[Ca++ ion transport blockers as reversants of the drug resistance of malarial parasites. 2. The effect of praziquantel on the resistance to chloroquine and compound R-70-Zh of Plasmodium berghei].

The reversing action of anthelminthic praziquantel (P) on the effect of chloroquine (C) and compound R-70-Zh (styrylquinazoline) was revealed on a Plasmodium berghei model (white inbred mice), using a LNK65 isolate with naturally reduced sensitivity to chloroquine and its polyresistant line LNK65CHLFR with acquired resistance to chloroquine/fansidar (selected in our laboratory). P (125 mg/kg) in combination with C showed a potentiating effect not only on the LNK65 isolate, but also on the LNK65CHLFR line, while investigated separately on this line, both drugs were not effective in tested doses. Moreover, the similar effect of C on the LNK65CHLFR line was achieved in the dose that was 4 times higher than that of P/C combination. P in a standard dose on the LNK65 isolate showed a more marked activation of compound R-70-Zh that on C. The potentiating effect was manifested in combination with R-70-Zh in the dose half as high as that of C; this phenomenon was also reflected by the efficiency index (5.0 against the 4.0) accepted in our laboratory and may be associated with the higher sensitivity of the LNK65 isolate to R-70-Zh. P showed some antimalarial action which manifested itself only by morphological changes on P. berghei parasites similar to those observed under the action of some dihydropholate reductase inhibitors, such as pyrimethamine.