P. vivax infections contribute to a significant proportion of the malaria infections in many Asian-Pacific and South American countries. Primaquine is the most frequently used drug for treating the dormant liver stage of the infection and is given in combination with chloroquine. Different primaquine dosing regimens are used to prevent relapses of the disease. The review included nine randomized controlled trials, comparing either primaquine plus chloroquine with chloroquine or the 14-day primaquine plus chloroquine regimen with a 5-day primaquine plus chloroquine regimen.
Compared with chloroquine alone, primaquine (for five days) plus chloroquine was no better in preventing relapses of P. vivax infection, while primaquine (for 14 days) plus chloroquine resulted in significantly fewer relapses. The 14-day primaquine regimen was also significantly better than the five-day primaquine regimen at preventing relapses. Adverse effects were poorly reported; three trials reported skin rash, vertigo, headache, abdominal pain and/or nausea in some participants, and two trials reported that primaquine was well tolerated.
Since the five-day primaquine plus chloroquine does not prevent relapses, countries should follow the World Health Organization's recommendation of the 14-day primaquine plus chloroquine regimen.