The risk of recurrent Plasmodium vivax malaria and haematological effect of treatment with or without primaquine: a systematic review and individual patient data meta-analysis

1.   A summary (study profile) of the relevant trials uploaded to the WWARN repository will be presented to highlight potential selection bias.2.   A summary of the relevant studies will be presented, including (but not restricted to) treatment tested, inclusion and exclusion criteria, follow up duration, study populations, parasitaemia sampling scheme and description of location by country, transmission site(s), regional relapse periodicity and chloroquine resistance. Tests of statistical significance will not be undertaken for baseline characteristics; rather the clinical importance of any differences in the baseline distributions will be noted.Baseline characteristics of patients:3.   A summary of relevant baseline patient characteristics will be presented including age, gender, malnutrition, treatment given, treatment supervision, timing of primaquine, G6PD status, haemoglobin concentration, asexual parasitaemia, gametocytaemia, temperature >37.5C, prior antimalarial use, prior malaria history.Summary statistics will be broken down by gender and age category. The distribution of continuous variables (e.g. mg/kg total drug dose for each dosing group) will be described using the mean and standard deviation if the data are normally distributed, geometric mean and 95% reference range if the data are normally distributed following a log transformation, or the median and interquartile range if the data are non-normally distributed.4.   Schizontocidal and primaquine treatment dosingA summary of the distribution of mg/kg primaquine dose, including daily mg/kg dose and duration.5.   Risk of PV recurrence within 365 dayso   Kaplan-Meier (K-M) estimates will be computed for the primaquine dosing groups. Log rank test stratified by study sites will be performed at 5% level of significance to test if the K-M profiles are significantly different from each other. o   The proportion of patients who failed will be presented. In addition, the median time to presentation with recurrent infection will be calculated for different age-groups.o   Median (IQR) mg/kg dose of primaquine in patients failing treatment (i.e. recurrence) vs successfully treated (defined as reaching the end of the study duration without failure) will be calculated.o   Cox regression analysis for time to recurrence during follow-up will be performed, with a random intercept for study-site. The efficacy analysis will be restricted to studies with follow up of 42 days or longer. Primaquine use, regimen and mg/kg dose will be controlled for potential confounders including age, sex, baseline parasitaemia, schizontocidal treatment and relapse periodicity. Weight will not be included due to collinearity with age. Collinearity between relapse periodicity and geographical region and parasite prevalence will be examined. Additional covariates will be examined including level of treatment supervision, vomiting, baseline temperature and haemoglobin.o Additional Cox regression analysis will be performed on studies with follow up of 28 days or longer to investigate the effect of adherence on risk of recurrence. Factors associated with poor adherence will then be identified.o Network meta-analysis methods will be used for comparisons of primaquine regimens that have not been compared directly within a single trial (i.e. indirect comparisons).Subgroup analyses will restrict data to: i) Patients treated with chloroquine    ii) Children <15 years   ii) Studies with a minimum 6 months of follow up    iii) Presence of symptomatic recurrence.6. Incidence rate of recurrence (events per person years) will be compared between primaquine treatment regimens in studies in which patients were followed for 6 months or more through multiple episodes of malaria. Primaquine use, regimen and mg/kg dose will be controlled for potential confounders including age, sex, baseline parasitaemia, schizontocidal treatment and relapse periodicity.7. Multivariable logistic regression analysis will be undertaken to investigate the effect of daily primaquine mg/kg dose on gastrointestinal drug tolerability, presence of additional adverse events and severe adverse events, including presence of haemolysis, anaemia and neutropenia. Linear mixed effects models with non-linear terms for time will be undertaken for methaemoglobin, and white cell count. Analyses will include studies in which patients were followed for 28 days or more, and will be stratified by age.8. Haemoglobin time profiles will be examined using linear mixed effects models with non-linear terms for time. Models will be used to identify differences in treatment regimens at key time-points.