J Clin Pharmacol. 2002 Aug; 42(8): 920-7.

Urinary excretion and metabolism of arbutin after oral administration of Arctostaphylos uvae ursi extract as film-coated tablets and aqueous solution in healthy humans.

Schindler G, Patzak U, Brinkhaus B, von Niecieck A, Wittig J, Krähmer N, GlÃƒÂ¶ckl I, Veit M.

Friedrich-Alexander University, Erlangen-Nuremberg, Department of Medicine I, Erlangen, Germany.

Bearberry leaves and preparations made from them are traditionally used for urinary tract infections. The urinary excretion of arbutin metabolites was examined in a randomized crossover design in 16 healthy volunteers after the application of a single oral dose of bearberry leaves dry extract (BLDE). There were two groups of application using either film-coated tablets (FCT) or aqueous solution (AS). The urine sample analysis was performed by a validated HPLC coolarray method (hydroquinone) and a validated capillary electrophoresis method (hydroquinone-glucuronide, hydroquinone-sulfate). The total amounts of hydroquinone equivalents excreted in the urine from BLDE were similar in both groups. With FCT, 64.8% of the arbutin dose administered was excreted; with AS, 66.7% was excreted (p = 0.61). The maximum mean urinary concentration of hydroquinone equivalents was a little higher and peaked earlier in the AS group versus the FCT group, although this did not reach statistical significance (Cur max = 1.6893 micromol/ml vs. 1.1250 micromol/ml, p = 0.13; tmax (t midpoint) = 3.60 h vs. 4.40 h, p = 0.38). The relative bioavailability of FCT compared to AS was 103.3% for total hydroquinone equivalents. There was substantial intersubject variability. No significant differences between the two groups were found in the metabolite patterns detected (hydroquinone, hydroquinone-glucuronide, and hydroquinone-sulfate).