Efficacy of chloroquine plus low-dose primaquine and pyronaridine–artesunate plus low-dose primaquine against Plasmodium vivax malaria in adults and transmission to mosquitoes in Ethiopia: a phase 2/3, observer-masked, randomised, parallel-group trial

Abstract

BACKGROUND: In areas co-endemic for Plasmodium vivax and Plasmodium falciparum, artemisinin-based combination therapy is being considered as unified treatment strategy. The clinical and transmission-reducing efficacy of antimalarials remain understudied for P vivax, particularly in Africa. In this study, we aimed to evaluate the in-vivo efficacy, safety, and tolerability of pyronaridine-artesunate and chloroquine, each combined with a 14-day low-dose primaquine regimen, to treat uncomplicated P vivax malaria in Ethiopia and to assess the gametocytocidal and transmission-blocking effects of pyronaridine-artesunate and chloroquine, with or without low-dose primaquine, through direct mosquito feeding assays. METHODS: Two parallel-group, observer-masked, randomised, phase 2/3 trials were conducted at two health centres (primary health-care units) in Maksegnit and Enfranz, Ethiopia, to evaluate the efficacy of chloroquine and pyronaridine-artesunate, each combined with low-dose primaquine, in adult febrile participants aged 18 years or older with microscopy-confirmed asexual P vivax malaria. Participants were randomly assigned 1:1 to receive either chloroquine plus low-dose primaquine or pyronaridine-artesunate plus low-dose primaquine using simple randomisation. Microscopists assessing outcomes were masked to treatment allocation. Clinical assessments and fingerprick blood collection for microscopy and molecular analysis were conducted on days 0-3 and weekly on days 7-42. The primary outcomes were adequate clinical and parasitological response (ACPR), assessed at day 28 in both chloroquine plus low-dose primaquine and pyronaridine-artesunate plus low-dose primaquine groups and at day 42 in the pyronaridine-artesunate plus low-dose primaquine group, analysed per protocol. Safety and tolerability were monitored in the intention-to-treat population throughout the 42-day follow-up period via clinician assessments and participant self-reports. In the transmission substudy, individuals carrying gametocytes, per microscopy detection, were recruited and randomly assigned to receive chloroquine or pyronaridine-artesunate, with immediate or delayed (day 3) low-dose primaquine administration. Mosquito infectivity was assessed before and on days 1-3 after treatment. The completed trial is registered at the Pan African Clinical Trials Registry (PACTR202110520435408). FINDINGS: Between Jan 3, and June 17, 2022, 176 participants (122 [69%] male and 54 [31%] female) were enrolled (88 per group), and 79 in the chloroquine group and 83 in the pyronaridine-artesunate group were included in primary outcome analyses. Day-28 ACPR was 98·7% (78 of 79; 95% CI 91·3-99·8) for the chloroquine plus low-dose primaquine group and 98·8% (82 of 83; 95% CI 91·7-99·8) for the pyronaridine-artesunate plus low-dose primaquine group; day-42 ACPR in the pyronaridine-artesunate plus low-dose primaquine group was 96·4% (80 of 83; 95% CI 89·2-98·8). The most common adverse events were mild and included headache (45 [51%] of 88 in the chloroquine group vs 49 [56%] in the pyronaridine-artesunate group), weakness (28 [32%] vs 25 [28%]), body pain (27 [31%] vs 25 [28%]), and chills (20 [23%] vs 23 [26%]). No serious adverse events or treatment-related deaths occurred. Both treatment regimens were well tolerated. 60 participants were enrolled in the transmission substudy during the same time period as the main treatment efficacy study; 55 (92%) participants were infectious to mosquitoes at baseline. By day 1, infectivity was completely blocked in 15 (100%) of 15 participants in the pyronaridine-artesunate plus low-dose primaquine group, but residual transmission was observed in the chloroquine (seven [47%] of 15), pyronaridine-artesunate (two [13%] of 15), and chloroquine plus low-dose primaquine groups (four [27%] of 15). No mosquito infections occurred on day 2 or day 3 in any group. INTERPRETATION: Both regimens treated P vivax malaria with high efficacy. Pyronaridine-artesunate plus low-dose primaquine rapidly interrupted transmission. The findings support further evaluation of pyronaridine-artesunate plus low-dose primaquine as a unified treatment strategy in co-endemic settings to improve malaria control and support malaria elimination efforts. FUNDING: US President's Malaria Initiative and Wellcome Trust.