Relative Bioavailability of Quinidine Gluconate and Quinidine Sulfate in Healthy Volunteers

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Abstract
A comparison of the bioavailability of quinidine sulfate to quinidine gluconate [antiarrhythmic drugs] tablets in a single-dose randomized crossover design with 20 healthy volunteers shows that the sulfate salt is more rapidly absorbed and provides significantly greater peak concentrations 1 h after administration than the peak levels achieved with the gluconate salt at approximately 5 h after administration. When adjusted for the actual amount of quinidine contained in each tablet, there was no significant difference in the amount of quinidine bioavailable. Since quinidine gluconate absorption is significantly slower than quinidine sulfate, a combination of the 2 dosage forms may be utilized in providing the loading dose. Based on the computer modeling and the clinical data accumulated over the past 4 yr, quinidine gluconate in the dosage form used in the study provides more constant blood levels with smaller differences between the Cpmax [maximum plasma clearance] and Cpmin [minimum plasma clearance] than the sulfate when administered every 6 or 8 h. Further controlled clinical studies are needed to confirm the observations.