In 1936 Wolf1 reported startling effects of quinine in states of myotonia. He treated three siblings with myotonia congenita and one patient with myotonia atrophica with quinine and found that all myotonic manifestations disappeared. He reported that 10 grains (0.65 Gm.) of quinine dihydrochloride injected intravenously abolished every myotonic phenomenon within ten minutes after administration, the effect lasting from fifteen to twenty hours. He further found that quinine hydrochloride from 5 to 10 grains (0.32 to 0.65 Gm.) given by mouth two or three times a day proved to be an adequate maintenance dose for the eradication of the myotonia.
Wolf tried the remedies previously used in such states, such as thyroid substance, atropine, posterior pituitary, calcium chloride, salicylic acid and calcium gluconate, and found them without effect on his patients. Various stimulants and depressants of the autonomic nervous system and several alkaloids he found equally ineffective.
Lonergan RB, Paskind HA. QUININE IN MYOTONIA CONGENITA. JAMA. 1938;111(25):2292–2293. doi:10.1001/jama.1938.72790510003011b