Chloroquine susceptibility of Plasmodium falciparum in Haiti.

In January and February 1982, in vivo and in vitro studies of the chloroquine sensitivity of Plasmodium falciparum were conducted in Port-au-Prince, Haiti. Of 19 infections tested in vivo using the WHO extended test, all but one were susceptible to the drug; the remaining case showed a recurrence of parasitaemia on day 28. Of the 19 corresponding 48-hour in vitro tests, 16 provided interpretable results; 12 tests demonstrated sensitivity to the drug, while in the remaining 4, parasite multiplication was inhibited only at drug concentrations higher than that previously accepted as indicative of sensitivity. (These four included the isolate from the patient who had a recurrence of parasitaemia on day 28.) While these results provide no absolute demonstration of chloroquine resistance, they underline the need for close monitoring of the susceptibility to chloroquine of P. falciparum in Haiti.