Fig. 3From: Validated determination method of tramadol and its desmethylates in human plasma using an isocratic LC-MS/MS and its clinical application to patients with cancer pain or non-cancer painPlasma concentrations of tramadol, O-desmethylate, N-desmethylate, and N,O-didesmethylate obtained from patients with cancer pain (a) or non-cancer pain (b) just before treatment of oral tramadol on day 4 or later. (1) Tramadol, (2) O-desmethylate, (3) N-desmethylate, and (4) N,O-didesmethylateBack to article page