hTerapeutics and Clinical Risk Management Open Access Full Text Article Dovepress open access to scientific and medical research L E T T E R Pain management with morphine: variation in analgesic response secondary to genetic polymorphisms Shailendra Kapoor Mechanicsville, Richmond, VA, USA Correspondence: Shailendra Kapoor 2300 E Cary St Richmond, VA 23223, USA Tel +1 804 2342345 Fax +1 804 3454561 Email shailendrakapoor@yahoo.com To the editor The recent article by Villesen et al in a recent issue of your journal was most interesting.1 Recent studies show that the potency of morphine in efficacious pain control may be influenced greatly by polymorphisms of certain genes. For instance, Klepstad et al have recently shown that cancer patients on opioid maintenance therapy who are homozygous for the variant G allele of the 118 A . G polymorphism of the mu opioid receptor (OPRM1) gene require higher doses of mor- phine for efficacious pain control in comparison with patients who are heterozygous.2 In fact, the morphine requirement is almost 93% less in AA genotypes in contrast with morphine requirements in cancer patients who carry the GG genotype of the OPRM1 gene.3 Similar pain modulation variation is seen with polymorphisms of the OPRM1 gene and perioperative fentanyl administration.4 Furthermore, more profound CNS depressant side effects after morphine administration are noticed in cancer patients with certain polymorphisms of the multidrug resistance-1 gene.5 Similarly, the potency of morphine in pain management in cancer patients is influ- enced and varies greatly with polymorphisms of the catechol-O-methyl transferase gene.6 For instance, individuals with the Met/Met genotype of the catechol-O-methyl transferase gene require 63% less morphine in comparison with those who have the Val/Val genotype of the catechol-O-methyl transferase gene.3 More profound central nervous system side effects are seen following morphine administration in cancer patients with single nucleotide polymorphisms in intron 1 of the catechol-O-methyl transferase gene.5 The above examples clearly illustrate the variation in adequate pain control with morphine secondary to genetic mutations. Further research is needed to identify other similar gene polymorphisms that may affect opioid requirements in patients being managed with other nonmorphine narcotics. References 1. Villesen HH, Banning AM, Petersen RH, et al. Pharmacokinetics of morphine and oxycodone following intravenous administration in elderly patients. Ther Clin Risk Manag. 2007;3:961–967. 2. Klepstad P, Rakvag TT, Kaasa S, et al. The 118 A . G polymorphism in the human mu opioid recep- tor gene may increase morphine requirements in patients with pain caused by malignant disease. Acta Anaesthesiol Scand. 2004;48:1232–1239. 3. Reyes-Gibby CC, Shete S, Rakvag T, et al. Exploring joint effects of genes and the clinical efficacy of morphine for cancer pain: OPRM1 and COMT gene. Pain. 2007;130:25–30. submit your manuscript | www.dovepress.com Dovepress http://dx.doi.org/10.2147/TCRM.S32184 Therapeutics and Clinical Risk Management 2012:8 243–244 © 2012 Kapoor, publisher and licensee Dove Medical Press Ltd. This is an Open Access article which permits unrestricted noncommercial use, provided the original work is properly cited. 243