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Background  Reduced artemisinin susceptibility and artemisinin-based combination therapy (ACT)-resistance against  Plasmodium falciparum  and chloroquine (CQ)-resistant  P. vivax  malaria has been reported in Vietnam. Two therapeutic efficacy studies were conducted in Thuan Bac District (Ninh Thuan Province, Vietnam) in 2015 and 2016 to determine the extent of reduced artemisinin susceptibility and ACT resistant falciparum malaria, and CQ-resistant vivax malaria were present.    Methods  Twenty-seven patients with falciparum malaria were randomized to receive artesunate alone (AS ~ 4 mg/kg/day) for 4 days followed by dihydroartemisinin (DHA) (2.2 mg/kg)–piperaquine (PPQ) (18 mg/kg) daily for 3 days or artemether (AM) (1.7 mg/kg)–lumefantrine (LUM) (12 mg/kg) twice daily for 3 days. Sixteen subjects with vivax malaria received CQ (total 25 mg/kg over 3 days). The therapeutic efficacy study for treating falciparum malaria was complemented with molecular analysis for artemisinin and piperaquine resistance, and in vitro drug susceptibility testing. Patient’s drug exposure following both falciparum and vivax treatment studies was determined.    Results  Twenty-five of 27 patients treated with the artemisinin regimens completed the 42-day follow-up period. None had parasites present on day 3 after commencing treatment with no incidence of recrudescence (100% curative rate). One patient on AS + DHA–PPQ was lost to follow-up and one patient had  Plasmodium falciparum  and  Plasmodium vivax  infection on day 0 by PCR. Of the vivax patients, 15 of 16 completed CQ treatment and two had a recurrence of vivax malaria on day 28, a failure rate of 13.3% (2/15). No mutations in the  Pfkelch -13 gene for artemisinin resistance or  exo - E415G  gene polymorphism and amplification in  plasmepsins 2  and  3  for piperaquine resistance were observed. In vitro testing of patient’s falciparum parasites indicated susceptibility (low IC 50  nM values) to dihydroartemisinin, lumefantrine, piperaquine and pyronaridine. Patient’s drug exposure to artesunate and lumefantrine was comparable to published data, however, blood CQ concentrations were lower.    Conclusions  Clinical findings, molecular analysis and in vitro testing revealed that the falciparum parasites at Phuoc Chien Commune were artemisinin susceptible. The clinical failure rate of the 15 vivax patients who completed CQ treatment was 13%. Further studies are required to determine whether CQ-resistant vivax malaria is present at the commune.    Electronic supplementary material  The online version of this article (10.1186/s12936-019-2640-2) contains supplementary material, which is available to authorized users.

malaria journal

Susceptibility of Plasmodium falciparum to artemisinins and Plasmodium vivax to chloroquine in Phuoc Chien Commune, Ninh Thuan Province, south-central Vietnam