In vivo and in vitro sensitivity of Plasmodium falciparum to chloroquine at Lubwe and Kalene in Zambia: use of amodiaquine as an alternative antimalarial drug.

The response of Plasmodium falciparum to chloroquine in Zambia was determined by the in vivo and in vitro microtechniques. A total dose of 25mg chloroquine base/kg body weight (over 3 d) was administered to 60 children at Lubwe and 42 at Kalene. The in vivo test was successfully completed on 55 cases at Lubwe and 39 at Kalene, chloroquine resistance being detected in 43.6% and 10.3% of the cases respectively. Out of the 32 successful in vitro microtests conducted at Lubwe and 28 at Kalene, schizont maturation at chloroquine concentrations greater than or equal to 5.7 pmol/well was observed in 81.3% of the isolates at Lubwe and 60.7% of those at Kalene. Most of the resistant isolates at both localities exhibited high minimum inhibitory concentrations (MICs): 44% of those at Lubwe had MICs greater than or equal to 32 pmol/well (6.4 mumol/litre), while 42.8% of those at Kalene had MICs of 16 pmol/well (3.2 mumol/litre). Amodiaquine administered in the recommended dose of 25mg/kg body weight over 3 d failed to clear asexual parasitaemia in 15.4% and 15.8% of the cases at Lubwe and Kalene respectively; mean parasite clearance times were 1.9 and 2.2 d. The usefulness of amodiaquine as a second-line drug for the treatment of malaria in Zambia is discussed.