Caffeine interferes with drugs that regulate heart rhythm, such as quinidine and propranolol (Inderal).
Calisaya, known as the calisaya of Santa Fe, was strongly recommended for cultivation, because the shoots of felled trees afford bark containing a considerable amount of quinine; C. Pitayensia has been introduced into the Indian plantations on account of yielding the valuable alkaloid quinidine, as well as quinine.
Later quinidine and cinchonidine were discovered, and subsequently several other alkaloids, but in smaller quantity.
Quinine and quinidine In a small number of patients using quinine, or its stereoisomer quinidine, profound thrombocytopenia may occur.
Quinine, and its stereoisomer quinidine, are known to cause drug dependent antibody formation using the hapten mechanism.
The other alkaloids of cinchona bark - quinidine, cinchonidine, and cinchonine - also possess similar properties, but all are much less effective than quinine.
The sulphate of quinine used in medicine may contain up to 3% of cinchonidine, but should be free from cinchonine, quinidine and cupreine.
Traces of quinidine are also sometimes, though rarely, found in commercial quinine, but its presence does not detract in a medicinal point of view from the value of the latter.