Quinine and quinidine: a comparison of EKG effects during the treatment of malaria.

We recorded electrocardiograms from 31 patients receiving quinine and 14 patients receiving quinidine for the treatment of Plasmodium falciparum malaria. Despite plasma quinine concentrations of up to 20 mg/L, there was no evidence of cardiotoxicity. QT prolongation was considerably greater in the quinidine-treated patients. The mean ratio of change in corrected QT interval to change in plasma concentration (delta QTc%/delta CQ) was 3.2% . mg-1 . L-1 for quinidine, compared to 0.74% . mg-1 . L-1 for quinine (p less than 0.001). T-wave flattening was observed in both groups. Plasma concentrations of quinine cannot be predicted from the EKG, because concentrations within the therapeutic range produced only minor and unpredictable abnormalities.