Interaction between chloroquine and diverse pharmacological agents in chloroquine resistant Plasmodium yoelii nigeriensis.

The effect of a number of pharmacological agents on the enhancement of antimalarial activity of chloroquine was evaluated against chloroquine resistant line of Plasmodium yoelii nigeriensis (N-67). The response after combination therapy was monitored on the basis of alteration in the course of parasitaemia, the extension of mean survival time and the percent cure rate in different groups. The study was designed to compare the in vivo efficacy of a number of resistance modulating agents found effective in several in vitro studies against chloroquine resistant P. falciparum isolates. Based on their efficacy in this rodent model, the response of combination of chloroquine with agents representing diverse chemical moieties has been categorised as curative, moderately active and inactive. Out of the 22 agents evaluated, only cyproheptadine-chloroquine combination produced curative response. Ketotifen, azatadine, pheniramine, amitriptyline, fluoxetine, verapamil, penfluridol and trifluoperazine demonstrated moderate activity while loratadine, terfenadine, promethazine, ranitidine, nifedipine, diltiazem, chlorpromazine, amiodarone, tamoxifen, dipyridamol, propranolol, acyclovir and amantidine were inactive. The study advocates the suitability of proposed rodent model to shortlist potential resistance reversal agents.