Quinidine is a pharmaceutical agent that acts as a class I antiarrhythmic agent (Ia) in the heart. It is a stereoisomer of quinine, originally derived from the bark of the cinchona tree. The drug causes increased action potential duration, as well as a prolonged QT interval.

Norpethidine is a controlled drug because of its potential uses in manufacturing both pethidine itself and a range of N-substituted derivatives, but it has little opioid activity in its own right. Instead, norpethidine acts as a stimulant and causes convulsions.