title: Changes in the resistance of Plasmodium falciparum to chloroquine in Hainan, China.
abstract: In 1979, in view of the widespread resistance of Plasmodium falciparum to chloroquine in the island of Hainan, China, it use as an antimalarial was suspended throughout the island. A longitudinal survey of the chloroquine-sensitivity of P. falciparum was carried out over the period 1981-91 to investigate whether its resistance had changed from the 1979 level. In-vitro assays were carried out every 2-3 years, while in-vivo tests were performed annually over the period 1981-83 and also in 1991. Resistance to chloroquine declined progressively after its use had stopped. The in-vitro tests indicated that the rate of chloroquine-resistant P. falciparum was 97.9% in 1981, but dropped to 60.9% in 1991 (P < 0.001). The mean concentration of chloroquine for complete inhibition of schizont formation was 10.4 pmol/microliters in 1981, but decreased to 3.0 pmol/microliters in 1991 (P < 0.001). The proportion of samples taken from malaria cases that required high concentrations ( > 6.4 pmol/microliters) of chloroquine for complete inhibition of schizont formation was 83.3% in 1981, but only 17.4% in 1991 (P < 0.001); at low concentrations ( > 1.6 pmol/microliters), the corresponding proportions increased from 4.2% in 1981 to 60.8% in 1991 (P < 0.001). In the 4-week in-vivo test, the rate of chloroquine-resistant P. falciparum decreased from 84.2% in 1981 to 40% in 1991 (P < 0.001). RII + RIII cases represented 59.4% of the total resistant cases in 1981, but decreased to 37.5% in 1991 (0.02 > P > 0.01).
authors.affiliation: Institute of Parasitic Diseases, Chinese Academy of Preventive Medicine, Shanghai.
authors.forename: D Q
authors.initials: DQ
authors.lastname: Liu
authors.forename: R J
authors.initials: RJ
authors.lastname: Liu
authors.forename: D X
authors.initials: DX
authors.lastname: Ren
authors.forename: D Q
authors.initials: DQ
authors.lastname: Gao
authors.forename: C Y
authors.initials: CY
authors.lastname: Zhang
authors.forename: C P
authors.initials: CP
authors.lastname: Qui
authors.forename: X Z
authors.initials: XZ
authors.lastname: Cai
authors.forename: C F
authors.initials: CF
authors.lastname: Ling
authors.forename: A H
authors.initials: AH
authors.lastname: Song
authors.forename: X
authors.initials: X
authors.lastname: Tang
mesh_terms: D000293:Adolescent; D000328:Adult; D000818:Animals; D000962:Antimalarials / Q000494:pharmacology*; D002648:Child; D002675:Child, Preschool; D002681:China; D002738:Chloroquine / Q000494:pharmacology*; D004351:Drug Resistance; D006801:Humans; D016778:Malaria, Falciparum / Q000188:drug therapy / Q000469:parasitology; D008875:Middle Aged; D010963:Plasmodium falciparum / Q000187:drug effects*
chemical_list: D000962:Antimalarials; D002738:Chloroquine