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M Sigrid Mac Donald-Ottevanger,1 Malti R Adhin,2 Jeetendra Kumar Jitan,3 Gustavo Bretas,4 Stephen GS Vreden1 1Foundation for Scientific Research Suriname (SWOS), 2Department of Biochemistry, Anton de Kom University of Suriname, 3Department of Public Health, Ministry of Health, Paramaribo, Suriname; 4Independent consultant, Rio de Janeiro, Brazil Background: Recurrent episodes of Plasmodium vivax are caused by dormant liver stages of the parasite, which are not eradicated by choloroquine. Therefore, effective treatment also includes the use of primaquine (PQ). However, this secondary preventive therapy is often not effective, mostly due to poor adherence to the relatively long treatment course, justifying a comparative study of the efficacy of different durations of PQ treatment. Materials and methods: We included patients presenting with an acute and documented P. vivax infection from January 2006 to February 2008. All patients received chloroquine 25 mg/kg over a 3-day period. Subsequently, patients in group 7D received PQ 30 mg/day for 7 days, and patients in group 14D received standard PQ 15 mg/day for 14 days. All doses were given under supervision and patients were followed up for at least 6 months. The Kaplan–Meier method was used to estimate cumulative probability of recurrence up to 12 months after treatment initiation stratified by treatment group. Cox regression was used to assess possible determinants for recurrent parasitemia. Results: Forty-seven of the 79 included patients (59.5%) were allocated to group 7D and 32 patients (40.5%) were allocated to group 14D. Recurrent parasitemia was detected in 31.9% of the cases in group 7D compared to 12.5% of the cases in group 14D (hazard ratio [HR] =3.36, 95% CI 1.11–10.16). Cumulative probability for recurrent parasitemia at 3, 6, and 12 months was 0.201 (95% CI 0.106–0.362), 0.312 (95% CI 0.190–0.485), and 0.424 (95% CI 0.274– 0.615) for group 7D and 0.100 (95% CI 0.033–0.279), 0.100 (95% CI 0.033–0.279), and 0.138 (95% CI 0.054–0.327) for group 14D, respectively. When adjusted for possible confounders, differences in recurrent parasitemia remained significant between the two regimens in Cox regression analysis. Conclusion: More than 30% of the patients receiving shorter treatment course had recurrent parasitemia, suggesting that the standard dose of 15 mg/day PQ for 14 days is more efficacious than 30 mg for 7 days in preventing P. vivax recurrent episodes. Furthermore, we suggest that P. vivax treatment in Suriname should be changed to PQ 30 mg/day for 14 days, as per Center for Disease Control and Prevention recommendation, in light of a recurrence rate of over 10%, even in group 14D. Keywords: malaria, vivax, recurrent episode, primaquine, treatment duration, efficacy