Decreased In Vitro Susceptibility of Plasmodium falciparum Isolates to Artesunate, Mefloquine, Chloroquine, and Quinine in Cambodia from 2001 to 2007

Abstract

This study describes the results of in vitro antimalarial susceptibility assays and molecular polymorphisms of Plasmodium falciparum isolates from Cambodia. The samples were collected from patients enrolled in therapeutic efficacy studies (TES) conducted by the Cambodian National Malaria Control Program for the routine efficacy monitoring of artemisinin-based combination therapy (ACT) (artesunate-mefloquine and artemether-lumefantrine combinations). The isolates (n ‫؍‬ 2,041) were obtained from nine sentinel sites during the years 2001 to 2007. Among these, 1,588 were examined for their in vitro susceptibilities to four antimalarials (artesunate, mefloquine, chloroquine, and quinine), and 851 isolates were genotyped for single nucleotide polymorphisms (SNPs). The geometric means of the 50% inhibitory concentrations (GMIC 50 s) of the four drugs tested were significantly higher for isolates from western Cambodia than for those from eastern Cambodia. GMIC 50 s for isolates from participants who failed artesunate-mefloquine therapy were significantly higher than those for patients who were cured (P, <0.001). In vitro correlation of artesunate with the other drugs was observed. The distributions of the SNPs differed between eastern and western Cambodia, suggesting different genetic backgrounds of the parasite populations in these two parts of the country. The GMIC 50 s of the four drugs tested increased significantly in eastern Cambodia during 2006 to 2007. These results are worrisome, because they may signal deterioration of the efficacy of artesunate-mefloquine beyond the Cambodian-Thai border.

Factoring Quality Laboratory Diagnosis into the Malaria Control Agenda for Sub-Saharan Africa

“…Indiscriminate use of ACTs could create sufficient drug pressure that hastens development of resistant parasites, a situation that has begun to develop in Southeast Asia. [17][18][19] Furthermore, identifying febrile cases as having non-malarial causes provides opportunities to treat other potentially debilitating or fatal infections and also avoids unnecessary exposure to adverse events associated with ACTs. Therefore, laboratory-confirmed malaria is critical for appropriate management of malaria and other febrile diseases, maintaining the effectiveness of ACTs, and evaluating the effectiveness of interventions.…”

Ex Vivo Susceptibility of Plasmodium falciparum to Antimalarial Drugs in Western, Northern, and Eastern Cambodia, 2011-2012: Association with Molecular Markers

“…The use of PPQ monotherapy is believed to have selected PPQ-resistant parasites, which limited the use of PPQ by the late 1980s (15). The most recent data available for Cambodian P. falciparum isolates indicate that the geometric mean IC 50 s (GMIC 50 s) for CQ, MQ, quinine (QN), and ATS were significantly higher in western than eastern Cambodia from 2001 to 2011 (14,16), confirming a remarkable disparity in parasite drug sensitivity between these two regions. These GMIC 50 s were also significantly higher in patients with late treatment failures after ATS-MQ therapy than in those who had adequate clinical and parasitological responses (16).…”

“…The most recent data available for Cambodian P. falciparum isolates indicate that the geometric mean IC 50 s (GMIC 50 s) for CQ, MQ, quinine (QN), and ATS were significantly higher in western than eastern Cambodia from 2001 to 2011 (14,16), confirming a remarkable disparity in parasite drug sensitivity between these two regions. These GMIC 50 s were also significantly higher in patients with late treatment failures after ATS-MQ therapy than in those who had adequate clinical and parasitological responses (16). Importantly, the GMIC 50 s for all four drugs increased significantly from 2006 to 2007 in northeastern Cambodia (16), suggesting that multidrugresistant (MDR) parasites may be spreading to or emerging in areas other than Cambodia's western border with Thailand.…”

Methods for monitoring artemisinin-based combination therapies efficacy

“…The overall geometric means of IC 50 s (GMIC 50 s) of AS and MQ tested were significantly higher in the western than in the eastern provinces (P < 0.001) (Lim et al, 2010). This difference between western and eastern province could be explain by the higher resistance artemisinin rate in west compare to east of Cambodia.…”

“…Optical microtest was the first in vitro method widely used (Price et al, 2010;Tanariya et al, 2000). Standard in vitro and ex-vivo isotopic methods were developed initially for conventional antimalarial drugs but these methods were used to monitor ACTs partner drugs efficacy (Lim et al, 2010;Mwai et al, 2009;Pascual et al, 2012;Pradines et al, 1998Pradines et al, , 2011. Because of biosafety concerns with radioactive reagents, and the high cost of equipment and reagents, fluorometric and ELISA methods were developed to monitor ACTs partner drugs.…”