Decreased Analgesic Effect of Tramadol in Japanese Patients with CYP2D6 Intermediate Metabolizers after Orthopedic Surgery

Tramadol is metabolized by CYP2D6 to an active metabolite, which in turn acts as an analgesic. This study aimed to investigate the impact of CYP2D6 genotype on the analgesic effect of tramadol in clinical practice. A retrospective cohort study was performed in patients treated with tramadol for postoperative pain after arthroscopic surgery for rotator cuff injury during April 2017–March 2019. The impact of CYP2D6 genotypes on the analgesic effects was assessed by the numeric rating scale (NRS) pain scoring and analyzed by the Mann–Whitney U test. Stepwise multiple linear regression analysis was performed to identify predictive factors for the area under the time-NRS curve (NRS-AUC), which was calculated using the linear trapezoidal method. Among the 85 enrolled Japanese patients, the number of phenotypes with CYP2D6 normal metabolizer (NM) and intermediate metabolizer (IM) was n = 69 (81.1%) and n = 16 (18.9%), respectively. The NRS and NRS-AUC in the IM group were significantly higher than those in the NM group until Day 7 (p