Pharmacogenomics for the forensic toxicologist

Pharmacogenomics is the study of the linkage between an individual's genotype and the disposition of drugs in the body. The first association between adverse drug reactions and inherited variations was recognized in the 1950s, and since then, pharmacogenomics has come a long way. The importance of pharmacogenomics is accentuated by the incidence of adverse drug reactions, which may account for hospital expenditures of up to 5.6 billion dollars annually. Interindividual variations in drug metabolism are often the result of genetic variants or genetic polymorphisms, and polymorphisms have been known to alter the relationship between dose and plasma drug concentration. Drug disposition can be affected by polymorphisms in drug metabolizing enzymes, drug transport proteins, and drug targets. The cytochrome P450 (CYP) enzymes are responsible for the metabolism of a large number of drugs. Polymorphisms of the CYP enzymes have been well documented, and CYP2D6 is the most polymorphic CYP enzyme. However, there is a relative dearth of research on the role of transport proteins and drug targets. This review attempts to provide a brief synopsis of the pharmacogenomics of some common drug-metabolizing enzymes, transport proteins, and targets. The examples of tramadol, methadone, and oxycodone are used to illustrate the potential role of pharmacogenomics in forensic toxicology. Pharmacogenomics may present a practicable hypothesis in cases of incongruence between dose and plasma drug concentration, and the possibility of genotype-mediated drug plasma levels needs to be considered.