A randomized trial conducted in Brazil was published in New England Journal of Medicine demonstrated the efficacy of three primaquine regimens to prevent relapse of P. vivax malaria in children and adults with microscopy-confirmed P. vivax monoinfection.

In group 1, 63 patients received a total primaquine dose of 3.5 mg per kilogram (0.5 mg per kilogram per day) over 7 days with unobserved administration. 96 in group 2 also received a total primaquine dose of 3.5 mg per kilogram (0.5 mg per kilogram per day) over 7 days with observed administration and 95 in group 3 received a total primaquine dose of 7.0 mg per kilogram over 14 days (also 0.5 mg per kilogram per day) with observed administration. Follow up was done for all patients for 168 days.

By day 28, two P. vivax recurrences occurred in group 1 and one in group 2. 70 recurrences were observed by day 168 with 24 in group 1, 34 in group 2, and 12 in group 3. No major side effects were reported.

The recurrence rate of Group 1, group 2 and group 3 were 58 percent, 59 percent, and 86 percent  respectively. The difference in the day 168 recurrence-free percentage between groups 1 and 3 was 27 percentage points while the difference between groups 2 and 3 was 27 percentage points.

The study found that a greater dose of primaquine (7.0 mg per kilogramme) was more efficient at preventing Plasmodium vivax malaria relapses. (MedPage Today March 31, 2022), N Engl J Med 2022; DOI: 10.1056/NEJMoa2104226.