Oumaporn TasanorNoedl, HaraldKesara Na-BangchangKanungnit CongpuongJeeraphat SirichaisinthopWernsdorfer, Walther HMahidol University. Faculty of Tropical Medicine2015-11-132021-08-302015-11-132021-08-302015-11-132002https://repository.li.mahidol.ac.th/handle/20.500.14594/63378Joint International Tropical Medicine 2002: the 8th Chamlong-Tranakchit Harinsuta Lecture 20-22 November 2002 Montien Riverside Hotel, Bangkok, Thailand: abstract. Bangkok: Faculty of Tropical Medicine, Mahidol University; 2002. p. 184.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.engMahidol UniversityChloroquine sensitivityIn vitro testPlasmodi umiaxProceeding Poster