Pharmacogenetics and cutaneous drug reactions

Variations in therapeutic efficacy and ADRs in the population are known for many drugs. When individuals are adversely affected by their therapy, it suggests the possibility of a pharmacogenic predisposition. Genetic variants and polymorphism affect the metabolism and sites of action of many agents, and the expression of genetic variations is modified by both host and external factors. Many of these metabolic defects are well-described and are important to the clinician who is evaluating an adverse reaction to either old or new drugs. The systematic evaluation of drug effects demands attention to subgroup and individual variation in metabolism of the drug and susceptibility to its effects. Practically every class of drug shows individual variation in responses and once the variation has been recognized and categorized, there are implications for other drugs (some seemingly unrelated) and for family members.