Metabolism and pharmacokinetics of anthranoids

Anthranoid derivatives are used all over the world as a treatment for constipation. These compounds are present in several drugs of plant origin, especially as O- or C-glycosides. Besides featuring different substituents, the aglycone might consist of an anthraquinone, an anthrone or a dianthrone. So far, detailed information concerning their metabolism and pharmacokinetic characteristics is available only in a few cases. The best characterized compounds are sennoside, a dianthrone O-glycoside present in senna leaves and senna pods, and its aglycone (rhein anthrone). After oral administration, sennoside is degraded only in the lower parts of the gastrointestinal tract, releasing its active metabolite rhein anthrone. Nowadays, this process is understood at the molecular level. A study with 14C-labelled rhein anthrone administered intracecally to rats, revealed that the compound is scarcely absorbed. Since on the contrary its anthraquinone equivalent is absorbed to a much larger extent, it is inferred that dianthrone- or anthrone-glycosides exhibit a lower systemic availability than anthraquinone O-glycosides.