Drug resistance and in vitro susceptibility of Plasmodium falciparum in Thailand during 1988-2003

In vitro sensitivity of antimalarial drugs and correlation with clinico-parasitological response following treatment with a 3-day artesunate-mefloquine combination in patients with falciparum malaria along the Thai-Myanmar border

A 3-day artesunate-mefloquine combination therapy has been using as first-line treatment for acute uncomplicated Plasmodium falciparum malaria in Thailand since 1995 on the background of mefloquine resistance. The aim of the present study was to assess sensitivity of P. falciparum isolates (n=44) in an area along the Thai-Myanmar border (year 2009) to artesunate, mefloquine, chloroquine and quinine, including their correlation with clinico-parasitological response. Twenty, 19, and 5 isolates were collected from patients with 'Adequate Clinical and Parasitological Response (ACPR)', 'Late Parasitological Failure (LPF)' and 're-infection', respectively. The IC₅₀ of artesunate and mefloquine were significantly higher in patients with LPF compared with ACPR and re-infection. The proportion of isolates with declined artesunate or mefloquine sensitivity in the LPF group (47.4%) was significantly higher than the ACPR group (5.0%). A weak but statistical significant correlation (r=0.384, p=0.01) was observed between IC₅₀ values of artesunate and parasite clearance time (PCT). There was no significant relationship between in vitro sensitivity of parasite isolates to chloroquine or quinine and clinical response. In vitro susceptibility of P. falciparum isolates to artesunate and mefloquine may be used as a useful reliable tool to predict clinico-pathological response following a 3-day artesunate-mefloquine combination therapy.

Ex vivo drug sensitivity profiles of Plasmodium falciparum field isolates from Cambodia and Thailand, 2005 to 2010, determined by a histidine-rich protein-2 assay

Background

In vitro drug susceptibility assay of Plasmodium falciparum field isolates processed “immediate ex vivo” (IEV), without culture adaption, and tested using histidine-rich protein-2 (HRP-2) detection as an assay, is an expedient way to track drug resistance.

Methods

From 2005 to 2010, a HRP-2 in vitro assay assessed 451 P. falciparum field isolates obtained from subjects with malaria in western and northern Cambodia, and eastern Thailand, processed IEV, for 50% inhibitory concentrations (IC₅₀) against seven anti-malarial drugs, including artesunate (AS), dihydroartemisinin (DHA), and piperaquine.

Results

In western Cambodia, from 2006 to 2010, geometric mean (GM) IC₅₀ values for chloroquine, mefloquine, quinine, AS, DHA, and lumefantrine increased. In northern Cambodia, from 2009–2010, GM IC₅₀ values for most drugs approximated the highest western Cambodia GM IC₅₀ values in 2009 or 2010.

Conclusions

Western Cambodia is associated with sustained reductions in anti-malarial drug susceptibility, including the artemisinins, with possible emergence, or spread, to northern Cambodia. This potential public health crisis supports continued in vitro drug IC₅₀ monitoring of P. falciparum isolates at key locations in the region.

Pyronaridine-artesunate versus chloroquine in patients with acute Plasmodium vivax malaria: a randomized, double-blind, non-inferiority trial

Background

New antimalarials are needed for P. vivax and P. falciparum malaria. This study compared the efficacy and safety of pyronaridine-artesunate with that of chloroquine for the treatment of uncomplicated P. vivax malaria.

Methods and Findings

This phase III randomized, double-blind, non-inferiority trial included five centers across Cambodia, Thailand, India, and Indonesia. In a double-dummy design, patients (aged >3–≤60 years) with microscopically confirmed P. vivax mono-infection were randomized (1∶1) to receive pyronaridine-artesunate (target dose 7.2∶2.4 mg/kg to 13.8∶4.6 mg/kg) or chloroquine (standard dose) once daily for three days. Each treatment group included 228 randomized patients. Outcomes for the primary endpoint, Day-14 cure rate in the per-protocol population, were 99.5%, (217/218; 95%CI 97.5, 100) with pyronaridine-artesunate and 100% (209/209; 95%CI 98.3, 100) with chloroquine. Pyronaridine was non-inferior to chloroquine: treatment difference −0.5% (95%CI −2.6, 1.4), i.e., the lower limit of the 2-sided 95%CI for the treatment difference was greater than −10%. Pyronaridine-artesunate cure rates were non-inferior to chloroquine for Days 21, 28, 35 and 42. Parasite clearance time was shorter with pyronaridine-artesunate (median 23.0 h) versus chloroquine (32.0 h; p<0.0001), as was fever clearance time (median 15.9 h and 23.8 h, respectively; p = 0.0017). Kaplan-Meier estimates of post-baseline P. falciparum infection incidence until Day 42 were 2.5% with pyronaridine-artesunate, 6.1% with chloroquine (p = 0.048, log-rank test). Post-baseline P. vivax or P. falciparum infection incidence until Day 42 was 6.8% and 12.4%, respectively (p = 0.022, log rank test). There were no deaths. Adverse events occurred in 92/228 (40.4%) patients with pyronaridine-artesunate and 72/228 (31.6%) with chloroquine. Mild and transient increases in hepatic enzymes were observed for pyronaridine-artesunate.

Conclusion

Pyronaridine-artesunate efficacy in acute uncomplicated P. vivax malaria was at least that of chloroquine. As pyronaridine-artesunate is also efficacious against P. falciparum malaria, this combination has potential utility as a global antimalarial drug.

Trial registration

Clinicaltrials.gov NCT00440999