Radioimmunoassay for tricyclic antidepressants

A sensitive radioimmunoassay for the determination of tricyclic antidepressants is described. The antibodies were produced in rabbits immunized with a conjugate of N-succinyl-nortriptyline and human serum albumin and they were shown to be specific for the tricyclic antidepressant group of drugs. The assay was tested for the determination of amitriptyline and nortriptyline concentrations in plasma or serum. Specificity was achieved by coupling a simple extraction procedure (based on selective extraction of amitriptyline and nortriptyline at different pH-values) to the assay. Using [3H]imipramine as the tracer the sensitivity of the assay is 3.8-18.0 nmol/l depending on whether the extraction procedure is used or not and it can be carried out with 50-200 microliter sample volumes. Because of its advantages (sensitivity, specificity, simplicity, small sample volumes, low cost) this procedure is suitable for drug monitoring both during controlled tricyclic therapy and pharmacokinetic studies.