The Vivax and Ovale Paediatric Primaquine Efficacy Study Group was created as an extension of the Vivax Primaquine Efficacy, Safety and Tolerability Study Group formed in August 2019. The manuscript ‘Primaquine for uncomplicated Plasmodium vivax malaria in children younger than 15 years: a systematic review and individual patient data meta-analysis’ was published in Lancet Child and Adolescent Health in September 2024.

Primaquine, an 8-aminoquinoline (8-AQ), is the only widely available antimalarial that kills dormant liver stages (hypnozoites) of Plasmodium vivax and Plasmodium ovale. Plasmodium vivax remains widespread and is becoming the predominant cause of malaria outside of Africa and is expected to be a greater obstacle to malaria elimination than Plasmodium falciparum.

The main burden of malaria is in young children and yet there is no suitable paediatric formulation available. Reliance on the adult tablet formulation may result in inaccurate paediatric dosing, and thus have a higher risk of adverse events and lower efficacy in preventing P. vivax recurrence.

Whilst primaquine is highly efficacious against hypnozoites and gametocytes, it can cause severe drug-induced haemolysis in individuals with G6PD deficiency. The risk of haemolysis depends on the duration and dose of primaquine administration, which is almost 20-fold higher for P. vivax radical cure than the single low dose administered for P. falciparum gametocytocidal activity. At high doses, primaquine induces gastro-intestinal symptoms that often reduce patient adherence.

Since its introduction into clinical practice more than 60 years ago there is a wealth of data from clinical trials documenting the safety and efficacy of primaquine in patients with P. vivax malaria, but relatively limited data in P. ovale malaria. Individual patient data (IPD) meta-analyses ensure the best use of available data from which to generate evidence that will inform improved dosing regimens with a new, clinically relevant, age-appropriate formulation. A paediatric formulation will result in improved safety, tolerability, efficacy, and adherence. 

1. To assess efficacy in terms of the prevention of P. vivax / P. ovale recurrence between day 7 and days 90 or 180 in children (<15 years) and how this relates to total dose of primaquine
2. To assess if the relationship between total primaquine dose and the incidence risk of P. vivax (or P. ovale) recurrence between day 7 and days 90 or 180 differs for young children, older children and adults

• Prospective clinical efficacy studies of uncomplicated vivax or ovale malaria with a minimum 42 days follow up:
  • Treatment with chloroquine or one of four common artemisinin-based combination therapies (artemether-lumefantrine, artesunate-mefloquine, artesunate-amodiaquine, dihydroartemisinin-piperaquine)
  • At least one treatment arm with primaquine given over multiple days and commencing within seven days of blood schizontocidal treatment
  • Study includes at least one patient aged under 15 years
  • Information on dose of schizontocidal treatment
  • Information on use, timing and dose of primaquine
• Study meta-data as described in the Clinical Data Management and Statistical Analysis Plan
• Baseline data on patient age and sex
• Parasite density at day 0 and presence or absence during follow up

• Baseline weight
• Individual primaquine dosing data (mg/kg dose; actual dose times; treatment supervision)
• Individual schizontocidal dosing data (mg/kg dose; actual dose times; treatment supervision)
• Nutritional status according to weight/ height/ middle upper arm circumference
• Qualitative or quantitative assessment of G6PD status
• CYP2D6 genotype/phenotype
• Haemoglobin or haematocrit at enrolment
• Outcome of malaria treatment according to standardized WHO/CDISC criteria
• Any concomitant medication documented

After upload to the WWARN Data Repository, WWARN standardised data sets according to the WWARN Clinical Data Management and Statistical Analysis Plan and pooled all primary data sets into a single database of quality-assured individual patient data.

The interaction between age and the total primaquine mg/kg dose and the duration of the primaquine regimen on the risk of recurrence was explored by multivariable Cox regression analysis. Subgroup analyses were undertaken within the paediatric population to compare i) children 1 year to less than 5 years versus children 5 to 15 years old and, ii) G6PD deficient versus G6PD normal paediatric patients (genotype and/or phenotype) 

Additional analyses explored the interaction between age and primaquine mg/kg dose and the duration of the primaquine regimen on incidence rate of recurrence (events per person years) in studies in which patients were followed for 6 months or more through multiple episodes of malaria.

A detailed statistical analysis plan was developed and shared with all contributors.

The Vivax and Ovale Paediatric Primaquine Efficacy Study Group comprised participating investigators who contributed relevant data sets to the pooled analysis. Participating investigators were recognised in publications as contributors under the banner of the Study Group. A Writing Committee coordinated activities, undertaking the data analysis and preparation of the reports and publications for review by the study group. Authors will be recognised according to the ICMJE guidelines and the WWARN publication policy.

For further information, please contact Rob Commons on email: rob.commons@wwarn.org

Vivax and Ovale Paediatric Primaquine Study Group: Primaquine for uncomplicated Plasmodium vivax malaria in children younger than 15 years: a systematic review and individual patient data meta-analysis. Lancet Child and Adolescent Health, 2024.