Opioid genetics in the context of opioid switching.
OBJECTIVE
On a population level, there is no difference in terms of efficacy or side-effects between any of the strong opioids. On an individual level, however, there is marked variation in response to opioids. This review presents some of the recent advances in opioid pharmacogenetic studies.


RESULTS
A growing number of genes have been studied in a number of different patient populations. Most data have come from candidate-gene studies. There have been two genome-wide association studies in pain and opioid response. The clinical and genetic complexity of response to opioids has limited the clinical applicability of the genetic results. Currently, interindividual variation in opioid response is managed clinically through a process known as opioid switching. The evidence supporting the efficacy of opioid switching is poor, mainly because randomized controlled trials in this area are lacking.


CONCLUSIONS
Adequately powered studies to allow identification of genetic variants with small effect size and exploration of gene-gene interaction are needed. Integration of genetic analysis in clinical studies with carefully defined outcome measures will increase the likelihood of identifying clinical and genetic factors which can be used to predict opioid response.
Royal Marsden Hospital, London, UK. j.droney@nhs.net
Joanne
J
Droney
Julia
J
Riley
Joy
J
Ross
D000701:Analgesics, Opioid / Q000494:pharmacology / Q000627:therapeutic use*; D004844:Epistaxis; D059647:Gene-Environment Interaction; D020022:Genetic Predisposition to Disease; D014644:Genetic Variation / Q000235:genetics; D055106:Genome-Wide Association Study; D006801:Humans; D009369:Neoplasms / Q000188:drug therapy / Q000235:genetics*; D010146:Pain / Q000188:drug therapy* / Q000235:genetics; D010597:Pharmacogenetics; D010641:Phenotype
D000701:Analgesics, Opioid