We have discussed how an enzyme important to the metabolic pathway of a certain drug can be deficient or defective due to hereditary factors (polymorphisms) and how these deficiencies can cause the drug to accumulate in the body (as seen in “poor metabolizers”) or have reduced efficacy (as seen in “ultrarapid metabolizers”).
Genetics can also indirectly influence the biotransformation of a drug. Genetic variation in the genes that control the synthesis of drug receptor sites can affect the concentration of free drug not bound to receptor in the blood stream that is available for metabolic processes. The bioavailability of the drug can also be affected by variation in genes that control the synthesis of proteins available for protein binding.