A REASON FOR INDIVIDUAL DIFFERENCES IN RESPONSE TO QUINIDINE?

16 % of 42 patients on quinidine bad concentrations of the metabolite OS).J-hydroxyquinidine (J-OH) in serum water higher than

that of quinidine. Since J'()H has similar antiarrhythmic activilY to quinidine. this metabolite may have a significant effect in SQme patients on quinidine, contributing to the individual differences in dose-response relationsrups. Results from the 42 patients were pooled with those of 25 other patients reported previously. The J-OH / quirudine ratio averaged 0.34 (range O. 10-0.90), I I patients had ratios above 0.50. Aner adjusting for average protein binding differences between the 2 compounds. the J-OH concenlJ'ations in serum water for these patients exceeded those of quinidine. Another 7 patients (10 %) had serum water 3.()H levels slightly below those of quinidine - 3-OH Iquinidine ratios 0.40-0 .50. Quinidine clearance in the study patients decreased with -age (r '"' 0.50), indicating a need for smaller doses, on average, in elderly cardiac patients and higher doses inchiJdren. Dl1Iyer, D.E. et al .: QirtiaJ Pttarrnacoloey and Therapeu tics 27: 72 (Jan 1980)

0158·2703/ 90/0209-00 15 $00.50/ 0 C ADIS Pless INPHARMA 9 Feb 1980 15