Changes in the resistance of Plasmodium falciparum to chloroquine in Hainan, China

• Published in: Bulletin of the World Health Organization 1995-07, Vol.73 (4), p.483-486
• Main Authors: Liu, D Q, Liu, R J, Ren, D X, Gao, D Q, Zhang, C Y, Qui, C P, Cai, X Z, Ling, C F, Song, A H, Tang, X
• Format: Article
• Language: English
• Subjects: Adolescent; Adult; Animals; Antibiotics. Antiinfectious agents. Antiparasitic agents; Antimalarials - pharmacology; Antiparasitic agents; Biological and medical sciences; Child; Child, Preschool; China; Chloroquine; Chloroquine - pharmacology; Drug Resistance; Humans; Malaria, Falciparum - drug therapy; Malaria, Falciparum - parasitology; Medical sciences; Middle Aged; Pharmacology. Drug treatments; Physiological aspects; Plasmodium falciparum; Plasmodium falciparum - drug effects
• ISSN: 0042-9686; 1564-0604

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).