Short-Course Low-Dose Primaquine for Radical Cure in G6PD-Normal Patients in the Pre-Elimination Context of Nepal

Plasmodium vivax remains a challenge for malaria elimination in Nepal due to its ability to relapse. Radical cure with primaquine is effective but limited by poor adherence to the standard 14-day low-dose regimen. In 2022, the WHO recommended administering the same total dose (3.5 mg/kg) over 7 days to improve adherence. This study aimed to evaluate the 7-day low-dose primaquine regimen in G6PD-normal patients with uncomplicated P. vivax and/or P. falciparum malaria in the pre-elimination context of Nepal.

A randomised study was conducted in south-west Nepal. Adult patients with microscopically confirmed P. vivax and/or P. falciparum malaria and glucose-6-phosphate dehydrogenase (G6PD) activity ≥ 30% were randomised 1:1 to receive either a 7-day low-dose primaquine regimen (0.5 mg/kg/day; total 3.5 mg/kg) or standard of care (14-day primaquine [0.25 mg/kg/day; total 3.5 mg/kg] for patients with P. vivax malaria and single-dose primaquine for P. falciparum malaria patients) in addition to their schizonticidal treatment. All treatment was directly observed, and patients were followed for 6 months. The primary outcome was the risk of P. vivax recurrence at 6 months. Safety outcomes included adverse events, gastrointestinal symptoms and haematological parameters.

Of 5842 individuals screened, 27 eligible participants were enrolled. Among these, 21 had P. vivax, four had P. falciparum and two had mixed infections. Eleven participants had intermediate G6PD activity (≥ 30%-70% activity). At 6 months there were no recurrences in the 7-day primaquine arm (n = 14) and the risk of P. vivax recurrence in the standard primaquine arm (n = 13) was 9.1% (95% CI: 1.3-49.2). No participants vomited study drugs, and gastrointestinal symptoms were infrequent. Three participants experienced a ≥ 25% haemoglobin drop between baseline and Day 2, all of whom had baseline values > 15 g/dL. No presentations of haemoglobinuria, severe anaemia, serious adverse events, or deaths occurred during the study period.

In this small study, the 7-day low-dose primaquine regimen was well tolerated, including among individuals with intermediate G6PD activity. Although the small sample size limits conclusions about efficacy, the findings support the feasibility and safety of this regimen in Nepal, offering potential programmatic advantages for radical cure delivery in a setting close to elimination.

Clinicaltrials.gov: NCT04079621.