucoma, with the elderly particularly susceptible to confusion and falls.
Promethazine should be avoided in young children because of the risk of respiratory depression; in burns, itch from healing wounds is better managed with non-sedating measures where possible.

Monitoring

Monitor sedation level, anticholinergic effects and respiratory status, especially in older patients and those on concomitant opioids.

Counselling the patient

This can help with itching, sickness or sleep but is quite sedating.
Take care with drowsiness, particularly alongside strong painkillers.
Report difficulty passing urine, marked confusion or excessive sleepiness.

Evidence & guidelines

Promethazine's sedative and anticholinergic profile and its avoidance in young children are detailed in current prescribing references and MHRA advice on sedating antihistamines.

Reference: MHRA Promethazine Safety Update (Under-2s); BBA Burns Pruritus Management Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators