title: Comparison of bioavailability in man of tamoxifen after oral and rectal administration.
abstract: The bioavailability of tamoxifen from 40 mg suppositories was tested in six male volunteers and compared with that of tamoxifen (Nolvadex) tablets. Plasma concentrations of tamoxifen and its major metabolites, 4-hydroxytamoxifen and N-desmethyltamoxifen, were measured by extraction from plasma obtained at different times after administration, separated by HPLC, converted on-line to fluorescent phenanthrene derivatives and quantified with a fluorescence detector. The mean relative bioavailability from the suppositories was 28%; the addition of a surfactive agent diminished the bioavailability to 13%. Simulation of repeated administration of 40 mg suppositories suggests a mean steady state plasma concentration for tamoxifen of approximately 70 ng ml-1, i.e. 30% of the steady state value after simulated oral administration. Rectal administration of tamoxifen leads to a lower bioavailability than that by oral administration and therefore cannot be recommended when used in equivalent doses.
mesh_terms: D000284:Administration, Oral; D000285:Administration, Rectal; D000328:Adult; D001682:Biological Availability; D006801:Humans; D008297:Male; D012995:Solubility; D013056:Spectrophotometry, Ultraviolet; D013629:Tamoxifen / Q000008:administration & dosage / Q000378:metabolism*
chemical_list: D013629:Tamoxifen