Evaluation of the paediatric dose of chloroquine in the treatment of Plasmodium vivax malaria

Background: Chloroquine (CQ) continues to be the first-line medication used worldwide in the treatment of Plasmodium vivax malaria. The dose recommended by the World Health Organization is 25 mg/kg independently of the age of the subject. Nonetheless, the pharmacokinetics and pharmacodynamics of drugs in children are different from those in adults and may influence the drug concentrations in blood and become risk factors for therapeutic failure and/o resistance to CQ. Methods: This study is a secondary analysis of the data from a clinical trial in which children over 5 years of age were administered 25 mg/kg of CQ, and CQ concentrations in blood were measured at day 7 of follow-up. Models of regression and comparison were used to evaluate and compare the CQ dose taken per kg/body weight, the CQ dose calculated based on body surface area, CQ levels in blood on day 7 and the age of the population. Results: The younger the study population the greater the difference between the dose per kg/body weight (real dose) and that calculated according to the BSA (theoretical dose). The difference between the two doses was -181.206 mg in the 5-9 years of age group (CI 95 % - 195.39; - 167.02 mg) and -71.39 mg (CI 95 % - 118.61; -23.99 mg) in the 10-14-year-old group. The CQ concentrations in blood on day 7 differed in patients over and under 15 years (p = 0.008). A negative correlation was found between the real and theoretical dose (difference in dose) and the age in years (R2 = 0.529, p = 0.001). A negative correlation was also found between the difference in dose (mg) and CQ concentrations on day 7 (ng/ml) (r = -0.337, p = 0.001). Children under 15 years were found to have a higher rate of therapeutic failure than those over 15 (28 vs 4.2 %, respectively) (Kaplan-Meier p = 0.005). Conclusions: A CQ dose of 25 mg/kg for the treatment of P. vivax malaria may be too low in children as demonstrated by the reduction in CQ concentrations in blood at day 7 of follow-up. This under-dosage is probably associated with the higher rate of therapeutic failure found in children under 15 years (28 vs 4.3 %). These results suggest the need to review the paediatric doses of CQ currently used.