The regimens used to compare the PQ 0.5 mg/Kg/day for 7 or 14 days were heterogeneous; three studies used an arm without PQ for comparison (19,22,23), out of these, two used CQ 25 mg/Kg as blood schizonticide (19,22) and one used artesunate (23); four studies used the standard regimen of PQ for comparison and CQ was also used in them (15,17,19,20), PQ 0.75 mg/Kg/week during 8 weeks was used in another one (22), while lower doses of PQ than standard regimen were used in the remaining studies (16,18,21).
Considering that recurrences can occur in less than 28 days after the primary episode (3-5), it is possible that some studies were omitted; however, we limit the systematic revision of studies with a follow-up longer than 28 days since most treatment regimens used for P vivax malaria use at least one long half-life blood schizontocidal such as chloroquine; and generally the therapeutic response to them is assessed during the first post-treatment month (7,8,26); therefore we did not include these studies in order to avoid an overestimation of the incidence of recurrences that could be caused by a recrudescence of blood parasites (blood schizonticide therapeutic failure) and not due to the lack PQ efficacy.
Artesunate is a semisynthetic derivative of artemisinin consisting of sodium succinyl salt of dihydroartemisinin, a potent blood schizonticide
highly effective against multidrug resistant strains of P falciparum.
It is a potent blood schizonticide
with a minimum inhibitory concentration of [10.sup.-7] M (De Vries and Dien, 1996).
Drugs acting at this site, known as 'tissue schizonticides
', prevent the infection and only need to be taken for 7 days after leaving the area (e.g.
Obaldia N, Rossan RN, Cooper RD, Kyle DE, Nuzum EO, Rieckmann KH, Shanks GD (1997) WR 238605, chloroquine, and their combinations as blood schizonticides
against a chloroquine-resistant strain of Plasmodium vivax in Aotus monkeys.
Relapses are not prevented by the blood-stage schizonticides
typically used for disease prevention, and these agents can actually mask the initial symptoms of infection, the investigators noted (N.