title: An in vitro system for assessing the sensitivity of Plasmodium vivax to chloroquine.
abstract: Following earlier observations on short-term culture of Plasmodium vivax, an in vitro test system has been developed for assessing the parasite's sensitivity to chloroquine. Fresh isolates with predominantly young trophozoites are diluted 1:19 with a (v/v=1/1) mixture of RPMI 1640 and Waymouth medium. The blood-medium mixture (BMM) is inoculated into the predosed microtitre plates before incubation in a candle jar. Incubation for 30 or 42 h yielded the best results. Incubation for 18 or 24 h was generally insufficient for an adequate development of the parasites. The reading of the test is based on stage-specific differential counts in the Giemsa-stained pre-incubation and post-incubation thick films, the evaluation on log-probit analysis of drug-related inhibition of parasite development. The test system has been evaluated on 200 fresh P. vivax isolates in an area with satisfactory clinical-parasitological response to chloroquine. At 30 or 42 h incubation 121 isolates (61.5%) showed adequate control growth and yielded valid sensitivity tests. Complete inhibition of parasite development occurred within the concentration range of 40-1280 nM. The mean EC50 for 30 h of incubation was 50.3 nM, as compared to 49.7 nM with 42 h of incubation. The geometric mean cut-off concentration of parasite development was 488 nM with 30 h of incubation as against 470 nM with 42 h of incubation.
authors.affiliation: Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
authors.forename: Oumaporn
authors.initials: O
authors.lastname: Tasanor
authors.forename: Harald
authors.initials: H
authors.lastname: Noedl
authors.forename: Kesara
authors.initials: K
authors.lastname: Na-Bangchang
authors.forename: Kanungnit
authors.initials: K
authors.lastname: Congpuong
authors.forename: Jeeraphat
authors.initials: J
authors.lastname: Sirichaisinthop
authors.forename: Walther H
authors.initials: WH
authors.lastname: Wernsdorfer
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000494:pharmacology*; D002478:Cells, Cultured; D002738:Chloroquine / Q000494:pharmacology*; D021261:Parasitic Sensitivity Tests; D010966:Plasmodium vivax / Q000187:drug effects*; D013785:Thailand
chemical_list: D000962:Antimalarials; D002738:Chloroquine