Primaquine for uncomplicated Plasmodium vivax malaria in children younger than 15 years: a systematic review and individual patient data meta-analysis

Background Primaquine, the only widely available treatment to prevent relapsing Plasmodium vivax malaria, is produced as 15 mg tablets, and new paediatric formulations are being developed. To inform the optimal primaquine dosing regimen for children, we aimed to determine the efficacy and safety of different primaquine dose strategies in children younger than 15 years. Methods We undertook a systematic review (Jan 1, 2000-July 26, 2024) for P vivax efficacy studies with at least one treatment group that was administered primaquine over multiple days, that enrolled children younger than 15 years, that followed up patients for at least 28 days, and that had data available for inclusion by June 30, 2022. Patients were excluded if they were aged 15 years or older, presented with severe malaria, received adjunctive antimalarials within 14 days of diagnosis, commenced primaquine more than 7 days after starting schizontocidal treatment, had a protocol violation in the original study, or were missing data on age, sex, or primaquine dose. Available individual patient data were collated and standardised. To evaluate efficacy, the risk of recurrent P vivax parasitaemia between days 7 and 180 was assessed by time-to-event analysis for different total mg/kg primaquine doses (low total dose of similar to 3 center dot 5 mg/kg and high total dose of similar to 7 mg/kg). To evaluate tolerability and safety, the following were assessed by daily mg/kg primaquine dose (low daily dose of similar to 0 center dot 25 mg/kg, intermediate daily dose of similar to 0 center dot 5 mg/kg, and high daily dose of similar to 1 mg/kg): gastrointestinal symptoms (vomiting, anorexia, or diarrhoea) on days 5-7, haemoglobin decrease of at least 25% to less than 7g/dL (severe haemolysis), absolute change in haemoglobin from day 0 to days 2-3 or days 5-7, and any serious adverse events within 28 days. This study is registered with PROSPERO, CRD42021278085. Findings In total, 3514 children from 27 studies and 15 countries were included. The cumulative incidence of recurrence by day 180 was 51 center dot 4% (95% CI 47 center dot 0-55 center dot 9) following treatment without primaquine, 16 center dot 0% (12 center dot 4-20 center dot 3) following a low total dose of primaquine, and 10 center dot 2% (8 center dot 4-12 center dot 3) following a high total dose of primaquine. The hazard of recurrent P vivax parasitaemia in children younger than 15 years was reduced following primaquine at low total doses (adjusted hazard ratio [HR] 0 center dot 17, 95% CI 0 center dot 11-0 center dot 25) and high total doses (0 center dot 09, 0 center dot 07-0 center dot 12), compared with no primaquine. In 525 children younger than 5 years, the relative rates of recurrence were also reduced, with an adjusted HR of 0 center dot 33 (95% CI 0 center dot 18-0 center dot 59) for a low total dose and 0 center dot 13 (0 center dot 08-0 center dot 21) for a high total dose of primaquine compared with no primaquine. The rate of recurrence following a high total dose was reduced compared with a low dose in children younger than 15 years (adjusted HR 0 center dot 54, 95% CI 0 center dot 35-0 center dot 85) and children younger than 5 years (0 center dot 41, 0 center dot 21-0 center dot 78). Compared with no primaquine, children treated with any dose of primaquine had a greater risk of gastrointestinal symptoms on days 5-7 after adjustment for confounders, with adjusted risks of 3 center dot 9% (95% CI 0-8 center dot 6) in children not treated with primaquine, 9 center dot 2% (0-18 center dot 7) with a low daily dose of primaquine, 6 center dot 8% (1 center dot 7-12 center dot 0) with an intermediate daily dose of primaquine, and 9 center dot 6% (4 center dot 8-14 center dot 3) with a high daily dose of primaquine. In children with 30% or higher glucose-6-phosphate dehydrogenase (G6PD) activity, there were few episodes of severe haemolysis following no primaquine (0 center dot 4%, 95% CI 0 center dot 1-1 center dot 5), a low daily dose (0 center dot 0%, 0 center dot 0-1 center dot 6), an intermediate daily dose (0 center dot 5%, 0 center dot 1-1 center dot 4), or a high daily dose (0 center dot 7%, 0 center dot 2-1 center dot 9). Of 15 possibly drug-related serious adverse events in children, two occurred following a low, four following an intermediate, and nine following a high daily dose of primaquine. Interpretation A high total dose of primaquine was highly efficacious in reducing recurrent P vivax parasitaemia in children compared with a low dose, particularly in children younger than 5 years. In children treated with high and intermediate daily primaquine doses compared with low daily doses, there was no increase in gastrointestinal symptoms or haemolysis (in children with 30% or higher G6PD activity), but there were more serious adverse events.