Promethazine is a first generation H1 antagonist used for sedation; nausea and vomiting (especially after anesthesia or chemotherapy); moderate to severe morning sickness; allergies (eg hay fever); common cold; motion sickness; pre-operative anxiety. It is available in four forms: oral tablet and oral solution, injectable solution and rectal suppository.
In Australia, promethazine is available S3 (Pharmacist only medicine)
Mechanism of Action:
Promethazine is derived from phenothiazine. It is a strong antagonist of the H1 receptor (antihistamine) and a moderate mACh receptor antagonist (anticholinergic).
Pharmacokinetics:
Bioavailability is 88% absorbed but after first-pass metabolism reduced to 25% absolute bioavailability; crosses blood/brain barrier; protein binding is 93%, mostly albumin; metabolised in the liver (glucuronidation and sulfoxidation); the elimination half-life is 10–19 hours; excretion is via kidney, breast milk and biliary.
Tradenames: Panquil®, Phenergan®, Phenadoz®, Promethegan® and many others
Chemical Formula: C17H20N2S
Dosage:
Allergy/rhinitis: Orally – 25mg at bedtime
Nausea and Vomiting: Orally or rectally – 12.5-25mg once every 4-6 hours as needed.
Motion Sickness: 25mg taken orally or rectally 30-60 minutes prior to departure.
Preoperative Sedation: 50mg taken orally or rectally on the night before the surgical procedure.
Postoperative Sedation: 25-50mg can be given intravenously, intramuscularly, orally or rectally.
Drug interactions:
The more severe interactions with promethazine include (but not limited to): astemizole; cisapride; disopyramide; ibutilide; indapamide; metrizamide; pentamidine; pimozide; procainamide; quinidine; sotalol; terfenadine
Contraindications:
Hypersensitivity; less than 2yrs of age; coma; jaundice; Reye’s syndrome
Use with caution in: asthma; peptic ulcer; hepatic impairment disease; respiratory impairment; bone marrow depression; those prone to anaphylaxis.
Pregnancy: Class C
Side Effects:
Commonest include: drowsiness; tardive dyskinesia; dry mouth; nausea; blurred vision; confusion; hyper- or hypotension; palpitations; neuroleptic malignant syndrome:
Promethazine can cause breathing problems in young children, so should not be used in those under two years.
In Australia, Promethazine is on the National Podiatry Scheduled Medicines List for use by authorised Podiatrists.
Examples of other H1 Antagonists (Anti-histamines):
| Highly Sedative: | Moderately Sedative: | Mildly Sedative: | Not Sedative: |
| Promethazine Hydroxyzine Dimenhydinate | Pheniramine Meclozine Cinnarizine | Triprolidine Clemastine Chlorpheniramine Dexchlorpheniramine | Desloratadine Fexofenadine Loratadine |
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