Population pharmacokinetic analysis of ephedrine in Kampo prescriptions: a study in healthy volunteers and clinical use of the pharmacokinetic results.

We conducted a population pharmacokinetic analysis of ephedrine, the main effective constituent of the two Kampo prescriptions, Sho-seiryu-to (Xiao-Qing-Long-Tang, Formula divinitatis caeruleae minor) and Kakkon-to (Ge-Gen-Tang, Formula puerariae), which are routinely used in the treatment of allergic rhinitis. Major pharmacokinetic differences were found in AUC(0-infinity), Cmax and the averages of the distribution volume between the two prescriptions. Using the pharmacokinetic results, we also conducted a simulation-based study comparing the pharmacokinetic profiles of ephedrine for the usual dosage regimen, a constant dose D three times a day before meals, and two alternative dosage regimens which are often used when patients' symptoms are not improved in the morning using the usual dosage regimen. The results suggested that one of the two alternative dosage regimens, two times D before breakfast and D in the afternoon, was the most effective from the pharmacokinetic viewpoint. This result was in accordance with our clinical experience.