title: Monitoring of clinical efficacy and in vitro sensitivity of Plasmodium vivax to chloroquine in area along Thai Myanmar border during 2009-2010.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Pharmacology and Toxicology Unit, Graduate Program in Biomedical Sciences, Thammasat University, Thailand.
authors.forename: Poonuch
authors.initials: P
authors.lastname: Muhamad
authors.forename: Ronnatrai
authors.initials: R
authors.lastname: Ruengweerayut
authors.forename: Wanna
authors.initials: W
authors.lastname: Chacharoenkul
authors.forename: Kanchana
authors.initials: K
authors.lastname: Rungsihirunrat
authors.forename: Kesara
authors.initials: K
authors.lastname: Na-Bangchang
mesh_terms: D000293:Adolescent; D000328:Adult; D000962:Antimalarials / Q000494:pharmacology / Q000627:therapeutic use; D002738:Chloroquine / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use; D004338:Drug Combinations; D004351:Drug Resistance; D005260:Female; D006801:Humans; D016780:Malaria, Vivax / Q000097:blood / Q000188:drug therapy*; D008297:Male; D008875:Middle Aged; D021261:Parasitic Sensitivity Tests; D010966:Plasmodium vivax / Q000187:drug effects*; D011319:Primaquine / Q000494:pharmacology / Q000627:therapeutic use*; D012036:Refugees; D013785:Thailand; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D000962:Antimalarials; D004338:Drug Combinations; C023676:chloroquine diphosphate; D002738:Chloroquine; D011319:Primaquine