A Method for Estimating Theophylline Pharmacokinetic Parameters and Its Predictability for the Serum Concentration

To estimate pharmacokinetic parameters for individualized digoxin therapy, a method which is available to clinical practice was studied in 2 healthy volunteers and 4 patients with heart disease.At the beginning of a once-daily regimen, the prescribed dose was administered and 9 blood samples were drawn in 48 hours without receiving the dose on Day 2, if possible. On Day 3, a routine digoxin therapy was started and to estimate parameters more accurately, several additional blood samples were drawn just before the next dose of digoxin for measuring the minimum digoxin concentrations (SGC) and 2 hours after the digoxin ingestion for maximum SGC.The ability to predict SGC of this method based on repetitive dosing data was evaluated by comparing observed and predicted SGC. There was statistically significant correlation between observed and predicted SGC, where the prediction error was 11.9±9.4 (mean% S. D., n= 20). The method based on repetitive dosing data can be used in clinical practice, because fairly accurate parameters can be obtained by this method without interrupting a routine digoxin therapy.