Parasitological and clinical efficacy of standard treatment regimens against Plasmodium falciparum, P. vivax and P. malariae in Papua New Guinea.

Resistance of Plasmodium falciparum (Pf) and P. vivax (Pv) to standard antimalarials is widespread in Papua New Guinea (PNG). The objective of the study was to assess the rate of clinical treatment failure (TF) and parasite resistance to amodiaquine (AQ), chloroquine (CQ) and quinine+sulfadoxine/pyrimethamine (Q+SP) for malaria in a rural health centre of the East Sepik Province. 179 patients presenting with symptoms and signs of malaria and with Pf (144 patients), Pv (18 patients), P. malariae (Pm) (7 patients) or mixed infection (10 patients) were included. 86 were treated with AQ, 88 with CQ and 5 with Q+SP. 21/179 patients (12%) were not cured or had a recrudescence of symptoms associated with parasitaemia in the 28 days following treatment, 14% after AQ, 10% after CQ and 0% after Q+SP. The proportion of TF was higher (17%) when the analysis population included only the 108 subjects who had a complete follow-up, especially for failure with Pf following AQ treatment (26%). During the 28 days of follow-up, RII or RIII level of resistance in Pf was detected in 55% of the subjects treated with amodiaquine, 30% of those treated with chloroquine and 0% of those treated with quinine+SP. Of the Pv or Pm parasites only one Pv was found to be RII resistant to CQ in the 28-day test. In vitro resistance of Pf to CQ was higher than to AQ (50% versus 27% of 36 parasite samples that grew successfully). The level of TF and parasitological resistance to standard antimalarial drugs was lower in this area than in urban settings, where drugs are more easily available. AQ performed less well than CQ but the difference is likely to be due to the age of the users, ie, their level of immunity, AQ being the first-line drug for young children. These results provided support for the recent change in the policy for the standard treatment of uncomplicated malaria in PNG from AQ or CQ to the combination of AQ+SP or CQ+SP, a recommendation aimed at slowing down the spread of multidrug resistance.