Question

The antihistamine diphenhydramine is a histamine receptor antagonist used to inhibit histamine release in allergic conditions. However, it also acts on the same receptors in the central nervous system, leading to somnolence (sleepiness or drowsiness). This adverse effect led to the design of second-generation antihistamines that do not cross the blood-brain barrier and thus do not induce drowsiness. The first of these new antagonists was the drug terfenadine. This drug inhibits histamine receptors in the G tract, large blood vessels, and bronchial muscle. However, terfenadine was found to also inhibit cardiac potassium channels, leading to potentially fatal arrhythmias. There was a sharp increase in the number of deaths due to cardiac arrhythmia in patients receiving terfenadine and this led to withdrawal of this drug from the market. In the case of these antihistamines, diphenhydramine leads to somnolence due totoxicity, and terfenadine leads to arrhythmias due totoxicity. o off-target; off-target X C off-target, on-target C on-target; off-target c on-target, on-target

Answer 1

On- Target means it acts on the thing which is expected. But off-target means it acts on other receptors other than expected.

So here, diphenhydramine leads to somnolence due to on- Target toxicity because the drug acts same excepted receptor but in a different area.

And terfinadine leads to arrythmias due to off- target toxicity.