Widened scope of drug repurposing/chiral switches, elements of secondary pharmaceuticals. The quinine/quinidine case

Drug repurposing to new medical uses and chiral switches are elements of secondary pharmaceuticals. This article focuses on drug repurposing/chiral switches of the diastereomeric quasi-enantiomeric antimalarial quinine and antiarrhythmic quinidine, based on the histories of these drugs (1638–2022), applying a widened scope. Quinine, an essential medicine, changed the world. Drug repurposing is a strategy for identifying new uses for approved or investigational drugs outside the scope of the original medical indications. Potential drugs are not included in the definition of drug repurposing. Drug repurposing may be within or outside the therapeutic group, e.g., quinidine to quinine repurposing, from treatment of arrhythmia or severe malaria to uncomplicated malaria. The scope of chiral switches included racemate to single enantiomer and other switches of the status of chirality, e.g., racemate and quasi-racemate to scalemic mixtures. There are 16 quinine/quinidine stereoisomers. Given the multiple pharmacological activities of Cinchona alkaloid stereoisomers, this article calls for subjecting them to comprehensive drug repurposing/chiral switch searches for new medical uses.