title: Drug resistance and in vitro susceptibility of Plasmodium falciparum in Thailand during 1988-2003.
abstract: The aim of the present study was to investigate antimalarial drug pressure resulting from the clinical use of different antimalarials in Thailand. The phenotypic diversity of the susceptibility profiles of antimalarials, i.e., chloroquine (CQ), quinine (QN), mefloquine (MQ), and artesunate (ARS) in Plasmodium falciparum isolates collected during the period from 1988 to 2003 were studied. P. falciparum isolates from infected patients were collected from the Thai-Cambodian border area at different time periods (1988-1989, 1991-1992, and 2003), during which 3 different patterns of drug use had been implemented: MQ + sulphadoxine (S) + pyrimethamine (P), MQ alone and MQ + ARS, respectively. The in vitro drug susceptibilities were investigated using a method based on the incorporation of [(3)H] hypoxanthine. A total of 50 isolates were tested for susceptibilities to CQ, QN, MQ, and ARS. Of these isolates, 19, 16, and 15 were adapted during the periods 1988-1989, 1991-1993, and 2003, respectively. P. falciparum isolates collected during the 3 periods were resistant to CQ. Sensitivities to MQ declined from 1988 to 2003. In contrast, the parasite was sensitive to QN, and similar sensitivity profile patterns were observed during the 3 time periods. There was a significantly positive but weak correlation between the IC(50) values of CQ and QN, as well as between the IC(50) values of QN and MQ. Drug pressure has impact on sensitivity of P. falciparum to MQ. A combination therapy of MQ and ARS is being applied to reduce the parasite resistance, and also increasing the efficacy of the drug.
authors.affiliation: Pharmacology and Toxicology Unit, Graduate Program in Biomedical Sciences, Faculty of Allied Health Sciences, Thammasat University, Rangsit, Patumthani, Thailand.
authors.forename: Nantana
authors.initials: N
authors.lastname: Suwandittakul
authors.forename: Wanna
authors.initials: W
authors.lastname: Chaijaroenkul
authors.forename: Pongchai
authors.initials: P
authors.lastname: Harnyuttanakorn
authors.forename: Mathirut
authors.initials: M
authors.lastname: Mungthin
authors.forename: Kesara
authors.initials: K
authors.lastname: Na Bangchang
mesh_terms: D000818:Animals; D000962:Antimalarials / Q000494:pharmacology* / Q000627:therapeutic use; D037621:Artemisinins / Q000494:pharmacology / Q000627:therapeutic use; D000077332:Artesunate; D002738:Chloroquine / Q000494:pharmacology / Q000627:therapeutic use; D004351:Drug Resistance; D006801:Humans; D008288:Malaria / Q000188:drug therapy / Q000469:parasitology*; D015767:Mefloquine / Q000494:pharmacology / Q000627:therapeutic use; D021261:Parasitic Sensitivity Tests / Q000379:methods; D010963:Plasmodium falciparum / Q000187:drug effects* / Q000302:isolation & purification; D011803:Quinine / Q000494:pharmacology / Q000627:therapeutic use; D013785:Thailand
chemical_list: D000962:Antimalarials; D037621:Artemisinins; D000077332:Artesunate; D002738:Chloroquine; D011803:Quinine; D015767:Mefloquine