Effects of type 1 and type 2 diabetes on the pharmacokinetics of tramadol enantiomers in patients with neuropathic pain phenotyped as cytochrome P450 2D6 extensive metabolizers

Abstract

The aim of this study was to evaluate the influence of poorly controlled type 1 (T1DM) and type 2 diabetes mellitus (T2DM) on the pharmacokinetics and metabolism of tramadol enantiomers in patients with neuropathic pain. Nondiabetic patients (control group, n = 12), patients with T1DM (n = 9) or T2DM (n = 9), all with neuropathic pain and phenotyped as cytochrome P450 2D6 extensive metabolizers, received a single oral dose of 100 mg racemic tramadol. Serial blood samples were collected over a 24-h period. Patients with T1DM showed reduced Cmax of both tramadol enantiomers. The plasma concentrations of the active (+)-M1 were significantly reduced in T1DM (area under the curve plasma concentration versus time (AUC∞ ): 313.1 ng·h/ml) when compared with nondiabetic patients (AUC∞ : 1246.6 ng·h/ml). The fraction unbound of (+)-M1 was increased in patients with T1DM. Patients with T1DM and T2DM showed reduced AUC and increased fraction unbound of (-)-M1. The reduced total plasma concentrations of the active (+)-M1 in patients with T1DM may not be of clinical relevance because they are counterbalanced by the increased fraction unbound.