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

Abstract

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.

Desbutyl-Lumefantrine Is a Metabolite of Lumefantrine with Potent In Vitro Antimalarial Activity That May Influence Artemether-Lumefantrine Treatment Outcome

“…The lack of an in vitro interaction between DBL and lumefantrine appears to contradict previous reports of synergy in field isolates of P. falciparum using limited numbers of drug combinations (23,24). However, the synergy between DBL and dihydroartemisinin that we observed using dual methods of isobolographic data analysis parallels data from studies of field isolates of P. vivax (13) and P. falciparum (16). We were able to detect both lumefantrine and DBL at mean concentrations that were well above the IC 99 for both laboratory-adapted strains of P. falciparum in day 7 plasma of children treated with artemether-lumefantrine for uncomplicated malaria.…”

“…The relatively short half-lives of artemether and its active metabolite dihydroartemisinin (1 to 2 h) (8, 9) limit the time window for such effects. Interactions can be antagonistic, such as those between artemisinin and DBL at some concentrations (13) and between dihydroartemisinin and 4-aminoquininolines and related drugs (6). The fact that a range of different ACTs show equal efficacy (22) suggests that acute effects on the parasite other than those from the artemisinin drug are minor.…”

“…DBL is more potent in vitro against chloroquine (CQ)-resistant Plasmodium falciparum and Plasmodium vivax field isolates than lumefantrine (13,17,23). There is evidence of in vitro synergy between lumefantrine and DBL against P. falciparum but at ratios (999:1 and 995:5) that were presumably selected at a time when plasma concentrations of DBL were assumed to be very much lower than those of the parent compound (23,24).…”

“…There is evidence of in vitro synergy between lumefantrine and DBL against P. falciparum but at ratios (999:1 and 995:5) that were presumably selected at a time when plasma concentrations of DBL were assumed to be very much lower than those of the parent compound (23,24). Interactions between DBL and artemisinin were assessed in a study of schizont maturation in Thai P. vivax field isolates in which antagonism was found at low concentrations and apparent synergy was found at much higher concentrations (13). A subsequent similar field study confirmed the concentration-dependent synergy in strains of P. falciparum (16).…”

Synergism between monodesbutyl-benflumetol and artemisinin in Plasmodium falciparum in vitro

“…5 represented the FICs of two highly artemisinin-and DBB-sensitive isolates. In the light of these observations the relatively moderate interaction between artemisinin and DBB in P. vivax [12] may be explained by a still highly sensitive response of this species to both, artemisinin and DBB.…”