CYP2D6 Basic Genotyping of Patients with Chronic Pain Receiving Tramadol or Codeine. A Study in a Greek Cohort

To assess CYP2D6 genotype prevalence in chronic pain patients treated with tramadol or codeine.

Prospective cohort study.

General hospital, pain management unit.

Patients with chronic pain, treated with codeine or tramadol.

Patients' pain was assessed at baseline (numeric rating scale [NRS]; 0-10). Prescription of codeine or tramadol was selected randomly. The assessment of patients' response to the drug in terms of pain relief and adverse effects was performed after 24 hours. Reduction of pain intensity of >50% or an NRS <4 was considered a positive response. Patients' blood samples were collected during the first visit. Genotyping for the common variants CYP2D6 *2, *3, *4, *5, *6, *9, *10, *14, and *17 was performed, and alleles not carrying any polymorphic allele were classified as CYP2D6*1 (wild-type [wt]).

Seventy-six consecutive patients were studied (20 males, 56 females), aged 21-85 years. Thirty-four received tramadol and 42 codeine. The main genotypes of CYP2D6 identified were the wt/wt (35.5%), the *4/wt (17.1%), and the *6/wt (10.5%). Adverse effects were common, especially in carriers of *9/*9, *5/*5, *5/*4, and *10/*10, as well as in variants including the 4 allele (*4/*1 [38.4%] and *4/*4 [42.8%]).

Genotyping can facilitate personalized pain management with opioids, as specific alleles are related to decreased efficacy and adverse effects.