Resistance of Plasmodium falciparum to antimalarial drugs in a highly endemic area of southern Viet Nam: a study in vivo and in vitro

To assess the antimalarial sensitivity of Plasmodium falciparum in vivo and in vitro in a highly endemic area of southern Viet Nam, a field study was conducted (in 1999) at a rubber plantation in Binh Phuoc Province north of Ho Chi Minh City. Fifty patients were treated with either artesunate (4 mg/ kg on day 0, then 2 mg/kg on day 1 to 4) or mefloquine (10 mg/kg at 0 h, th en 5 mg/kg at 6 h), and their progress was followed for 28 days under stand ard WHO protocols. Blood spots were taken at baseline from all patients, as well as from those who redeveloped parasitaemia during follow-up, for poly merase chain reaction (PCR) determination of parasite genotypes to assist d ifferentiation of re-infection from recrudescence. Both treatments cleared parasites within 5 days. Of the 25 mefloquine-treated patients, 2 (8%) re-p resented with probable re-infections. For artesunate, 4 patients (16%) had re-infections and 5 (20%) had recrudescences. Sensitivity tests ira vitro o f pre-treatment P. falciparum isolates showed geometric mean ICS values of 29, 38, 209 and 15 nmol/L for chloroquine (n = 32), mefloquine (n = 33), qu inine (n = 31) and artemisinin (n = 31), respectively. There were significa nt correlations between IC(50)s for artemisinin and mefloquine (r = 0.72, P = 0.004), and chloroquine and quinine (r = 0.44, P = 0.05). These data sho w that, although mefloquine has been used for 10 years in Binh Phuoc Provin ce, it remains fully effective, perhaps because an artemisinin derivative i s commonly given at the same time. The recrudescence rate for artesunate is similar to those reported in other epidemiological contexts. The present i n-vitro data imply that quinine remains effective and that reduced drug pre ssure has been associated with increased sensitivity of local strains of P. falciparum to chloroquine. Although from one hyperendemic area, these resu lts may have implications for antimalarial prophylaxis and treatment strate gies for residents and travellers to southern Viet Nam.