Specific radioimmunoassay of amitriptyline and nortriptyline.

1 Antisera to nortriptyline were prepared by immunizing rabbits with N-succinylnortriptyline--bovine serum albumin conjugate. 2 A sensitive radioimmunoassay has been developed for the tricyclic antidepressants amitriptyline and nortriptyline. 3 amitriptyline and nortriptyline are separated from each other and from interfering metabolites before assay. 4 Using [3H]-imipramine and [3H]-succinylnortriptyline as tracers the radioimmunoassay can measure amitriptyline and nortriptyline levels down to 2--3 ng/ml using 0.05 ml plasma sample. 5 Agreement between the radioimmunoassay and a gas-chromatographic assay was excellent for both amitriptyline and nortriptyline.