No antidote for antihistamine overdose

The New Straits Times, July 17,1995

Q: I would like to find out whether ingesting three tablets of 2mg chlorpheniramine all at once could lead to poisoning. A few days ago, my 40-year-old brother accidentally took this amount. Since I was not sure of the possible danger, I quickly took him to the hospital for a medical check-up.

A: An antihistamine like chlorpheniramine is useful for treating various allergy-related itches, for relieving coughs and colds, motion sickness and as sleep aids. In general, 4mg to 8mg three to four times daily of chlorpheniramine constitute the usual adult daily dose. With this dosage, side-effects are rarely serious and often transient. The most common effect is sedation. Patients should be warned against driving or operating machinery.

Exceeding this daily dose by three to five times will put the patient at risk of developing toxicity. The patient may experience drowsiness, dilated pupils, flushed dry skin, fever, tachycardia, hallucinations, choreoathetoid movements and delirium. With larger doses, convulsions and hyperthermia may occur. The symptoms may begin to appear between 30 minutes and two hours after ingestion. Death, although rare, occurs usually within two to 18 hours.

Till today, there is no specific antidote for antihistamine overdose. Victim of antihistamine overdose should be brought to the hospital immediately for assessment and appropriate management if deemed necessary. In the case above the right action has been taken.