Pharmacokinetics of salicin after oral administration of a standardised willow bark extract

Objective: To evaluate the pharmacokinetics of salicin and its major metabo lites in humans after oral administration of a chemically standardised will ow bark extract. Methods: Willow bark extract corresponding to 240 mg salicin (1360 mg, 838 mu mol) was ingested by ten healthy volunteers in two equal doses at times 0 h and 3 h. Over a period of 24 h, urine and serum levels of salicylic aci d and its metabolites, i.e. gentisic acid and salicyluric acid, were determ ined using reverse-phase high-performance liquid chromatography. Renal excr etion rate, elimination half-life and total bioavailability of salicylates were calculated. Results: Salicylic acid was the major metabolite of salicin detected in the serum (86% of total salicylates), besides salicyluric acid (10%) and genti sic acid (4%). Peak levels were reached within less than 2 h after oral adm inistration. Renal elimination occurred predominantly in the form of salicy luric acid. Peak serum levels of salicylic acid were on average 1.2 mg/l, a nd the observed area under the serum concentration-time curve (AUC) of sali cylic acid was equivalent to that expected from an intake of 87 mg acetylsa licylic acid. Conclusion: Willow bark extract in the current therapeutic dose leads to mu ch lower serum salicylate levels than observed after analgesic doses of syn thetic salicylates. The formation of salicylic acid alone is therefore unli kely to explain analgesic or anti-rheumatic effects of willow bark.