Milk transfer of rhein in the rhesus monkey.

A HPLC method was developed to measure rhein, a laxatively active metabolite of sennosides A + B, in milk and plasma. Samples from 2 lactating rhesus monkeys were taken over 48 h after oral administration of sennosides (1 mg kg-1). Detectable rhein levels were found in plasma between 2 and 12 h and in milk between 4 and 12 h after administration, but rhein excretion in milk seems to be far below the dose necessary to elicit a laxative effect in the suckling offspring.