A considerable number of alkaloids have been characterized in the bark, four of which account for 30% to 60% of the alklaoidal content. These are quinine, quinidine, cinchonidine and cinchonine. These are quinoline-containing structures representing two pairs of diastereoisomers. Quinine is usually the major component (one-half to two-thirds of total alkaloids), but the proportions of the four alkaloids vary according to species and hybrids. The alkaloids are often present in the bark in salt combination with quinic acid and cinchotannic acid.

Uses

Galenicals of cinchona have long been used as bitter tonics and stomachics. On account of the astringent effect due to tannins contained, a decoction and acid infusion are sometimes used as gargles. Huge quantities of cinchona bark are consumed in beverages such as vermouth and tonic water.

Quinine was the drug of choice for the treatment of malaria before World War II. However when its source was cut off by Japan during the war, a range of synthetic antimalarials was hastily produced as an alternative to quinine. Many such as chloroquine, primaquine and mefloquine are based on the structure of quinine. These drugs are much more active than quinine but associated with several adverse effects. Due to the ability of P. falciparum, the causative oraganism for malaria, to develop resistance to modern drugs, today cinchona alkaloids re-emerge as suitable for the treatment of chloroquine-resistant infections. Mixtures of cinchona alkaloids termed ‘totaquine’ were used as antimalarials during periods of quinine shortages.

Quinine exerts antimalarial action by intercalation of the quinoline moiety into the parasite’s DNA. It also complexes with the toxic breakdown products of haemoglobin formed by the parasite. Quinine finds use in the treatment of nocturnal cramps due to its skeletal muscle relaxant effect. Quinidine is administered in cardiac arrhythmias as it controls fibrillation and uncontrolled contraction of the muscle fibres of the heart.