Determination of Captopril in Human Blood by an Enzyme-linked Immunosorbent Assay

An immunoassay for the quantitation of the angiotensin‐converting enzyme inhibitor, captopril in human plasma is described. Antisera very specific for captopril were produced by immunization with captopril conjugated to bovine serum albumin or porcine thyroglobulin via the drug's thiol group. The antibodies were used to develop an enzyme‐linked immunosorbent assay (ELISA) with a detection limit of 0.3 ng mL−1 and intra‐ and inter‐assay coefficients of variation of 7 and 12%, respectively. Apart from stabilizing captopril by the addition of N‐ethyl maleimide, the assay was used to detect the drug in human plasma without further extraction or purification. Our immunoassay provides a very sensitive and rapid (four hours) alternative for the study of captopril pharmacokinetics.