Racemic mixture of two enantiomers with different pharmaeokinetic and pharmacodynamic propeies is seen in -

Ans. is 'c' i.e., Verapamil " Verapamil is prescribed as a racemate, L-Verapamil is a more potent calcium channel blocker than is dverapamil. However with oral therapy, the 1-enantiomer undergoes more extensive first - pass hepatic metabolism. For this reason, a given concentration of verapamil prolongs the PR interval to a greater extent when the drug is administered intravenously (where concentrations of the 1-and d-enantiomers are equivalent) than when it is administered orally."