Identification of etretinate metabolites in human blood.

Five metabolites were isolated from the blood of psoriatic patients on chronic therapy with etretinate (Tegison). The two major metabolites were the all-trans acid (acitretin) and the 13-cis acid (isoacitretin), both of which had been previously identified as major metabolites of etretinate in human blood. The other three metabolites had not been previously reported in human blood. One metabolite corresponded to isoacitretin with a hydroxy group on an aromatic methyl group. The other two metabolites had acid side chains shortened by one carbon and a reduced 11, 12-double bond. One of the two metabolites retained the aromatic methoxy group, whereas the other was the phenolic analog.