A simplified radioimmunoassay of plasma nortriptyline in depressed patients compared with high-pressure liquid chromatography and gas-liquid chromatography.

Antiserum to nortriptyline was generated in male New Zealand rabbits innoculated with n-succinylnortriptyline-bovine serum albumin conjugates. The antiserum was used at a final dilution of 1:4000 and tritiated imipramine was used as the label antigen. An accurate, sensitive, and specific radioimmunoassay of depressed patients' plasma or serum nortriptyline is described. The accuracy was good with a recovery range of 90-100% with a mean of 94%. The method can be used to measure nortriptyline concentration in the range of 0.1 microgram/liter to 100 micrograms/liter without prior extraction and purification of plasma or serum. Results of this method correlate well with those obtained by high-pressure liquid chromatography (r = 0.979) and by gas-liquid chromatography (r = 0.98). The specificity of the antiserum was examined by studying the cross-reactivity of 20 different psychopharmacological compounds, including nortriptyline's metabolites.