Determination of nomifensine by a sensitive radioimmunoassay.

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Abstract
1. A radioimmunoassay (RIA) has been developed for determination of both nomifensine and total nomifensine (nomifensine + conjugated nomifensine) in serum, plasma, and urine. 2. Antibodies were prepared in rabbits by immunization with N‐(8‐Nomifensine) succinamic acid‐ bovine serum albumin. 3H‐labelled drug was used as tracer. Separation of free from antibody‐bound nomifensine was carried out using dextran‐ coated charcoal. For determination of total nomifensine, the acid‐ labile conjugate was split by acidification. 3. The limit of detection for nomifensine is 300 pg/ml plasma and the cross‐reactivity of the metabolites is less that 1%. The influence of conjugated nomifensine on the results of nomifensine can be corrected. 4. Pharmacokinetics of nomifensine were determined in healthy volunteers after oral administration of 100 mg 14C‐labelled drug. Peak levels of 14C radioactivity (2,150 ng/ml), total nomifensine (1,252 ng/ml) and nomifensine (53 ng/ml) appeared within 1.5‐2 h; the half‐life of elimination from plasma was 1.5‐2 hours. The advantages of this routine method are high sensitivity, the requirement of small amounts of plasma, and simple handling.