Efficacy of chloroquine on Plasmodium falciparum transmitted at Amani, eastern Usambara Mountains, north-east Tanzania: an area where malaria has recently become endemic.

In order to assess the response of newly endemic falciparum malaria to currently used antimalarials, a field study was conducted in Amani, Tanzania. The efficacy of chloroquine (CQ) on Plasmodium falciparum was assessed by in-vivo and in-vitro methods. Fifty-four patients with pure falciparum malaria were treated with CQ and followed daily for 3 days and weekly for one month. Eighty-three per cent of infections exhibited some degree of in-vivo resistance to CQ (46% RI, 28% RII and 9% RIII). Pretreatment blood samples were obtained from all 54 patients for in-vitro sensitivity testing for CQ, amodiaquine (AQ), quinine (QN), and mefloquine (MQ). In-vitro data correlated well with in-vivo data; 80% of successful isolates were resistant to CQ. Forty-five per cent of successful isolates were resistant to AQ, 2% to QN, and none to MQ. The antimalarial levels yielding 99% inhibition (EC99) for CQ, AQ, QN, and MQ were 12.86, 3.24, 24.09 and 0.81 microM respectively. Urine HPTLC revealed CQ metabolites in 15% of study patients who denied recent CQ ingestion and had a negative Dill-Glazko test. This implies the high rate of CQ resistance observed in this study could be due in part to the widespread use of CQ for self-medication. Although the day 3 mean CQ plasma level was higher for sensitive and RI infections than for RII and RIII infections, the difference did not reach statistical significance. Our study results confirm that P. falciparum transmitted at Amani is highly resistant to CQ.