SURVEY OF RESISTANCE TO CHLOROQUINE BY PLASMODIUM-VIVAX IN INDONESIA

In February 1995 we surveyed resistance to chloroquine among patients with Plasmodium vivax malaria at Nias Island, in the Indian Ocean near north-western Sumatra, Indonesa. The subjects, 21 indigenous males an d females (6-50 years old) infected with >40 asexual blood stage paras ites of P. vivax per mu l of blood, had mild symptoms or none at all. Seven of these patients had >100 ng/mL whole blood chloroquine levels before the first supervised dose of chloroquine (3 doses of 10 mg/kg, 10 mg/kg, 5 mg/kg of base given at 24 h intervals). Whole blood chloro quine levels on the last day of dosing confirmed normal absorption (ra nge 413-3248, mean 1141, so 616 ng/mL). Blood films were examined on d ays 0, 2, 4, 7, 11, 14, 18, 21 and 28 after initiating therapy. Three patients had recurrent asexual P. vivax parasitaemias between days 14 and 18, despite effective levels of chloroquine in whole blood (greate r than or equal to 100 ng/mL) at the time of recurrence. Resistance to standard chloroquine therapy by P. vivax appeared in 14% of infection s among residents of Nias.