Sensitivity of Plasmodium falciparum to Antimalarial Drugs in Hainan Island, China
AIM To observe the variation in resistance of Plasmodium falciparum after the cessation of chloroquine medication. METHODS WHO standard in vitro microtest and in vivo test were used. RESULTS In vitro test showed that the rate of chloroquine-resistant P. falciparum dropped from 97.9% in 1981 to 26.7% in 1997 (P < 0.001). The mean concentration of chloroquine for complete inhibition of schizont formation declined from 10.46 +/- 7.14 pmol/ul blood in 1981 to 1.63 +/- 1.47 pmol/microliter blood in 1997(P < 0.001). In vivo test showed that the rate of chloroquine-resistant P. falciparum decreased from 84.2% in 1981 to 18.4% in 1997(P < 0.001). The proportion of R III cases to the total resistant cases dropped from 53.1% in 1981 to 14.3% in 1997. CONCLUSION A tendency of progressive decline of resistance of the parasite was revealed after the cessation of chloroquine medication.