In vitro interaction between artemisinin and chloroquine as well as desbutyl-benflumetol in Plasmodium vivax.

Malaria resulting from infection with Plasmodium vivax rarely causes death, however, patients usually suffer acute debilitating clinical symptoms and the recovery is slow. This study had the objective of assessing the pharmacodynamic interaction between artimisinin and chloroquine with a view of a potential acceleration of the clinicalparasitological response, and the investigation of therapeutic alternatives in the event of chloroquine resistance in Plasmodium vivax. Tests were based on the growth inhibition of Plasmodium vivax, determined by morphological differential counts of 200 asexual parasites. In total 45 isolates were evaluated successfully with parallel tests for artemisinin, chloroquine and desbutylbenflumetol (DBB) alone and combinations of artemisinin + chloroquine and artemisinin + DBB. Total inhibition was reached at a mean concentration of 1274.8 nM (95% CI 898.5 to 1808.7 nM), and 1852.2 nM (95% CI 1539.5 to 2228.6 nM) for artemisinin, and chloroquine respectively, whilst the 1:1 (m/m) combination of artemisinin and chloroquine was 1860.2 nM (95% CI 1454.4 to 2379.3 nM). EC(50) and EC(90) were 129.9 nM and 1058.5 nM for chloroquine, 32.6 nM and 735.5 nM for artemisinin, and 73.6 nM and 1103.0 nM for the 1:1 combination of both drugs. Interaction analysis according to Berenbaum yielded for the artemisinin + chloroquine combination at the EC(50) a mean SigmaFIC of 1.1126, at the EC(90) a mean SigmaFIC of 1.0331, and at the EC(99) a mean SigmaFIC of 1.1857. These results revealed marked additive interaction. For desbutylbenflumetol (DBB) the EC(50) and EC(90) were 1.5 nM and 28.8 nM, complete growth inhibition was observed at 90.4 nM (95% CI 75.1 to 108.7 nM). Interaction analysis indicated moderate antagonism at the lower concentration ranges, at the EC(90) additive interaction with a mean SigmaFIC of 1.0300, and synergism at the therapeutically most important EC(99) with a mean SigmaFIC of 0.5990.