The use of 13C-nmr spectroscopy for the detection and identification of metabolites of carbon-13 labelled amitriptyline

Abstract

Abstract The antidepressant drug amitriptyline and two of its metabolites, nortriptyline and desmethylnortriptyline, each containing two 13C atoms, have been used to determine the sensitivity and selectivity of 13C-nmr spectroscopy for the detection of unchanged amitriptyline and N-desmethyl metabolites in the urine of animals dosed orally with the labelled drug. The resonance signals from the 13C atoms detected in the 13C-nmr spectrum of the entire extract from a control 12 h rat urine sample to which 1 mg of each labelled compound had been added were easily detected, using an instrument accumulation time of 1 h. The 13C-nmr spectrum of an extract of hydrolysed urine from a dog that had received an oral dose of [13Q]amitriptyline (30 mg) exhibited signals that could be assigned to metabolites resulting from N-dealkylation and N-oxidation, as well as those bearing the intact amitriptyline side-chain. These assignments were confirmed by analysis of the same extract by g.c.-ms and h.p.l.c.