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Promethazine is a phenothiazine derivative with potent antihistaminic and sedative-hypnotic effects. It also has antiemetic, antivertigo, anti-motion sickness, anticholinergic effects and local anaesthetic actions.
Antihistamines competitively and reversibly antagonize the effects of histamine at the H1-receptor sites on effector cells which are responsible for vasodilation, increased capillary permeability, flare and itch reactions in the skin and to some extent for contraction of smooth muscle in the bronchi and gastrointestinal tract.
Indications
Promethazine Hydrochloride injection is indicated for the following conditions:
- Treatment of allergic reactions such as: uncomplicated allergic conditions of the immediate type, e.g. pruritus, urticarial and angioedema, when oral therapy is impossible or contraindicated
- Treatment and prevention of vomiting including: motion sickness; drug induced nausea; prevention and control of nausea and vomiting associated with certain types of anaesthesia and surgery, such as procedures with a high incidence of postoperative vomiting (e.g. gynecological surgery, strabismus or middle ear surgery, and electroconvulsive therapy); in patients with a past history of motion sickness or post-operative vomiting; and in patients with whom avoidance of vomiting is crucial (e.g. Neurosurgery and eye surgery);
- Promethazine has sedative effects and it is also used in: preoperative, postoperative and obstetric (during labour) sedation.
Contraindications
- Promethazine is contraindicated for use in pediatric patients less than two years of age.
- Promethazine is contraindicated in patients who have exhibited hypersensitivity to the drug or other phenothiazine derivatives.
- Promethazine is also contraindicated in the following patients: comatose after administration of large doses of other CNS depressants (e.g. alcohol general anaesthetics, opioid analgesics, traquillisers, etc.)
- Promethazine injection must not be administered intra-arterially due to the likelihood of severe arteriospasm and the possibility of resultant gangrene
- Promethazine injection should not be given subcutaneously, as the solution is irritant and may produce necrotic lesions.
Precautions
Promethazine should not be used in pediatric patients less than two years of age because of the potential for fatal respiratory depression.
Use of promethazine should be avoided in acutely ill or dehydrated children. Use of the drug should also be avoided in children and adolescents with signs and symptoms which suggest Reye’s.
Promethazine may impair the mental and/or physical abilities required for the performance of potentially hazardous tasks such as driving a vehicle or operating machinery. The concomitant administration of alcohol, sedative-hypnotics, general anaesthetics, opioids, tranquillizers or other CNS depressants may have an additive sedative effect. Patients should be warned accordingly.
Promethazine injection contains sodium metabisulfite, which may cause allergic type-reactions, including anaphylactic symptoms and life-threatening or less severe asthmatic episodes, in certain susceptible people.
Use in pregnancy
When given in high doses during late pregnancy, phenothiazine have cause prolonged extrapyramidal disturbances in the child.
Use in lactation
The exact amount of promethazine excreted into breast milk is unknown, but amounts are usually small. Promethazine should be used with caution in nursing women. The infant should be observed for side effects, especially sedation.
Interactions with other drugs
Promethazine has history of interactions with Anticholinergics, anticonvulsants, antihypertensive agents, bromocriptine, CNS depressants, Levodopa, metrizamide, monoamine oxidase (MAO) inhibitors, Phenothiazine derivatives, Quinidine, sympathomimetic agents and tricyclic antidepressants.
Drug incompatibilities
Solutions of promethazine hydrochloride are incompatible with alkaline substances, which precipitate the insoluble promethazine base.
Adverse reactions
CNS: sedation is the most prominent CNS effect of promethazine. Extrapyramidal reactions may occur with high doses and usually subside with dosage reduction. Other reported reactions include dizziness, lassitude, tinnitus, confusion, disorientation, convulsions, incoordination, fatigue, blurred vision, euphoria, diplopia, nervousness, irritability, tremors, convulsions, oculogyric crises, excitation, catatonic-like states, and hysteria.
Cardiovascular: tachycardia, bradycardia, faintness, dizziness, transient minor increases in blood pressure and hypotension have been reported.
Gastrointestinal: nausea, vomiting, loss of appetite, epigastric distress, constipation.
Dosage and administration
The preferred route of administration of Promethazine hydrochloride injection is by deep intramuscular injection. Intramuscular injection may be painful.
Intravenous administration of this product is generally well tolerated, however extreme care must be taken to avoid extravasation or intra-arterial injection. When given intravenously promethazine injection 25mg/1ml should be diluted in 1 to 10 with water for injection or preferably given through the tubing of a freely flowing I.V infusion. It should be injected slowly at a rate of administration not greater than 25mg/minute (i.e. 10ml/minute) of dilute solution. Rapid intravenous infusion may cause a transient fall in blood pressure. Promethazine should not be given intra-arterially or subcutaneously.
Allergic conditions
Adults: 25-50mg by deep intramuscular injection or slow intravenous injection; may be repeated within two hours if necessary. Maximum dose up to 150mg daily.
Antiemetic
Antiemetic should not be used in vomiting of unknown etiology in children and adolescents
In established nausea or vomiting due to cause other than motion sickness:
Adult: 12.5-25mg, by intramuscular or intravenous injection, every four hours as needed
Children: 5-12 years old; 12.5mg by intramuscular injection
Sedative /hypnotic
Adults: 25-50mg by intramuscular or intravenous injection.
Children: when oral route is not possible:
2-5 years old; 7.5-10mg by intramuscular injection
6-10 years old; 12.5mg by intramuscular injection
Preoperative and postoperative sedation
Adults: 25-50mg by intramuscular or intravenous injection, usually with pethidine and atropine one hour before surgery
Obstetric sedation
Early stage of labour: 50mg, by intramuscular injection.
Established labour: 25-75mg, by intramuscular or intravenous injection, with an appropriately reduced dose of an opioid analgesic. May be repeated once or twice at four hourly intervals during the course of the labour, if necessary. Total dose should not exceed 100mg in 24 hours.
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