• Andrea Fanelli, Chiara Palazzo, Eleonora Balzani, Alessandra Iuvaro, Susi Pelotti, and Rita Maria Melotti.
• Anesthesia and Pain Medicine Unit, Department of Emergency and Urgency, Policlinico S.Orsola-Malpighi Hospital, Bologna, Italy.
• Pain Med. 2020 May 1; 21 (5): 1010-1017.

BackgroundA proper antalgic treatment is based on the use of titrated drugs to provide adequate relief and a good tolerability profile. Therapies have a variable effectiveness among subjects depending on medical and genetic conditions. CYP2D6 variations determine a different clinical response to most analgesic drugs commonly used in daily clinical practice by influencing the drugs' pharmacokinetics. This study was a monocentric clinical trial exploring the CYP2D6 variants in 100 patients with a diagnosis of chronic pain.MethodsDNA was extracted to evaluate the genotype and to classify patients as normal-fast (gNMs-F), normal-slow (gNMs-S), ultrarapid (gUMs), intermediate (gIMs), and poor metabolizers (gPMs) using the Activity Score (AS). Information on therapies and general side effects experienced by patients was collected. Nongenetic co-factors were evaluated to examine the discrepancy between metabolic profile predicted from genotype (gPh) and metabolic profile (phenocopying).ResultsThe distribution of our data underlined the prevalence of the gNMs-F (67%), whereas gNMs-S were 24%, gIMs 6%, gPMs 3%, and no gUMs were found, resulting in 33% of patients with reduced metabolic activity. In the analyzed population sample, 86% and 56% of patients, respectively, took at least one or two drugs inhibiting in vitro activity of the CYP2D6 enzyme.ConclusionsOver one-third of the enrolled patients showed altered CYP2D6 enzymatic metabolic activity, with a risk of phenocopying potentially due to polypharmacology.Trial RegistrationClinicalTrials.gov ID: NCT03411759.© 2019 American Academy of Pain Medicine. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

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