Measurement of the bioavailability of aescin-containing extracts.

OBJECTIVE: In horse chestnut seed extracts (HCSE), the triterpene saponin mixture aescin is considered the active principle. The bioavailability and pharmacokinetics of different HCSE preparations have been studied under single and repeated applications using a radioimmunological method (RIA) developed to identify beta-aescin, one of the pharmacologically active fractions of the saponin mixture. In this paper, the available pharmacokinetic data are reviewed and the observed heterogenicity between comparable studies is discussed. DATA SOURCES: Pharmacokinetic data from 5 single- and 4 multiple-dose bioequivalence studies with HCSE-containing products, were measured by the same analytical laboratory using the same RIA. EVALUATION: In studies where procedures were identical the pharmacokinetic data of beta-aescin show high variations. Even under steady-state conditions a considerable variability for the same HCSE product is obtained. CONCLUSION: Formal reasons like study design and medications can be ruled out as a source of pharmacokinetic variation. In extracts of herbal drugs like HCS, the relative concentration of the individual saponin fractions can considerably differ from batch to batch. For immunological methods, identification of such antigens with intermolecular variability, e.g., the structural aescin analogs, is of unknown validity. Therefore the shape of the concentration-time curve would only show an approximation of the time course but not for the absolute concentrations. A specific validation procedure for the RIA must be developed, otherwise a LC-MS/MS-method of sufficient sensitivity should be elaborated.