Drug therapy is a common part of everyday life, from managing acute illnesses to treating chronic conditions. Nearly 49 percent of people in the United States used at least one prescription drug in the last 30 days, according to the Centers for Disease Control and Prevention (CDC). And that doesn’t count the over-the-counter medications that people also take.
Understanding how your body metabolizes medications may explain how a certain drug works for you, or whether you’ll receive any benefit from it at all. In some cases, the typical dose of a drug may be too much or too little for your specific genetic makeup.
The CDC estimates that each year, some 1.3 million people—or one in 250 Americans—go to the emergency department because of a bad reaction to a medication. More than a quarter of them will need to be hospitalized for additional treatment.
The drug classes most responsible for these adverse drug events are blood thinners, antibiotics, diabetes drugs, and opioid analgesics. In an era of opioid addiction and overdose, medication metabolism may be critical to understanding appropriate dosing of opioids and other medications.
What Your Body Does with Drugs
How your body chemically alters pharmaceuticals so that they can be more easily processed and excreted, is called medication metabolism.
Even though it occurs in many of your body’s tissues, your liver holds the main responsibility for drug metabolism. It contains enzymes that usually break down or inactivate drugs. In some cases, though, these enzymes actually convert the drug into a form that your body can use more effectively. Other proteins, known as p-glycoproteins, can affect the absorption or brain penetration of certain drugs—in particular, some opioids and antidepressants.
Drugs are metabolized by the body using one of several processes, but regardless of the process, the rate at which your body metabolizes medications can impact both the drug’s efficacy and toxicity. It’s one of the main reasons why you can experience success with a drug therapy, or get into trouble. For instance:
If your body metabolizes a drug too quickly, you may not get any benefit from the prescribed dose. Your dose may need to be increased to reach a therapeutic effect.
If your body metabolizes a drug too slowly, it stays active longer, and may be associated with side effects.
Because of this, your doctor may characterize you as being one of four metabolizer types, with respect to a specific enzyme.
- Poor metabolizers have significantly reduced or non-functional enzyme activity.
- Intermediate metabolizers have low or reduced enzyme activity.
- Extensive metabolizers have normal enzyme activity.
- Rapid or ultra-rapid metabolizers have high enzyme activity.
What Determines Your Drug Metabolism?
Several factors affect your body’s rate of metabolism.
- Genetic Factors. Of all the metabolic enzymes, the ones produced by the cytochrome P450 (CYP450) gene group are among the most important. They make up 70 to 80 percent of enzymes involved in drug metabolism. The CYP450 gene group contains thousands of genetic variants. You can have a genetic variant or mutation that can affect your body’s ability to metabolize certain drugs, such as psychiatric medications.
- Coexisting Disorders. Underlying health conditions can also influence your drug metabolic rate. Some concerning ones are chronic liver disorders, kidney dysfunction, or advanced heart failure.
- Drug and Food Interactions. CYP450 enzymes can be impacted by the foods you eat and other drugs you take. These can either increase or decrease CYP450’s ability to break down drugs. When they increase the enzyme’s metabolic function, the drug’s therapeutic effects may be decreased. When they decrease the enzyme’s metabolic function, the drug’s benefits may be compromised by intolerability.
- Your metabolic enzyme systems change throughout your lifetime. At birth, these systems are only partially developed. That’s why newborns have difficulty metabolizing certain drugs. It’s one of the reasons why pediatric doses are lower than adult doses, and why some medications aren’t safe for infants or children.
Starting in late middle-age, our risk of medication side effects increases, in part because decreased blood flow and liver volume reduce the CYP450 activity in the liver by 30 percent or more. Because of this, older people can have difficulty metabolizing drugs. Like infants and children, older adults often need smaller doses per pound of body weight, compared to young or middle-aged adults.
The goal for any drug treatment plan is being on the right medication, at the right dose. Knowing your medication metabolism is another piece of the puzzle that can help you optimize efficacy while reducing or eliminating side effects.
Genetic Testing for Medication Metabolism
Usually, we can’t tell ahead of time how we metabolize a drug: a doctor prescribes, you adhere, and either the treatment works or not—and, in some cases, you may suffer side effects. However, treatment doesn’t have to be trial and error-based.
For decades, people have been trained to know their blood type. And now, in the era of personalized medicine, it is important to know your Rx MetaTypeTM, which can be determined through genetic testing. This is because the FDA requires labeling on over 260 medications to include pharmacogenetic biomarker information, due to specific actionable gene-drug associations.
Genetic tests, such as Genomind Professional PGx Express, can help identify the pharmacokinetic genes, such as CYP450, that determines the effect that the body has on a drug via metabolism (basically, your Rx MetaTypeTM ) and, as a result, inform dosing decisions. Such tests can also provide information on pharmacodynamic genes, which play a role in determining a drug’s effect on the body, and can help inform drug selection.
Genetic testing can help your health care provider determine how you metabolize certain drugs and decide on the treatment that may be right for you.