Factors Affecting the Chloroquine and Primaquine Treatment Responses in Patients with Vivax Malaria in Korea

Abstract

Background: Vivax malaria is a protozoal infection caused by P. vivax. After re-emergence in 1993, about 500 - 600 patients have been occurring recently In South Korea. Chloroquine which is the blood schizonticide and primaquine which eliminate dormant hypnozoites in the liver are the standard therapeutic agents for vivax malaria. However, recent studies reported that the parasite clearance time (PCT) is being extended since 2010 in Korea. Moreover, there is growing concern about the emerging of chloroquine resistance of P. vivax which are repeatedly exposed to chloroquine due to massive chemoprophylaxis. Primaquine is metabolized by the enzyme cytochrome P450 isoenzyme 2D6 (CYP2D6) to change into an active metabolite having antimalarial properties. Recently, several studies have reported that the antimalarial properties of primaquine varies depend polymorphic CYP2D6 activity. In the case of 'poor metabolizer (PM)' or 'intermediate metabolizer (IM)', the therapeutic effect of the drug may not be significant because of the low level of primaquine metabolites even if appropriate dosage is administered. In this study, we identified host factors related to decrease chloroquine therapeutic efficacy and the prevalence of mutation in chloroquine resistance genes in the clinical isolated P. vivax from patients in Korea. In addition, we analyzed the CYP2D6 profiles of patients to identify the association between primaquine metabolization and recurrence of malaria. Methods: Vivax malaria patients were enrolled prospectively in 9 hospitals in Gyeonggi-do Province, Incheon and Seoul. Parasitemia more than 72 hours have been considered as decreased therapeutic efficacy to chloroquine, and clinical characteristics were compared between the two groups with and without P. vivax parasitemia at 72 hours after first dose of chloroquine. The prevalence of mutations in chloroquine resistance genes (pvmdr1 and pvcrt-o) in the clinical isolated P. vivax from patients were analyzed. To identify the relationship between CYP2D6 genotype and relapse of vivax malaria, the DNA from the blood samples of patients who were suspected recurred malaria were provided by the Korea Diseases Control and Prevention Agency (KDCA). The CYP2D6 genotype and phenotype of prospectively enrolled patients and recurred patients registered with the KCDA were analyzed and we compared the difference between recurred patients and non-recurred patients. Results: A total of 102 patients were enrolled prospectively during the study period, including one patient with four times of malaria attack. Additionally, the KCDA provided blood samples of 38 suspected recurred patients. The female sex was significantly associated with the prolonged parasitemia in univariable logistic regression analysis, not in multivariable analysis. When analyzed male patients by removing the sex factor, chloroquine total dose per body weight and the percentage of administration of less than 25 mg/kg of chloroquine were significantly different between the two groups. Univariable and multivariable logistic regression analysis did not show a significant association between chloroquine dose and prolonged parasitemia, however, the risk of prolonged parasitemia tended to decrease as the chloroquine total dose per body weight increased (hazard ration 0.57, 95% CI; 0.27 - 1.16; p = 0.12). The pvmdr1 analysis showed that mutations at amino acid position Y976F were not found but mutation at position F1076L was identified in all isolates. The overall frequency of K10 insertion in isolated from this study was 0%. When comparing the CYP2D6 phenotype and genotype between the recurred and non-recurred groups, risk of recurrence was statistically higher in the poor or intermediated metabolizer, than that of normal or ultrarapid metabolizer (OR = 2.33, p = 0.02). In case with genotype-determined activity score less than 1.5, risk of recurrence was statistically higher than in case with 1.5 or higher (OR = 2.65, p = 0.04). Conclusion: In this study, we determined that decreased treatment efficacy to chloroquine of vivax malaria may be associated with insufficient dosage of chloroquine, suggesting that it is important to administer an appropriate dosage of chloroquine based on the patient's body weight in clinical practice. Genetic polymorphism of the chloroquine resistance gene in P. vivax were not identified in this study, however, enhanced monitoring of decreasing chloroquine efficacy and the evaluation of detailed molecular mechanisms involved in drug resistance of P. vivax malaria is essential. Moreover, CYP2D6-dependent metabolism of primaquine may be a key determinant of anti-hypnozoite activity of primaquine that prevent P. vivax malaria relapse.