Validated methods for direct determination of hydroquinone glucuronide and sulfate in human urine after oral intake of bearberry leaf extract by capillary zone electrophoresis

Bearberry leaf extracts are used in herbal medicinal products for the treatment of lower urinary tract infections. Two metabolites of the major phenolic constituent in the extract, arbutin (hydroquinone-1-O-β-d-glucoside), must be assumed to be precursors of the active disinfectant principle hydroquinone. In order to assay the renal elimination of these two metabolites, i.e., hydroquinone conjugates with glucuronic and sulfuric acid, two separate capillary electrophoresis methods have been developed. Both methods were validated according to the criteria for validation of pharmaceutical bioanalytical methods as drafted by the US Department of Health and Human Services, 1998. As there is little sample preparation necessary, both methods are very suitable for urine analysis with large sample numbers as frequently coming up in the course of pharmaceutical bioavailability, bioequivalence and pharmacokinetic studies.