An ELISA for the measurement of VP16 (etoposide) in unextracted plasma

An ELISA for the anti-cancer drug VP16 in unextracted plasma has been developed using VP16-thyroglobulin-coated microtitre plates, a sheep anti-VP16 serum, and a donkey anti-sheep HRPO-labelled second antibody. The sensitivity of the assay was 0.5 ng/ml, providing a detection limit of 0.1 microgram VP16/ml plasma. Plasma interference effects were negligible and therefore the standard curve could be set up in assay buffer. A good correlation was obtained between the ELISA and established HPLC and RIA methods. No evidence was found of significant levels of cross-reacting metabolites in plasma samples obtained from patients receiving VP16 therapy. The antiserum did not cross-react with the epiaglycone of VP16.