Radioimmunoassay of glipizide in human plasma

A simple, sensitive radioimmunoassay has been developed for the direct determination of glipizide in human plasma. Antisera raised in rabbits immunized with a glipizide analogue conjugated to bovine serum albumin were highly specific, the two main metabolites, 3, cis-hydroxycyclohexyl derivative and 4,trans-hydroxycyclohexyl derivative, having cross reactivities of 0.73% and 1.66%, respectively. The method can measure amounts as small as 1 ng/ml. The intra- and inter-assay coefficients of variation lay between 2.98-5.79% and 2.35-8.66%, respectively. The mean recovery of glipizide added to plasma was 99-105% over the range 1-500 ng/ml. The method was employed to determine plasma levels in six subjects after administration of a 5 mg tablet of glipizide. The results were in accordance with those found after administration of the same dose of radiolabelled glipizide to two other subjects.