[Fluctuation in the resistance of Plasmodium falciparum to chloroquine in China].
OBJECTIVE
To investigate whether chloroquine-resistance of Plasmodium falciparum had changed after stopping or reducing the use of chloroquine as an antimalarial in Hainan and Yunnan provinces.


METHODS
WHO standard in vitro microtest and 4-week in vivo test were used, assays were carried out in different time after stopping or reducing the use of chloroquine.


RESULTS
In vitro test in Hainan indicated that the rate of chloroquine-resistant P. falciparum was 97.9% in 1981, and dropped to 26.7% in 1997 (P<0.01). The mean concentration of chloroquine for complete inhibition of schizont formation was 10.46 +/- 7.14 pmol/microl blood in 1981, decreased to 1.63 +/- 1.47 pmol/microl blood in 1997 (P<0.01). The proportion of samples taken from malaria cases that required high concentration (>6.4 pmol/microl blood) of chloroquine for complete inhibition of schizont formation was 83.3% in 1981 and only 6.7% in 1997 (P<0.01). In the 4-week in vivo test, the rate of chloroquine-resistant P. falciparum decreased from 84.2% in 1981 to 18.4% in 1997 (P<0.01). RIII cases accounted for 53.1% of the total resistant cases in 1981, and for 14.3% in 1997 (P<0.01). In vitro test in Yunnan revealed that the rate of chloroquine-resistant P. falciparum, the mean concentration of chloroquine for complete inhibition of schizont formation and the proportion of samples taken from malaria cases that required >6.4 pmol/microl blood of chloroquine for complete inhibition of schizont formation were 97.4%, 17.2 +/- 12.6 pmol/microl blood and 58.9% in 1981 respectively, and dropped to 70.4% (P< 0.01), 4.0 +/- 3.3 pmol/microl blood (P<0.01) and 16.6% (P<0.01) in 2002 respectively.


CONCLUSIONS
The resistance of P. falciparum to chloroquine declined progressively after its use had been stopped or reduced in Hainan and Yunnan provinces.
Liu
De-quan
DQ
National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, WHO Collaborating Center for Malaria, Schistosomiasis and Filariasis, Shanghai 200025, China.
Feng
Xiao-ping
XP
Yang
Heng-lin
HL
Lin
Shi-gan
SG
Chen
Wen-jiang
WJ
Yang
Pin-fang
PF
D000293:Adolescent; D000328:Adult; D000818:Animals; D000962:Antimalarials / Q000494:pharmacology*; D002648:Child; D002675:Child, Preschool; 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*
D000962:Antimalarials; D002738:Chloroquine