Treatment of vivax malaria on the western border of Thailand.
Luxemburger C., van Vugt M., Jonathan S., McGready R., Looareesuwan S., White NJ., Nosten F.
The efficacy of chloroquine (25 mg base/kg over 3 days) in Plasmodium vivax malaria was evaluated in 1995/96 in 342 patients living in an endemic area on the western border of Thailand. Clearance of fever and parasites was obtained within 2 days in > 95% of the patients, and all were aparasitaemic by day 4. Reappearance of P. vivax occurred in 1 patient on day 21 and in 8 by day 28, giving a 28-day cure rate of 97% [95% confidence interval (CI) 95-99%]. By day 63, the relapse/re-infection rate was 63% (95% CI 57-69%). Most reappearances of parasitaemia (85%; 121/143) were symptomatic. These patients were retreated either with chloroquine alone (n = 70) or with chloroquine and primaquine (0.25 mg/kg daily for 14 days) (n = 43). Only 1 patient (in the chloroquine-only group) had prolonged parasite clearance (D8) and he developed recurrent P. vivax by day 21 suggesting possible recrudescence. The addition of primaquine to chloroquine reduced the risk of having a third vivax episode within 2 months by 96% (95% CI 83-99%). This resulted in a significantly higher haematocrit at day 42 despite a greater decrease in haematocrit during the first week of treatment with chloroquine-primaquine (P = 0.04). Chloroquine remains highly effective on the western border of Thailand and the use of strictly supervised primaquine effectively prevents relapse. The introduction of primaquine on a large scale in an endemic area still requires a long-term risk-benefit assessment which must take into account potential toxicity, low compliance and reductions in the incidence and severity of P. falciparum infections by co-existent P. vivax.