The metabolism of anthranoid laxatives

The anthranoid compounds, which chemically can be described as dihydroxy-anthraquinones, -dianthrones and -anthrones, possess a laxative effect. As these substances are the constituents of some plants and their extracts, they are often referred to as vegetable laxatives. If present in the glycoside form, these compounds represent unique targeting molecules; after oral administration they are carried, unabsorbed, to the large intestine, where the active aglycon is released by bacterial hydrolysis of the sugar. The intestinal bacterial flora also accounts for the reduction of anthraquinone aglycons to the corresponding anthrones. After absorption, the anthranoids are transformed mainly to their corresponding glucuronide and sulfate derivatives, which appear in urine and bile. Experiments with radiochemical anthranoids showed a significant clearance of tissue-bound activity of all organs, except the kidneys, which exhibited a pronounced retention of anthranoid equivalents. It is argued that therapy with anthrone C-glycosides (present, for example, in cascara) or dianthrone O-glycosides (present for example, in senna) is preferable therapy with anthraquinones, as the anthranoid moiety of the former seems to be substantially less readily absorbed from the gastrointestinal tract.