Identification and Determination of Opipramol Metabolites in Plasma and Urine

Abstract

In six cases of suspected opipramol overdose, commercially available immunoassays for tricyclic antidepressants (TCA) EMIT tox serum Assay and ADxR serum TCA Assay indicated arbitrarily high or toxic TCA concentrations. However, opipramol concentrations determined by high-performance liquid chromatography (HPLC) analysis were in the high-normal or low-toxic range. This finding prompted us to study opipramol metabolism by mass spectral techniques and to determine the cross-reactivity of opipramol and its metabolites in immunoassays. Three previously unknown metabolites (I, II, V) included an oxidation product of the hydroxyethyl moiety to an acetic acid group at the piperazine side chain (1), a decarboxylation product of the latter metabolite (II), and opipramol-N-oxide (V). In addition, two previously reported metabolites were identified, which included a deshydroxyethyl metabolite (III) and dibenzazepine (IV). One of the major metabolites of opipramol is the acetic acid metabolite (I), which may exceed the opipramol plasma concentration immensely and contribute to an arbitrarily high concentration in commercially available immunoassays. The cross-reactivities of the metabolite (I) were determined to be 64 and 66% with EMIT and ADx, respectively.

Structural elucidation of N‐oxidized clemastine metabolites by liquid chromatography/tandem mass spectrometry and the use of Cunninghamella elegans to facilitate drug metabolite identification

“…The m/z 100 fragment that was observed in the M4 and M5 spectra was not observed in the spectra of M6 and M7. Oxidative metabolism normally results in decreased retention in reversed‐phase HPLC but N ‐oxidation is an exception,25–27 which was another indication that M6 and M7 were N ‐oxides since the retention times of these metabolites were longer than that of the parent drug. To further explore the possibility of N ‐oxidation, H/D exchange experiments and experiments with APCI were applied.…”

Bioavailability of Opipramol from a Film-coated Tablet, a Sugar-coated Tablet and an Aqueous Solution in Healthy Volunteers

“…One such metabolite is deshydroxyethyl opipramol itself that was still detectable in plasma after one week. Recently, a metabolite formed by oxidation of the hydroxethyl side chain to the respective carboxylic acid has been found in high concentrations in plasma of patients after multiple dosing of opipramol [7]. We could detect this acid metabolite neither in plasma nor in urine.…”

“…However, probably we lost this acid metabolite during our sample-treatment that included extraction of plasma and urine at high pH where acids are hardly extracted into organic solvents, and we used a differing chromatographic separation system. Therefore, we analysed merely diluted and not extracted urine samples with the same chromatographic separation system as described by these autors [7]. Again, we could not detect this acid metabolite, whereas opipramol, opipramol N-oxide and deshydroxyethyl opipramol were clearly detectable.…”

“…Hence, we conclude that the carboxylic acid metabolite may accumulate in patients' plasma after multiple dosing, but is not formed in appreciable amounts and excreted into the urine in healthy volunteers after a single opipramol dose. Therefore, its role as main metabolite [7] seems questionable at least in healthy volunteers.…”

“…Recently, additional metabolites have been separated in serum of patients by HPLC and identified by gas chromatography coupled with mass spectrometry (Fig. 1) [7]. Opipramol is eliminated from plasma with a terminal half-life of 6−11 h (Novartis, data on file; [8]).…”