Monitoring of clinical efficacy and in vitro sensitivity of Plasmodium vivax to chloroquine in area along Thai Myanmar border during 2009-2010.

BACKGROUND: In Thailand, the proportion of Plasmodium vivax infection has become equal to Plasmodium falciparum. Reports of a trend of gradual decline of in vitro sensitivity of P. vivax to chloroquine in some areas of the country, together with accumulating evidences of chloroquine resistance P. vivax in other parts of the world, emphasize the need for closely and continuously monitoring clinical efficacy in conjunction with in vitro sensitivity of P. vivax isolates. METHODS: The study was conducted at Mae Tao clinic for migrant workers, Tak Province during March 2008-August 2009. A total of 130 patients (17 Thais and 113 Burmeses; 64 males and 66 females) with mono-infection of P. vivax malaria, aged between 15-60 years and weighing more than 40 kg, were included in the study. Patients received treatment with chloroquine (2,000 mg chloroquine phosphate over three days) and the anti-relapse drug primaquine (15 mg for 14 days). In vitro sensitivity of P. vivax isolates was evaluated by schizont maturation inhibition assay. RESULTS: All patients showed satisfactory response to treatment. The cure rate was virtually 100% within the follow-up period of 42 days. Neither recurrence of P. vivax parasitaemia nor appearance of P. falciparum occurred during the investigation period. In vitro data showed a stable sensitivity of chloroquine in this area since 2006. Geometric mean and median (95% CI) values of IC50 for chloroquine were 100.1 and 134.7 (1.1-264.9) nM, respectively. CONCLUSION: In vivo results suggest that the standard regimen of chloroquine was still very effective for the treatment of blood infections with P. vivax in the Thai-Myanmar border area. In vitro sensitivity data however, raise the possibility of potential advent of resistance in the future. Regular monitoring of the chloroquine sensitivity of P. vivax is essential to facilitate the early recognition of treatment failures and to expedite the formulation of appropriate changes to the drug policy.

Assessment of in vitro sensitivity of Plasmodium vivax fresh isolates.

OBJECTIVE: To compare the applicability of the SYBR Green-I assay with the standard schizont maturation assay, for determination of sensitivity of Plasmodium vivax (P. vivax) to chloroquine and a new antifolate WR 99210. METHODS: The study was conducted at Mae Tao Clinic for migrant workers, Tak Province during April 2009 to July 2010. A total of 64 blood samples (1 mL blood collected into sodium heparinized plastic tube) were collected from patients with mono-infection with P. vivax malaria prior to treatment with standard regimen of a 3-day chloroquine. In vitro sensitivity of P. vivax isolates was evaluated by schizont maturation inhibition and SYBR Green-I assays. RESULTS: A total of 30 out of 64 blood samples collected from patients with P. vivax malaria were successfully analyzed using both the microscopic schizont maturation inhibition and SYBR Green-I assays. The failure rates of the schizont maturation inhibition assay (50%) and the SYBR Green-I assay (54%) were similar (P=0.51). The median IC10s, IC50s and IC90s of both chloroquine and WR99210 were not significantly different from the clinical isolates of P. vivax tested. Based on the cut-off of 100 nM, the prevalences of chloroquine resistance determined by schizont maturation inhibition and SYBR Green-I assays were 19 and 11 isolates, respectively. The strength of agreement between the two methods was very poor for both chloroquine and WR99210. CONCLUSIONS: On the basis of this condition and its superior sensitivity, the microscopic method appears better than the SYBR Green-I Green assay for assessing in vitro sensitivity of fresh P. vivax isolates to antimalarial drugs.

Assessment of in vitro sensitivity of Plasmodium vivax fresh isolates

Objective: To compare the applicability of the SYBR Green-I assay with the standard schizont maturation assay, for determination of sensitivity of Plasmodium vivax (P. vivax) to chloroquine and a new antifolate WR 99210. Methods: The study was conducted at Mae Tao Clinic for migrant workers, Tak Province during April 2009 to July 2010. A total of 64 blood samples (1 mL blood collected into sodium heparinized plastic tube) were collected from patients with mono-infection with P. vivax malaria prior to treatment with standard regimen of a 3-day chloroquine.In vitro sensitivity of P. vivax isolates was evaluated by schizont maturation inhibition and SYBR Green-I assays. Results: A total of 30 out of 64 blood samples collected from patients withP. vivax malaria were successfully analyzed using both the microscopic schizont maturation inhibition and SYBR Green-I assays. The failure rates of the schizont maturation inhibition assay (50%) and the SYBR Green-I assay (54%) were similar (P=0.51). The median IC10s, IC50s and IC90s of both chloroquine and WR99210 were not significantly different from the clinical isolates of P. vivax tested. Based on the cut-off of 100 nM, the prevalences of chloroquine resistance determined by schizont maturation inhibition and SYBR Green-I assays were 19 and 11 isolates, respectively. The strength of agreement between the two methods was very poor for both chloroquine and WR99210. Conclusions: On the basis of this condition and its superior sensitivity, the microscopic method appears better than the SYBR Green-I Green assay for assessing in vitro sensitivity of fresh P. vivax isolates to antimalarial drugs.