Pharath LimDalin DekVorleak TryRichard T. EastmanSophy ChySokunthea SrengSeila SuonSivanna MaoChantha SophaBaramey SamElizabeth A. AshleyOlivo MiottoArjen M. DondorpNicholas J. WhiteXin Zhuan SuMeng Chuor CharJennifer M. AndersonChanaki AmaratungaDidier MenardRick M. FairhurstNational Institute of Allergy and Infectious DiseasesNational Center for Parasitology, Entomology and Malaria ControlInstitut Pasteur du CambodgeSampov Meas Referral HospitalMakara 16 Referral HospitalRatanakiri Referral HospitalMahidol UniversityUniversity of Oxford2018-10-192018-10-192013-11-01Antimicrobial Agents and Chemotherapy. Vol.57, No.11 (2013), 5277-528310986596006648042-s2.0-84885941960https://repository.li.mahidol.ac.th/handle/20.500.14594/32098In 2008, dihydroartemisinin (DHA)-piperaquine (PPQ) became the first-line treatment for uncomplicated Plasmodium falciparum malaria in western Cambodia. Recent reports of increased treatment failure rates after DHA-PPQ therapy in this region suggest that parasite resistance to DHA, PPQ, or both is now adversely affecting treatment. While artemisinin (ART) resistance is established in western Cambodia, there is no evidence of PPQ resistance. To monitor for resistance to PPQ and other antimalarials, we measured drug susceptibilities for parasites collected in 2011 and 2012 from Pursat, Preah Vihear, and Ratanakiri, in western, northern, and eastern Cambodia, respectively. Using a SYBR green I fluorescence assay, we calculated the ex vivo 50% inhibitory concentrations (IC50s) of 310 parasites to six antimalarials: chloroquine (CQ), mefloquine (MQ), quinine (QN), PPQ, artesunate (ATS), and DHA. Geometric mean IC50s (GMIC50s) for all drugs (except PPQ) were significantly higher in Pursat and Preah Vihear than in Ratanakiri (P ≤ 0.001). An increased copy number of P. falciparum mdr1 (pfmdr1), an MQ resistance marker, was more prevalent in Pursat and Preah Vihear than in Ratanakiri and was associated with higher GMIC50s for MQ, QN, ATS, and DHA. An increased copy number of a chromosome 5 region (X5r), a candidate PPQ resistance marker, was detected in Pursat but was not associated with reduced susceptibility to PPQ. The ex vivo IC50and pfmdr1 copy number are important tools in the surveillance of multidrug-resistant (MDR) parasites in Cambodia. While MDR P. falciparum is prevalent in western and northern Cambodia, there is no evidence for PPQ resistance, suggesting that DHA-PPQ treatment failures result mainly from ART resistance. Copyright © 2013, American Society for Microbiology.Mahidol UniversityMedicinePharmacology, Toxicology and PharmaceuticsArticleSCOPUS10.1128/AAC.00687-13