A sensitive enzyme immunoassay (EIA) for quantitation of the topical anti-inflammatory agent SCH 40120 in unextracted human plasma.

SCH 40120 is a potent acute anti-inflammatory agent under development for topical treatment of dermal inflammatory and allergic disorders such as atopic dermatitis, contact dermatitis and psoriasis. In order to support percutaneous absorption studies, a competitive enzyme immunoassay (EIA) was developed to determine SCH 40120 in unextracted plasma samples. SCH 38280, a carboxylated analogue of SCH 40120, was used as the hapten and conjugated with bovine thyroglobulin (Thy). The hapten-Thy conjugate was used as the immunogen to immunize rabbits for antibody production. The hapten was also coupled to horseradish peroxidase (HRP) to form SCH 38280-HRP, which was used as the tracer. The EIA can detect SCH 40120 concentrations as low as 50 pg ml-1 of plasma, and can reliably quantitate SCH 40120 in plasma samples from 100 pg ml-1 to 10 ng ml-1 with good linearity, accuracy and precision. A variety of structurally related compounds and potential metabolites did not significantly cross-react with the antibodies, except for a few analogues. The availability of this sensitive assay makes it possible to evaluate the pharmacokinetics of SCH 40120 in man.