Quinine is an antipyretic and antimalarial; also sometimes used in treating lupus and arthritis The following are the reasons for quinine appearing under “Skeletal Muscle Relaxants”
1. Quinine was used to relieve nocturnal leg cramps in recent past; now this use has been strongly warned against by the FDA
2. When directly injected into a nerve, it causes paralysis of muscle by direct action on the muscle
3. It has been show to ↑ refractory period and ↓ motor excitation at motor end-plate; the response of the muscle ↓ when exposed to repetitive neural stimulation
4. it has been shown to ↓ muscle tone in myotonia congenita and myotonic dystrophy
Reference: “Mechanism of action of Quinine in myotonia and myasthenia”; A.M Harvey; Journal of the American Medical Association 1939;112(16):1562-1563.