Background: Chloroquine (CQ) is the first-line treatment for vivax malaria in Ethiopia, but there is evidence for its declining efficacy. Defining the extent and regional distribution of CQ resistance is critical to ensure optimal treatment guidelines. This study aimed to provide data on the therapeutic efficacy of CQ against Plasmodium vivax malaria in southern Ethiopia.
Methods: Patients with P. vivax mono-infection aged between 8 months and 65 years were enrolled in a clinical efficacy trial. The study was conducted at four sites in southern Ethiopia. Study participants were treated with a supervised course of CQ (25 mg/kg over three consecutive days), followed by weekly blood film examination and clinical assessment for 28 days. CQ blood concentrations were not assessed. The primary endpoint was the risk of failure at 28 days by survival analysis.
Results: Between May 2010 and December 2013, 288 patients were enrolled in the study (n = 89 in Shele, n = 52 in Guba, n = 57 in Batu and n = 90 in Shone). Baseline characteristics varied significantly between sites. In total 34 (11.8%) patients were censored during follow up (five with Plasmodium falciparum parasitaemia and 29 lost to follow up). Two (0.7%) patients experienced early treatment failure and 23 (8%) late treatment failure. The overall risk of recurrence by day 28 was 9.4% (95% CI 6.4-13.6%) with site-specific estimates of 3.8% (95% CI 1.2-11.3) for Shele, 21.9% (95% CI 12.2-36.1) for Guba, 5.9% (95% CI 1.9-17.3) for Batu and 9.2% (95% CI 4.5-17.6) for Shone.
Conclusion: There is evidence of reduced CQ efficacy across three of the four study sites, with the degree of resistance severe enough in Guba to suggest that review of treatment policy may be warranted.