Pharmacogenomics and variation in drug therapy

Pharmacogenomics is a scientific and clinical discipline that examines the genetic basis for individual variations in response to therapeutics. Polymorphism of genes encoding drug metabolizing enzymes, protein transporters and receptors would affect drug metabolism, absorption, distribution and elimination. Individuals may be classified as ultra-rapid, wild-type (normal), intermediate and poor metabolizers for having multiple copies of the gene, no mutation in both chromosomes, one mutation in one chromosome and mutations in both chromosomes. Correspondingly, the dosage should be adjusted to achieve the same steady state concentrations. Just as important, drug-drug interactions might also contribute to variations of drug concentration, resulting in possible drug toxicity or sub-therapeutic outcome. The applications of pharmacogenomics for understanding the variations in drug toxicity and drug therapy would be illustrated in forensic toxicology, psychiatry, and pain management.