Assessment of the response in vivo and in vitro of Plasmodium falciparum to sulphadoxine-pyrimethamine in the malarious areas of Iran.

Studies of drug resistance of Plasmodium falciparum cases from SE Iran were carried out in vivo and in vitro during 1990-91. In a study of 26 chloroquine-resistant infections, using amodiaquine (25 mg kg-1 over 3 days), followed by two-thirds of the standard dose of sulphadoxine-pyrimethamine, six cases were resistant at the RI(3) and RII(3) levels. An additional study testing the standard dose of sulphadoxine-pyrimethamine in 43 chloroquine-resistant cases revealed five (11.6%) resistant at the RI(2) and RII(3) levels. Six of the above resistant infections were contracted in Hormozgan, three in Sistan-Baluchestan, one in Kerman provinces of Iran and one in Pakistan. In five of 22 successful in-vitro tests, carried out on different isolates, the parasites grew to schizonts (> or = 8 nuclei) in the wells containing 1000 pmol sulphadoxine and 12.5 pmol pyrimethamine, indicative of resistance.