Radioimmunoassay of amitriptyline and nortriptyline in body fluids

A radioimmunoassay for the measurement of amitriptyline and nortriptyline in serum, saliva, and urine is described. The sensitivity of the assay is such that 0.5 ng/ml of drug can be measured, although the assay does not distinguish between amitriptyline and nortriptyline. Other tricyclic compounds cross-react with the antiserum to varying degrees, but the metabolites of amitriptyline did not significantly cross-react. Total tricyclic compounds were detected in serum and saliva after single oral doses of amitriptyline, although the absorption was slow.