Antimicrobial Effects

Although pharmacologic research has focused primarily on arbutin, the pharmacology of the whole plant is different from that of arbutin alone. The crude plant extracts are much more effective medicinally than the isolated constituent arbutin.⁵ This fact appears to be related to the activity of gallic acid, which prevents the splitting of arbutin by such enzymes as β-glucosidase contained in gut bacteria.² Arbutin undergoes hydrolysis in the stomach or intestinal tract to produce hydroquinone, its aglycone, which has urinary antiseptic properties.⁶ The hydrolysis of arbutin is responsible for much of the therapeutic effect of uva ursi.^1,6 By preventing the splitting of arbutin, the flavonoid components allow more arbutin to be hydrolyzed and absorbed than when arbutin is administered as an isolated component. Approximately 65% of an arbutin dosage is excreted in the urine as hydroquinone glucuronide or sulfate.^7,8

Arbutin alone has been reported to be an effective urinary antibiotic, but only if taken in large doses and if the urine is alkaline (once again documenting the value of whole-plant medicines).¹ It is reported to be active against Candida albicans and Staphylococcus aureus and especially against Escherichia coli.^5,9 Uva ursi also has diuretic properties.¹

Antiinflammatory Effects

Some early animal research is now showing that arbutin, and possibly other constituents of uva ursi, potentiate the activity of commonly prescribed antiinflammatory drugs. One study found that an aqueous extract increased the inhibitory activity of dexamethasone in allergic and inflammatory models without increasing any of the side effects.¹⁰ Similar results have been demonstrated with isolated arbutin combined with indomethacin.¹¹