Abstract:  Objective   To assess the in vitro sensitivity of Plasmodium falciparum to chloroquine, piperaquine and pyronaridine in China-Myanmar border area.  Methods   Fifty-one blood specimens of P. falciparum isolates were collected from Laza City of Myanmar during September to December in 2009, and the sensitivity of the parasites to the drugs was detected by Rieckmann′s in vitro microtest.  Results   Among the 42 blood samples with valid results of sensitivity test,  the resistance rate to chloroquine, piperaquine and pyronaridine was 95.2%, 7.1%, and 54.8%, with a corresponding 50% inhibition dose(ID50 )of 320.5, 128.2, and 96.0 nmol/L, respectively. Pyronaridine-resistant P. falciparum exhibited some degree of cross-resistance to chloroquine [91.3%(21/23)] and piperaquine [13.0%(3/23)], and chloroquine-resistant P. falciparum showed cross-resistance to piperaquine [7.5%(3/40)] and pyronaridine [52.5%(21/40)]. High level of cross-resistance was present to chloroquine （100%） and pyronaridine （100%） in piperaquine-resistant P. falciparum.   Conclusion   In Laza City, P. falciparum shows high resistance to chloroquine, half isolates are resistant to pyronaridine, and most isolates are still sensitive to piperaquine.

Key words:  , Plasmodium falciparum；Sensitivity；In vitro microtest；Chloroquine；Piperaquine；Pyronaridine