In-vivo resistance of Plasmodium falciparum to chloroquine and amodiaquine in south Cameroon and age-related efficacy of the drugs.

. Chloroquine resistance of Plasimdiam falciparum ( O F ) was first observed in Cameroon in 1985, in the south-west of the country, a region which is hyperendemic for malaria (Sansonetti et al., 1985). Although such resistance has since spread rapidly throughout the country (Louis et al., 1992; Basco et al., 1993), chloroquine still remains the most widely used antimalarial drug. Most of the information collected by the local Ministry of Health on CRPF is biased because it comes from studies in schoolchildren, in whom the immune response is likely to complement the action of drugs, by clearing parasites from the blood (Targett, 1992). Studies must also be conducted among other groups, particularly of children aged <5 years and pregnant women, if (1) the public-health problem posed by CRPF is to be fully addressed and (2) control measures and treatment policies are to be effective. A study to assess how the efficacy of chloroquine and amodiaquine varied with the age of the subject treated was therefore conducted in Ebolowa, a town with about 35 O00 inhabitants, in South Cameroon, 160 km south of Yaounde. T h e region is characterised by an equatorial climate. Although rain falls all year round (with an annual total of about 1700 mm), it is heaviest between September and December and between April and June. This pattern allows sites suitable for the breeding of anopheline mosquitoes to persist throughout each year and transmission of Plnsmodium spp. is perennial in the region. Health services in Ebolowa are provided by one state, provincial hospital (Ekombitie Hospital), one missionary hospital (EPC Enongal Hospital) and state or missionary health centres. Oral chloroquine is the current first-line treatment for uncomplicated malaria, whereas intramuscular or intravenous injections of quinine are used for severe malaria. Most (59.8%) of the families of the subjects investigated declared that they used drugs for the prevention of malaria, most (95%) of these using chloroquine. However, only 16% of the mothers interviewed gave a dose of chloroquine to their children which was large enough to be considered effective even against non-resistant malaria. Overall, 250 infants (12-24 months), 120 young children (36-60 months) and 600 schoolchildren (5-1 5 years) were screened for malaria by examination of Giemsa-stained blood smears. The schoolchildren, from one district of Ebolowa, were screened in April 1995 and the younger children, from Ebolowa or its surroundings, were screened monthly between September and December 1994. The 192 children enrolled for further study were the asymptomatic subjects who had > 1000 P. falciparuiiz parasites/pl blood but had not taken any treatment within 3 days of the initial examination. Each enrolled child was given a total of 25 mg chloroquine or amodiaquine/kg over 3 days (10, 10 and 5 mg/kg on days O, 1 and 2, respectively). Each dose was administered as tablets (of 100 mg chloroquine or 200 mg amodiaquine) under the supervision of a team member. The initial aim was to give chloroquine to three of every four schoolchildren as they enrolled and to two of every three of the younger children (the other children receiving amodiaquine). However, as 23 children were lost to follow-up, the final ch1oroquine:amodiaquine ratios were slightly different. The in-vivo response of the P. falciparzinz parasites in each subject was assessed using a slightly modified í'-day test (BruceChwatt, 1986). Thick, Giemsa-stained blood smears were prepared from each subject on days 3 and 7. Parasitaemias were then estimated by counting the parasites/200 leucocytes (positives) or 1000 leucocytes (negatives)