Antimalarial activity of the optical isomers of chloroquine diphosphate

Optically pure d- and l-Chloroquine Diphosphate were examined for their efficacy against Plasmodium berghei in mice. The d-enantiomer is significantly more effective than the corresponding l-enantiomer, and in subcurative doses the d-enantiomer is also signficantly more active than the racemate. This increased activity has however no influence upon Chloroquine-resistant strains of P. berghei. The LD50 in non-infected mice is higher for the d-enantiomer than for either the racemate or the l-enantiomer when mice were treated orally one and 4 times. These differences in efficacy and toxicity between the d- and l-enantiomer of Chloroquine are however not as pronounced as those found for the enantiomers of many other drugs and furthermore these differences are limited to subcurative doses.