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H1-antihistamine (theoclate salt) Pregnancy: The use of Avomine is not recommended during pregnancy and in women of childbearing potential not using contraception, unless the potential benefits outweigh the potential risks. When promethazine has been given in high doses during late pregnancy, it has caused prolonged neurological disturbances in the infant. There are no available animal studies regarding reproductive toxicity. Breast-feeding: available evidence suggests that the amount excreted in milk is insignificant; however, there are risks of neonate irritability and excitement, and Avomine is not recommended for use in breast-feeding. Fertility: there are no relevant fertility data in animals.

Promethazine teoclate

Brand names: Avomine

Promethazine teoclate is a sedating, first-generation phenothiazine antihistamine used mainly to prevent and treat nausea and vomiting, including motion sickness.

Adult dose

Dose: Motion sickness, prevention on long journeys: one 25 mg tablet each evening at bedtime, starting the day before setting out (a second dose in 24 hours is not often necessary). Prevention on short journeys: one 25 mg tablet one or two hours before travelling or as soon after as possible. Treatment of motion sickness: one 25 mg tablet as soon as possible and repeated the same evening, followed by a third tablet the following evening. Nausea and vomiting due to other causes: one 25 mg tablet at night is often sufficient, but two or three tablets are sometimes necessary; alternatively 25 mg two or three times a day may be required for some patients
Route: Oral
Frequency: Motion sickness: prevention on long journeys once each evening at bedtime starting the day before; on short journeys once, 1 or 2 hours before travelling; treatment: as soon as possible, repeated the same evening, then a third tablet the following evening. Nausea and vomiting due to other causes: at night, or 25 mg two or three times a day
Source: UK SPC §4.1/§4.2 for Promethazine Teoclate 25 mg Tablets / Avomine 25 mg Tablets (each tablet contains promethazine teoclate 25 mg, §2). Indications (§4.1): prevention and treatment of nausea and vomiting, including motion sickness and post-operative vomiting; vertigo due to Meniere's syndrome, labyrinthitis and other causes — the §4.2 posology retrieved gives regimens only for motion sickness and for nausea and vomiting due to other causes, none for vertigo. The SPC does not print a maximum: 'It is often not necessary to give more than four of the 25 mg Avomine tablets in 24 hours' is guidance, so no maxDose is recorded. Elderly: no specific dosage recommendations. Should not be used for longer than seven days without seeking medical advice (§4.4). HYPEREMESIS GRAVIDARUM is NOT a labelled indication in this SPC, and §4.6 says use is not recommended during pregnancy unless the potential benefits outweigh the potential risks — no pregnancy-nausea regimen is written here. Tablets are not suitable for children aged 2 to 5 years (oral liquid recommended); not for children under 2 years. May interfere with immunologic urine pregnancy tests (false results) and should be discontinued at least 72 hours before skin tests using allergen extracts (§4.5).

Paediatric dose

Dose: In the above indications (motion sickness; nausea and vomiting): children over 10 years of age may be given the lower adult doses described in the SPC; children between 5 and 10 years may be given half the adult dose. Tablets are not suitable for children aged between 2 and 5 years (an oral liquid preparation is recommended). Not for use in children under 2 years of age
Route: Oral
Frequency: As for the adult regimen for the indication
THESE ARE THE LABEL'S OWN STATEMENTS (SPC §4.2 'Children'), not scaled doses by the drafter; the SPC expresses them relative to the adult doses, so no mg figure or dosePerKg is recorded. Contraindicated in children under two years because of the potential for fatal respiratory depression (§4.3). Avoid in children and adolescents with signs and symptoms suggestive of Reye's syndrome (§4.4). Paradoxical hyperexcitability and, in children under 6 years, psychomotor hyperactivity, aggression and hallucination have been reported (§4.8). Verify against a children's formulary.

Dose adjustments

Renal

No numeric renal dose adjustment is given. Avomine should be avoided in patients with renal dysfunction and used with care in renal insufficiency (§4.4).

Hepatic

No numeric hepatic dose adjustment is given. Avomine should be avoided in patients with liver dysfunction and used with care in hepatic insufficiency (§4.4).

