title: In-vitro response of Plasmodium falciparum to the main alkaloids of Cinchona in northwestern Thailand.
abstract: The blood schizontocidal activity of the four main Cinchona alkaloids against Plasmodium falciparum was compared in 46 fresh parasite isolates, using an in-vitro test measuring the drug-specific inhibition of schizont maturation. The studies were conducted in June-August 2001 at Mae Sot, northwestern Thailand, an area where quinine alone is no longer able to eliminate infections with P. falciparum. Quinidine showed the highest blood schizontocidal activity, followed by cinchonine, cinchonidine and finally quinine, which was identified as the least active compound. The isolates showed marked heterogeneity in their response to the Cinchona alkaloids. There was also high correlation of activity among all four alkaloids. The mean EC50 values for quinine, quinidine, cinchonine and cinchonidine were 144 nM, 80 nM, 104 nM and 225 nM, respectively, and the EC99 values 8040 nM, 861 nM, 1176 nM and 6531 nM. The EC99 values for quinine and cinchonidine are beyond the therapeutic concentration range and those for quinidine within it. For cinchonine, values are likely to be within this range, but toxicological and pharmacokinetic studies on this compound are required for clarifying its potential future role in the treatment of falciparum malaria.
authors.affiliation: Department of Medical Parasitology, Institute of Hygiene, University of Graz, Graz, Austria.
authors.forename: Ariane
authors.initials: A
authors.lastname: Knauer
authors.forename: Jeeraphat
authors.initials: J
authors.lastname: Sirichaisinthop
authors.forename: Franz F
authors.initials: FF
authors.lastname: Reinthaler
authors.forename: Gerhard
authors.initials: G
authors.lastname: Wiedermann
authors.forename: Gunther
authors.initials: G
authors.lastname: Wernsdorfer
authors.forename: Walther H
authors.initials: WH
authors.lastname: Wernsdorfer
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D000962:Antimalarials / Q000008:administration & dosage; D049109:Cell Proliferation / Q000187:drug effects; D002738:Chloroquine / Q000008:administration & dosage*; D002930:Cinchona Alkaloids / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D004338:Drug Combinations; D004341:Drug Evaluation / Q000379:methods; D006801:Humans; D016778:Malaria, Falciparum / Q000097:blood* / Q000188:drug therapy / Q000469:parasitology*; D008517:Phytotherapy / Q000379:methods; D010936:Plant Extracts / Q000008:administration & dosage*; D010963:Plasmodium falciparum / Q000145:classification / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development; D013045:Species Specificity; D013785:Thailand
chemical_list: D000962:Antimalarials; D002930:Cinchona Alkaloids; D004338:Drug Combinations; D010936:Plant Extracts; D002738:Chloroquine