A sensitive radioimmunoassay, incorporating solid-phase extraction, for fluticasone 17-propionate in plasma.

Antibodies were produced in rabbits immunized with fluticasone 17-propionate (FP) conjugated to bovine thyroglobulin via its 3-carboxymethoxime with isobutylchloroformate. The antibodies were used to develop a sensitive and specific radioimmunoassay (RIA) for FP in human plasma. The limit of quantitation of the RIA is 50 pg per assay tube. This translates to 50 pg ml-1 plasma when a solid-phase extraction preceded the RIA. The interassay and intraassay relative standard deviations were < 15% in the centre of the assay concentration range rising to < 25% at the lower and upper limits (50 and 250 pg ml-1). No appreciable binding was seen between the antibodies and the metabolite of FP that has been identified in man. The RIA was used to study the time course of plasma concentrations in man following inhalation of FP.