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via MHRA Products — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • Known hypersensitivity to promethazine, other phenothiazines, or any excipient
  • Patients in coma or suffering from CNS depression of any cause
  • Children less than two years of age (potential for fatal respiratory depression)
  • Patients who have been taking monoamine oxidase inhibitors within the previous 14 days

Side effects

  • Sedation or somnolence (very common)
  • Dizziness, headache, tiredness, decreased appetite, blurred vision, nasal congestion (frequency not known)
  • Anticholinergic effects: paralytic ileus, urinary retention, dry mouth, constipation, accommodation disorder — the elderly are particularly susceptible to these and to confusion
  • Extrapyramidal effects including restless legs syndrome, muscle spasms and tic-like movements of the head and face, dystonia including oculogyric crisis (commoner in children and young adults, usually within the first 4 days of treatment or after dose increases), neuroleptic malignant syndrome, psychomotor hyperactivity
  • Agitation, confusional state, anxiety, hallucinations, aggression; in children paradoxical hyperexcitability, restlessness, nightmares, disorientation
  • Palpitations, arrhythmias, QT prolongation, Torsade de pointes; hypotension; respiratory depression
  • Allergic reactions including anaphylactic reaction, urticaria, angioedema; rash; photosensitivity reaction
  • Blood dyscrasias including haemolytic anaemia, agranulocytosis, leukopenia, eosinophilia, thrombocytopenia; cholestatic jaundice
  • The Yellow Card reporting paragraph at the end of §4.8 is cut off in the retrieved text

Interactions

  • Anticholinergic agents, tricyclic antidepressants, sedatives and hypnotics — their action is enhanced; alcohol should be avoided (enhances sedation)
  • Other products prolonging the QT interval (e.g. antipsychotics such as chlorpromazine, levomepromazine, sulpiride, amisulpride, tiapride, pimozide, haloperidol, droperidol, citalopram, halofantrine, methadone, pentamidine, moxifloxacin) — special caution required
  • Amitriptyline/amitriptylinoxide (CYP2D6 substrates) — plasma levels may rise; monitor for dose-dependent adverse reactions
  • Monoamine oxidase inhibitors — avoid within the previous 14 days and while using Avomine
  • Seizure-threshold-lowering drugs — concomitant use should be carefully considered
  • Non-absorbed gastro-intestinal agents (magnesium, aluminium and calcium salts, oxides and hydroxides) — may reduce absorption of phenothiazines; take at least 2 hours apart if possible
  • Immunologic urine pregnancy tests (false positive/negative) and allergen-extract skin tests (stop at least 72 hours before; false negatives)

Monitoring

  • Blood count if unexplained infection, fever or sore throat occurs (possible blood dyscrasia) — discontinue if marked changes (hyperleucocytosis, granulocytopenia) are observed
  • QT interval risk in patients with pronounced bradycardia, cardiovascular disease, hereditary QT prolongation or on other QT-prolonging products
  • Sedation and anticholinergic effects, particularly in the elderly
  • Signs of ototoxicity, intestinal obstruction or raised intracranial pressure, which promethazine may mask by suppressing vomiting
  • Treatment should not exceed seven days without seeking medical advice

Clinical monograph

How it works

It antagonises histamine H1 receptors and has central antimuscarinic and anti-emetic actions, dampening vestibular and chemoreceptor trigger zone input that drives nausea.

Prescribing in practice

  • It causes marked drowsiness and has antimuscarinic effects, so use cautiously in the elderly and avoid in those for whom sedation or anticholinergic burden is hazardous.
  • Avoid in patients with significant prostatic hypertrophy, urinary retention, narrow-angle glaucoma or pyloroduodenal obstruction owing to its antimuscarinic activity.
  • For motion sickness it is more effective taken before travel, and the teoclate salt is favoured for its longer duration of anti-emetic effect.

Monitoring

Routine monitoring is not generally needed, but assess for excessive sedation, anticholinergic effects and confusion, particularly in older patients.

Counselling the patient

  • Warn the patient that the medicine causes drowsiness and to avoid driving or operating machinery.
  • Advise avoiding alcohol while taking it.
  • For travel sickness, recommend taking it before the journey begins.

Evidence & guidelines

Promethazine teoclate is a well-established anti-emetic and antihistamine, with use for nausea and motion sickness supported by its SPC and long clinical experience.

Reference: RCOG GTG-69; 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).

Related

Curated clinical cross-links plus same-class fallbacks.

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