Genetic Testing for Enzymes of Drug Metabolism: Does It Have Clinical Utility for Pain Medicine at the Present Time? A Structured Review

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Abstract
Study Design. This is a structured review of genomic (genetic) testing for enzymes of drug metabolism. Objectives. Recently, industry began offering genomic testing for enzymes of drug metabolism. As such, the objective of this review was to determine if genomic testing for enzymes of drug metabolism has any imminent clinical relevance for the practice of pain medicine. Methods. Relevant references relating to pharmacogenetics, pharmacogenomics, and the metabolizing of drugs used in pain medicine by cytochrome P-450 enzymes were located and reviewed in detail. The P-450 enzymes that metabolize each drug and whether that drug had been identified as being subject to a clinical consequence of a genetic polymorphism of the P-450 enzyme involved in its metabolism were placed into tabular form. Results of Data Synthesis. 1) For a large number of drugs, we do not yet know which cytochrome P-450 enzymes are involved in their metabolism; 2) For a large number of drugs, the consequences of a P-450 genetic polymorphism have yet to be determined; 3) Genetic polymorphism can lead to important potential clinical consequences for some opioids, anticonvulsants (phenytoin), benzodiazepines (diazepam), muscle relaxants (succinylcholine), antidepressants (imipramine, nortriptyline, venlafaxine), typical neuroleptics, alcohol, antihypertensives (propranolol, timolol), local anesthetics (procainamide), L-dopa, nicotine, and warfarin. Based on these results, factors for and against using genomic testing were reviewed. Conclusions/Recommendations. It was concluded that genomic testing for enzymes of drug metabolism has significant potential for improving the efficacy of drug treatment and reducing adverse drug reactions. Recommendations for when such testing would be useful are outlined.