Pharmacokinetics and biotransformation studies of terfenadine in man.

Comparison of plasma level data obtained from a dose-response study to that of a 14C material balance study indicates that 99.48% of the alpha-[4-(1,1-dimethylethyl)phenyl] 4-(hydroxydiphenylmethyl)-1-piperidinebutanol (terfenadine, RMI 9918, Triludan, Teldane, resp.) related material absorbed undergoes biotransformation. From the balance study it has been determined that fecal excretion accounts for ca. 60% of the dose administered. Thin-layer chromatographic analysis of urine and feces revealed the presence of two major metabolic products. These compounds have been isolated and their structures determined by GC-MS. One of the metabolic products, a carboxylic acid analog of terfenadine has been shown to have antihistaminic activity and may play a role in the activity of the parent drug in vivo.