Clinical and In Vitro Resistance of Plasmodium falciparum to Artesunate-Amodiaquine in Cambodia

Clin Infect Dis. 2021 Aug 2;73(3):406-413. doi: 10.1093/cid/ciaa628.


Background: Artesunate-amodiaquine is a potential therapy for uncomplicated malaria in Cambodia.

Methods: Between September 2016 and January 2017, artesunate-amodiaquine efficacy and safety were evaluated in a prospective, open-label, single-arm observational study at health centers in Mondulkiri, Pursat, and Siem Reap Provinces, Cambodia. Adults and children with microscopically confirmed Plasmodium falciparum malaria received oral artesunate-amodiaquine once daily for 3 days plus single-dose primaquine, with follow-up on days 7, 14, 21, and 28. The primary outcome was day-28 polymerase chain reaction (PCR)-adjusted adequate clinical and parasitological response (ACPR). An amodiaquine parasite survival assay (AQSA) was developed and applied to whole genome sequencing results to evaluate potential amodiaquine resistance molecular markers.

Results: In 63 patients, day-28 PCR-adjusted ACPR was 81.0% (95% confidence interval [CI], 68.9-88.7). Day 3 parasite positivity rate was 44.4% (28/63; 95% CI, 31.9-57.5). All 63 isolates had the K13(C580Y) marker for artemisinin resistance; 79.4% (50/63) had Pfpm2 amplification. The AQSA resistance phenotype (≥45% parasite survival) was expressed in 36.5% (23/63) of isolates and was significantly associated with treatment failure (P = .0020). Pfmdr1 mutant haplotypes were N86/184F/D1246, and Pfcrt was CVIET or CVIDT at positions 72-76. Additional Pfcrt mutations were not associated with amodiaquine resistance, but the G353V mutant allele was associated with ACPR compared to Pfmdr1 haplotypes harboring F1068L or S784L/R945P mutations (P = .030 and P = .0004, respectively).

Conclusions: For uncomplicated falciparum malaria in Cambodia, artesunate-amodiaquine had inadequate efficacy owing to amodiaquine-resistant P. falciparum. Amodiaquine resistance was not associated with previously identified molecular markers.

Keywords: Plasmodium falciparum; Cambodia; artemisinin; artesunate-amodiaquine; drug resistance.

Publication types

  • Research Support, Non-U.S. Gov't
  • Comment

MeSH terms

  • Adult
  • Amodiaquine / pharmacology
  • Amodiaquine / therapeutic use
  • Antimalarials* / pharmacology
  • Antimalarials* / therapeutic use
  • Artemisinins* / pharmacology
  • Artemisinins* / therapeutic use
  • Artesunate / therapeutic use
  • Asia
  • Cambodia
  • Child
  • Humans
  • Malaria* / drug therapy
  • Malaria, Falciparum* / drug therapy
  • Plasmodium falciparum / genetics
  • Prospective Studies


  • Antimalarials
  • Artemisinins
  • Amodiaquine
  • Artesunate