Q. Reports of cardiac arrhythmias caused by unusually high blood levels of 2 antihistamines (terfenadine and astemizole) are best explained by (Solved)

1. Concomitant treatment with phenobarbital

2. Use of these drugs by smokers

3. Use of antihistamines by persons of Asian background

4. A genetic predisposition to metabolise succinylcholine slowly

5. Treatment of these patients with ketoconazole