Analysis of tramadol and O-desmethyltramadol in decomposed skeletal tissues following acute and repeated tramadol exposure by gas chromatography mass spectrometry

• Rats were exposed to tramadol under acute and repeated doses patterns prior to decomposition.
• Plasma and bone was analyzed for tramadol and O-desmethyltramadol by GC/MS.
• Plasma analyte levels differed significantly between exposure patterns.
• Bone analyte levels did not differ significantly between exposure patterns.
• Drug-metabolite concentration ratios were most discriminatory between exposure patterns in bone.

Decomposed bone and plasma samples of rats exposed to tramadol (TRAM) under different dosing patterns were analyzed. Wistar rats received TRAM as one acute dose (n = 4, 45 mg/kg, i.p.) or three doses (n = 4, 15 mg/kg, i.p.), 40 min apart. Perimortem heart blood was collected, rats were euthanized and placed outdoors to decompose to skeleton. Recovered bone was ground and subjected to methanolic extraction. Bone extracts and plasma samples underwent solid phase extraction and were analyzed using gas chromatography–mass spectrometry. Levels of TRAM and the primary metabolite O-desmethyltramadol (ODMT) were expressed as mass normalized response ratios (RR/m).Levels (RR/m) for TRAM and ODMT did not differ significantly between exposure types in any of the bone types examined or for the pooled bone comparisons (Mann–Whitney, p > 0.05). However, ratios of analyte levels (RRTRAM/RRODMT) differed significantly between exposure patterns for tibial and skull bone as well as for pooled bone comparisons (Mann–Whitney, p < 0.05). Levels of TRAM and ODMT, as well as ratios of analyte levels (RRTRAM/RRODMT), differed significantly in plasma between exposure patterns. Bone TRAM and ODMT levels were poorly correlated to corresponding plasma levels (TRAM: r = 0.33-0.57; ODMT: r = −0.35–0.23).