Rapid elimination of quinidine in pediatric patients

The oral absorption and elimination of quinidine in pediatric patients was studied. Single oral doses of quinidine sulfate were administered to 13 patients ranging in age from 4 to 22 years of age. Serum quinidine concentration reached a peak within 30 minutes to two hours after drug administration. The serum half-life of quinidine varied from 2.5 to 6.7 hours and was, on the average, shorter than the reported estimates for adult volunteers and cardiac patients (means ranging from 4.9 to 7.3 hours). Hence more frequent dosing or the use of slow-release preparations may be necessary in some pediatric patients in order to avoid excessive fluctuation in serum drug concentrations over a dosage interval. The oral dose clearance of quinidine (ie, oral dose divided by the area under the serum concentration time curve) varied over a threefold range, from 0.151 to 0.570 liter/hr/kg, and was found to correlate inversely with age (r = .80). In comparison with mean clearance estimates that have been reported for normal adult volunteers (0.293 +/- 0.078 liter/hr/kg), children less than 12 years of age (0.461 +/- 0.117 liter/hr/kg) were found to have significantly higher clearances, whereas no difference was observed between older children (0.287 +/- 0.101 liter/hr/kg) and adults. Inasmuch as the average steady-state serum drug concentration for a given daily maintenance dose is directly related to clearance rate, children less than 12 years of age may require a higher dosage of quinidine on a per kilogram of body weight basis. Proper selection of quinidine dosage, careful adjustment of dosage according to age, and regular monitoring of drug response and serum drug concentration are essential steps to a rational management of quinidine therapy in children.