Primaquine Double Dose for Radical Cure of Plasmodium Vivax in Colombia

Malaria due to Plasmodium vivax (P. vivax) is still a public health challenge in the Americas. In recent years, the rate of decline in the incidence of P. vivax malaria has stalled in the Americas. To address this challenge and support countries in Latin America & the Caribbean (LAC) aiming for malaria elimination, effective treatment strategies against P. vivax are needed. Primaquine (PQ) is the only widely available treatment to prevent P. vivax relapses. WHO recommends increased PQ doses in East Asia and Oceania, where strains are frequently-relapsing. In 2005, the Centers for Diseases Control and Prevention (CDC) began also recommending higher dose PQ to treat infections from all parts of the world.

In Latin America, PQ for a radical cure has been largely implemented as 3.5 mg/kg over 14 days (standard dose, long-course, PQsd14) or 3.5 mg/kg over 7 days (short-course, or PQsd7) in combination with chloroquine (CQ). A recent randomized controlled trial in Brazil showed that a 7 mg/kg double dose regimen over 14 days (PQdd14) was superior in preventing relapses compared to the standard of care regimen in Brazil of 3.5 mg/kg over 7 PQsd7 Direct Observed Therapy (DOT) and PQsd7 without DOT and with or 14 days PQsd14 with DOT (92% versus 66% were relapse-free in the 6-month follow-up in adjusted analyses). These data were presented at the 2019 PAHO Malaria Technical Advisory Group (TAG) meeting.

To inform whether there should be a policy change by PAHO, the Malaria TAG recommended more evidence from the results of another trial to confirm the efficacy of high versus low-dose PQ. This project aims to generate the necessary evidence to inform a policy decision regarding high-dose PQ.

Impact Malaria (IM) proposes to conduct another trial, per the PAHO Malaria TAG's recommendation, assessing the efficacy of high-dose PQ compared to low-dose PQ. The objective is to compare a standard regimen, which in Colombia is PQsd14 (3,5mg/kg divided in 14 days), to a double dose alternative: PQ 7 mg/kg double dose regimen over 14 days (PQdd14).

PQ, the mainstay for a radical cure for P. vivax, induces a dose-dependent acute hemolytic anemia in individuals with Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency. Where available, WHO recommends G6PD deficiency testing prior to PQ administration. In LAC countries, where G6PD deficiency testing is not widely available, Low-dose PQ without G6PD deficiency testing has been a standard approach regimen for more than 60 years. Low prevalence of G6PD deficiency, a predominance of less severe variants, and the absence of historical reports of hemolysis with the 14-day Low-dose regimen have allowed for this unsystematic, standard approach without testing. Nevertheless, PAHO promotes pharmacovigilance and early recognition of signs of hemolysis to enable stopping PQ to prevent more severe outcomes. However, countries are not implementing these approaches systematically. Improved pharmacovigilance and G6PD deficiency testing may be needed if higher dose PQ regimens are recommended, as these regimens have a higher potential to cause severe hemolysis and other adverse events. Higher dose regimens may also be less well tolerated, and therefore compromise adherence. At the same time, where quality G6PD deficiency testing is not reliable or available, a risk-benefit assessment may suggest that the benefits of using high dose PQ without G6PD deficiency testing may still outweigh such risks.