| A person’s genetic makeup not only determines his or her predisposition to developing certain conditions; as researchers are discovering, it also can impact how an individual’s body responds to a specific drug. Whether a drug is metabolized slowly or quickly, or if the medication has the desired effect or does not work well, may be due to certain genetic variations. |
Pharmacogenetics, the study of how genetics influence a person’s response to a drug, began in the 1950s. Then, the emphasis was on how certain ethnic groups metabolized drugs; today, with advancements such as gene and protein sequencing, the focus is on the individual. With the new technology and a sample of cheek cells or blood, a person’s genotype, a specific genetic code, can be produced.
A genotype provides all types of information, including whether there are gene variations that affect the way the body reacts to certain drugs. Of particular interest is the Cytochrome P450, a group of enzymes that process chemicals in the body. The genetic variations of P450 can affect how a drug is metabolized and how long it remains in the body. This information is important, because if the drug is metabolized too quickly, the patient might not receive the medicine’s full effect. Slowly metabolized drugs present a different problem: otherwise perfectly acceptable doses of a medicine could build up in a person’s body to the point of toxicity.
P450 is involved in the body’s processing of many of the most widely prescribed medications, including antidepressants, blood thinners, and beta blockers. By testing the blood for P450 variations, a doctor can make any necessary adjustments in dosage or prescribe a different medication altogether. For example, a person who has the slow-metabolizing form of Cytochrome P450 2C9 enzyme, which metabolizes coumadin, may need a lower dose than other people without the genetic variation.
Persons who have had adverse reactions or less than satisfactory responses to medications processed by Cytochrome P450 may be candidates for testing.
A More Individualized Treatment Plan
Today’s advances in pharmacogenetics are but the tip of the iceberg. The more that is known about the interrelationship between human genes and medication, the more relevant information physicians will have when prescribing drugs for specific individuals. For example, wholesale withdrawal from the market of drugs, such as Vioxx, that are helpful to a large number of people, but dangerous to others, could be avoided if genetic variations leading to harm could have been identified ahead of time.