Prospective observational study to assess the feasibility and safety of appropriate Plasmodium vivax radical cure with tafenoquine or primaquine after quantitative G6PD testing during pilot implementation in Thailand

Abstract

Introduction Plasmodium vivax recurrence prevention using tafenoquine or primaquine is critical for achieving Thailand’s malaria elimination targets. Both drugs may cause haemolysis in glucose-6-phosphate dehydrogenase (G6PD) deficient individuals. This study evaluated the operational feasibility and safety of administering tafenoquine or primaquine after quantitative G6PD point-of-care testing in Thailand. Methods This prospective, observational, multicentre, longitudinal study was conducted between 23 May 2022 and 14 September 2023 during pilot implementation at seven sites in Yala and Mae Hong Son provinces. Eligible patients were ≥16 years old with uncomplicated P. vivax malaria. G6PD enzyme activity was quantified using a point-of-care device. All patients received 3-day chloroquine plus (based on G6PD enzyme activity): single-dose tafenoquine 300 mg (≥6.1 U/g Hb), or primaquine 15 mg/day for 14 days (≥4.1 U/g Hb), or primaquine 45 mg/week for 8 weeks (≤4.0 U/g Hb), with follow-up on days 5 and 14. Hospital admissions were reviewed to confirm acute haemolytic anaemia cases. The primary endpoint was the percentage of P. vivax patients ≥16 years old treated or not treated with tafenoquine in accordance with G6PD enzyme activity. Results Of 316 P. vivax patients screened, 187 were enrolled. All patients completed quantitative G6PD testing. According to G6PD status, appropriate use or non-use was 100% (95% CI 97.2, 100 (132/132)) with tafenoquine, 100% (95% CI 96.5, 100 (104/104)) with daily primaquine and 99.5% (97.1, 100 (186/187)) with weekly primaquine. At day 5, adverse events possibly related to haemolysis occurred in 46.3% (37/80) of patients with tafenoquine, 56.8% (46/81) with daily primaquine and 77.8% (14/18) with weekly primaquine, with no confirmed drug-induced acute haemolytic anaemia cases. Conclusion Point-of-care quantitative G6PD testing prior to appropriate tafenoquine or primaquine administration was operationally feasible within the Thailand health system, with no concerning adverse events, supporting implementation of this treatment algorithm in areas of active P. vivax transmission.