Patients from around the world vary widely in their response to drugs

Patients from around the world vary widely in their response to drugs. It is estimated that genetic factors can account for 20 to 95 percent of patient variability. Polymorphisms may influence a drug’s action by changing its pharmacokinetics or its pharmacodynamics.
Pharmacokinetics, the study of the rate and extent of drug absorption, distribution, metabolism, and excretion (ADME), determine the fate of a drug in the body. A combination of metabolism and excretion facilitates drug elimination from the body, so these polymorphisms can effect drug transport. Genetic polymorphisms have been identified for many drug-metabolizing enzymes, including the cytochrome P450 (CYP450) enzymes, and have a ability to decrease the efficacy of these enzymes. This gives rise to unique population phenotypes of people who have metabolism capabilities ranging from extremely poor to extremely fast.
Pharmacodynamics, the study of the pharmacologic effect between the drug and the body. The relationship between the concentration of the drug and the observed pharmacologic response depends on the drug’s mechanism of action. Polymorphisms could alter the pharmacologic response to a drug through a direct effect like altering binding to a specific receptor or drug target, or an indirect effect like inhibiting an enzyme in a protein synthesis pathway.