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Drug Information
Pharmacokinetics
Promethazine is well absorbed
after oral or intramuscular administration. Peak plasma concentrations
have been observed 2 to 3 hours after administration by these routes,
although there is low systemic bioavailability after oral
administration, due to high first-pass metabolism in the liver.
Promethazine crosses the blood-brain barrier and the placenta, and is
distributed into breast milk. Values ranging from 76 to 93% have been
reported for plasma-protein binding. Promethazine undergoes extensive
metabolism, predominantly to promethazine sulphoxide, and also to N-desmethylpromethazine.
It is excreted slowly via the urine and bile, chiefly as metabolites.
Elimination half-lives of 5 to 14 hours have been reported.
Indication
& Dosage
Oral
ALLERGIC CONDITIONS: 25mg at night and 10mg during the day.
Parenteral
SEVERE ALLERGY: 25-50mg deep IM (max 100mg). Children (5-10yrs): IM
6.25-12.5mg) Slow IV inj (in emergencies): 25-50mg (upto 100mg).
Action
A phenothiazine which has very little dopaminergic action. It
is primarily an antithistamine with additional sedative and antiemetic
actions.
Alcohol:
CNS depression, extra-pyramidal reaction.
Aluminium Salts: Decrease efficacy. Antacids should be given 1 hour
before or 2 hours after promethazine.
Anticholinergics: Decrease efficacy and increase the anticholinergic
side-effects of promethazine.
Barbiturate anaesthetics: Increase frequency and severtiy of
neuromuscular excitation and hypotension.
Bromocriptine: Efficacy decreased by promethazine.
Lithium: Disorientation, unconsciousness and extra-pyramidal symptoms.
Meperidine: Excessive sedation and hypotension.
TCAs: Serum concentration increased by promethazine.
Propranolol: Increased plasma levels of both drugs.
MAOIs: Additive orhtostatic hypotensive effect.
Lab Test: Pregnancy tests: False positive results.
Plasma bound iodine(PBI): Increase in PBI occurs.
Adverse Effect & Precautions
Dry mouth, epigastric distress, restlessness, blurred vision, skin rash.
Precaution: Hypersensitivity.
Pregnancy: Contraindicated.
Breast Feeding: Contraindicated.
Man:May be given in reduced dose.
