“May all be happy, may all be healed, may all be at peace and may no one ever suffer."
Promethazine is a phenothiazine derivative which blocks postsynaptic mesolimbic dopaminergic receptors in the brain. It exhibits strong α-adrenergic blocking effect and depresses the release of hypothalamic and hypophyseal hormones. It competes with histamine for the H1-receptor; muscarinic blocking effect may be responsible for antiemetic activity. It also reduces stimuli to the brainstem reticular system.
Promethazine is well absorbed from the gastrointestinal tract. Clinical effects are apparent within 20 minutes after oral administration and generally last four to six hours, although they may persist as long as 12 hours. Promethazine is metabolized by the liver to a variety of compounds; the sulfoxides of promethazine and N-demethylpromethazine are the predominant metabolites appearing in the urine.
Adults: Initial dose one 25 mg tablet at night; may be increased to two or three 25 mg tablets at night if necessary. In allergic conditions more frequently administration, twice or three times daily, may be necessary, starting with one or two 10 mg tablets and increasing as required.
Elderly: No specific dosage recommendations.
Children: They may be treated more conveniently by the elixir containing 5 mg/5 ml.
As an antihistamine in allergy:
As a sedative:
Use this drug only as recommended. Do not exceed the recommended dose. There have been case reports of promethazine abuse. Do not take for longer than 10 days.
Overdose Effects
Symptoms of severe over dosage are variable. They are characterised in children by various combinations of excitation, ataxia, incoordination, athetosis and hallucinations, while adults may become drowsy and lapse into coma. Convulsions may occur in both adults and children; coma or excitement may precede their occurrence. Tachycardia may develop. Cardiorespiratory depression is uncommon. If the patient is seen soon enough after ingestion, it should be possible to induce vomiting with ipecacuanha despite the antiemetic efect of promethazine; alternatively, gastric lavage may be used. Treatment is otherwise supportive with attention to maintenance of adequate respiratory and circulatory status. Convulsions should be treated with diazepam or other suitable anticonvulsant.
Pregnancy & Lactation
There is epidemiological evidence for the safety of promethazine in pregnancy and animal studies have shown no hazard, nevertheless, it should not be used in pregnancy unless the physician considers it essential. The use of Phenergan is not recommended in the two weeks prior to delivery in view of the risk of irritability and excitement in the neonate. When promethazine has been given in high doses during late pregnancy, promethazine has caused prolonged neurological disturbances in the infant. Promethazine should be used in pregnancy only if the potential benefts to the patient are weighed against the possible risk to the fetus. Promethazine is excreted in breastmilk. There are risks of neonatal irritability and excitement.