Hydroquinidine is a pharmaceutical agent that acts as a class I antiarrhythmic agent (Ia) in the heart. Hydroquinidine is a d-rotatory alkaloid derived from cinchiona bark. It is closely related to quinidine, differing from the latter alkaloid only in containing two more atoms of hydrogen in the molecule. The drug causes increased action potential duration, as well as a prolonged QT interval. It is not approved by FDA, but marketed in Spain, France, Italy and Pakistan under the brand names Lentoquine, Sérécor LP, Idrochinidina Lirca and Austacute, respectively. Like all other class I antiarrhythmic agents, Hydroquinidine primarily works by blocking the fast inward sodium current (INa). Hydroquinidine is also used for the treatment of Malaria.

Cinchonidine is an alkaloid found in Cinchona officinalis and Gongronema latifolium. Cinchonidine is an antimalarial drug which has been used clinically in malaria caused by Plasmodium falciparum. Cinchonidine is reported as an ingredient of Quinimax in a number of countries. Quinimax is a combination of four alkaloids (quinine, quinidine, cinchoine and cinchonidine).

QUININE PHOSPHATE, a salt of quinine, was formerly used for the treatment of malaria.

Quinine soluble salts possess the extremely bitter taste, that may have a perplexing problem especially to children. That is why the most common combinations which are administered in this way are the sulphate, salicylate, tannate and certain esters. Quinine tannate, an insoluble quinine salt has been known in medicine for a very long time. However, many experiments have revealed that quinine tannate was practically inert as a medicinal substance.