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OHP-026 Relevance of OPRM1 gene polymorphisms on chronic opioid treatment for cancer pain
  1. D González-Callejas1,
  2. M Cañadas-Garre1,
  3. M Rodriguez-Goicoechea2,
  4. R Cepa-Nogue3,
  5. MA Calleja-Hernández1
  1. 1Hospital Universitario Virgen de Las Nieves, Pharmacy Service. Pharmacogenetics Unit, Granada, Spain
  2. 2Hospital Universitario Virgen de Las Nieves, Pharmacy Service, Granada, Spain
  3. 3Hospital Universitario Virgen de Las Nieves, Palliative Care Unit, Granada, Spain

Abstract

Background The mu-opioid receptor gene (OPRM1) plays a key role in pain perception, response to opioids and opioid addiction. Several gene polymorphisms on OPRM1 have been associated with higher opioid requirements, opioid addiction and/or less control of pain. Among them, 118AG and 17CT are the most studied, which are uncommon in Caucasian patients: 1.7% GG genotype for 118AG and 0.8% TT genotype for 17CT, according to HapMAP-CEU.

Purpose To investigate the effect of OPRM1 genotype on fentanyl doses and the analgesic effect of oxycodone in a patient treated with opioids for oncologic pain.

Case report. Clinical and pharmacological data were collected from hospital records. Pharmacological interactions were assessed using Medscape Reference database. Genotyping of 118AG/17CT in OPRM1 was performed by Polymerase Chain Reaction and Direct Sequencing.

Results Male patient, 48 years old, diagnosed with lung adenocarcinoma stage IV. Bone and soft tissue metastases in the shoulder joint were confirmed by Computerised Tomography (CT) and Positron Emission Tomography/CT (PET/CT).

The patient was treated with increasing doses of transdermal fentanyl, from May to September 2013, until reaching 150 mcg/72 h. Additional oral fentanyl 1600 mcg/day was prescribed since September 2013.

After this period, patient continued to be in severe pain in his right shoulder and hospitalisation was required for uncontrolled pain. The patient was treated with intravenous infusions of oxycodone, increasing the dose up to 600 mg/day.

The pain remained uncontrolled throughout the treatment, and intravenous oxycodone 40 mg/4 h was additionally required on demand.

No pharmacological interactions were identified for the drug administered.

The patient was found to have the polymorphisms GG for 118AG and CC for 17CT OPRM1.

Conclusions The patient was homozygous for 118G, which could explain the higher opioid dose requirements, since numerous studies have been associated this genotype with higher fentanyl consumption, compared to heterozygous or homozygous for 118A, and with a reduction of analgesic effect in opioid treatment with oxycodone.

No conflict of interest.

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