Abstract

Context: Inadequate pain relief is commonly experienced by patients on pain medications for chronic diseases. Tramadol, an opioid analgesic is metabolized by CYP2D6 to active metabolite, responsible for analgesic activity. The presence of non-functional CYP2D6*4 allele may affect pain relief. Hence the aim of our study is to investigate the influence of CYP2D6*4 on the analgesic effect of tramadol in acute osteoarthritic knee pain
Methods and Material: Seventy six patients visiting the orthopaedicians of MGMCRI with acute osteoarthritic knee pain and 49 fulfilling the study criteria were included. Pain intensity was recorded using visual analogue scale (VAS) at baseline and after 5 days. 2mL blood was collected for genotyping. Patients received Tab.Tramadol 50mg BD for five days. Patients were categorized as responders if patients experience 50% or more pain relief from the baseline. Genomic DNA was extracted using Qiagen Kit. Genotyping was performed using TaqMan SNP Assay on Real Time system.  Chi Square test was used to study the association between metabolizer phenotype determined by CYP2D6*4 and pain relief.
Results: The frequency of Extensive metabolizers(EM), Intermediate Metabolizers(IM) and Poor Metabolizers(PM) were 90.6%, 5.3% and 4% respectively. The allele was in Hardy Weinberg Equilibrium (p=0.1062). There was a statistically significant association between the metabolizer phenotype and pain relief (p=0.0349). There were significantly more number of responders with EM phenotype.
Conclusion: The genotype of CYP2D6*4 non-functional allele influences the analgesic effect of tramadol. However, studies on larger samples are required to extrapolate it.