Catecholamine polymorphism influences opioid use

By Lucy Piper, Senior medwireNews Reporter

The catechol-O-methyltransferase (COMT) rs4680 single nucleotide polymorphism could affect postoperative opioid consumption, study findings show.

Among 152 patients undergoing nephrectomy, those homozygous for the high enzymatic activity genetic Val/Val variant consumed 36% more opioids in the first 24 hours following nephrectomy than patients homozygous for the low enzymatic activity Met/Met genotype.

This was despite both groups having similar pain scores and requiring the same amount of emesis medication.

“Clinically, this suggests that patients expressing the Met/Met genotype and having higher opioid receptors in critical regions might require less opioid to produce adequate pain control, while those possessing the genotype Val/Val may require relatively more opioid”, the researchers, led by Keith Candiotti, from University of Miami School of Medicine in Florida, USA, explain.

The patients were divided into three groups according to rs4680 genotype: 61 had the Met/Met genotype, 60 had the Val/Met genotype and 31 had the Val/Val genotype.

Average opioid consumption 24 hours after surgery was 31.9 mg for patients with the Met/Met genotype, 37.5 mg for those with the Val/Met genotype and 49.4 mg for those with the Val/Val genotype.

The higher opioid consumption in Val/Val patients versus Met/Met patients was significant for the entire 48 hours after surgery, while the greater consumption in Val/Val patients versus Val/Met patients was only significant for the first 6 hours.

Smoking also had a significant effect on opioid consumption, with smokers needing more of this type of pain relief than nonsmokers. However, smoking did not lessen the effect of rs4680 genotype on opioid consumption, nor did age, gender, body mass index or type of surgery.

The researchers also looked at the effect of COMT rs4818 genotype on opioid consumption, but found that patients homozygous for the gene variant (GG) only had a significantly greater opioid consumption than patients homozygous for the CC genotype during the first 6 hours after surgery.

This polymorphism, unlike the COMT rs4680 polymorphism, was significantly associated with variations in emesis medication, with greater use in patients with the CC genotype versus the CG and GG genotypes.

Candiotti and team conclude in Anesthesia & Analgesia that, although their findings suggest a role for genetic analysis in predicting the pain phenotype, “practical use is likely years away.”

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