Radioimmunoassay of flunisolide in human plasma.

A simple radioimmunoassay was developed for the measurement of flunisolide in human plasma or serum. Plasma extraction was not required. Antiserums were produced in rabbits by immunization against the flunisolide 21-hemisuccinate-bovine serum albumin conjugate. Cross-reactivities were determined for cortisol and a major metabolite of flunisolide and were 0.02 and 0.06%, respectively. Assay sensitivity is in the 100--200-pg/ml range. Accuracy studies gave regression lines of y = 1.06x, r = 1.00, for a 0.1-ml plasma aliquot and y = 0.99x, r = 0.99, for a 0.2-ml plasma aliquot. The accuracy of the method was estimated to be at least +/- 15%. The method was used to determine plasma concentration-time profiles in human subjects after the administration of a 1.0-mg iv dose.