A Guide to Pharmacogenomics Testing

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It is estimated each year in the United States that 3% to 7% of all hospital admissions are due to adverse reactions to drugs.1 Approximately 10% to 20% of adverse drug reactions happen during hospitalization, and about 10% to 20% of these adverse reactions are severe.1 Some of these reactions are fatal. These numbers demonstrate that harmful reactions to drugs are a serious health problem in the United States. One way J. Flowers Health Institute reduces the chances of an adverse response to a drug is through the use of pharmacogenomics as part of a comprehensive diagnostic evaluation.

What is Pharmacogenomics?

Pharmacogenomics (PGx) is a science that attempts to take the guesswork out of how drugs will affect a person. It is research that is done via genetic testing to gauge how a person will respond to medications. The word pharmacogenomics comes a combination of the words pharmacology (the science of drugs) with the word genomics (the study of genes and gene functions).

Pharmacogenomics helps determine the most effective medication at the best dosage using the person's genetic information, called the genome. It is part of the broader healthcare field, known as precision medicine or personalized medicine.

Pharmacogenetics research helps healthcare providers better understand how to use medications in the treatment of neurological and psychiatric disorders.

How Does Pharmacogenomics Work?

Pharmacogenomics analyzes how DNA can influence the body’s response to medications. Pharmacogenomics may also determine if DNA can predict if the body will have an adverse reaction to a medication. DNA can also affect whether or not a medication will help a person or have no effect at all. In addition, DNA can help determine what the right dosage of an appropriate drug should be. Pharmacogenomics enhances a person’s health by letting them know before taking a medication, whether the drug will help or possibly cause harm. When a patient and their doctor know this type of information ahead of time, via DNA testing, it is much easier to prescribe drugs that work best for them.

What is DNA?

DNA (deoxyribonucleic acid) is the hereditary material found in humans. Just about all the cells in the body have the same DNA. The information in DNA is stored as code using different combinations of 4 bases (A, T, C, and G). Human DNA consists of about 3 billion bases. Approximately 99% of those bases are the same in everyone. The sequence of these bases determines the information available for building and maintaining a person.

DNA bases pair up with each other. A pairs with T and C pairs with G to form base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. A base with a sugar and a phosphate molecule is called a nucleotide.

Nucleotides that are organized into two strands forming a spiral-shape are called a double helix. The double helix looks similar to a ladder. Forming the ladder's rungs are the base pairs. The vertical sides of the ladder are constructed from the sugar and phosphate molecules.

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What is a Gene?

Genes are made up of DNA. In humans, genes range in size from a few hundred DNA bases to more than 2 million bases.2 It is estimated that humans have between 20,000 and 25,000 genes.2

Each individual has two copies of each gene, one inherited from each parent. Most genes are the same in everyone, but a small number of genes (less than 1%) are slightly different between people.2 These small differences are what give each person his or her unique physical features.

Pharmacogenomics is the study of how these inherited genetic differences impact the way drugs or medications affect a person.

The Right Medication Through Pharmacogenomics

Drugs interact with the body in many ways. How the drug is taken and where it interacts with the body are two critical processes. Once a drug is taken, the body has to break it down and transport it to the intended part of the body. A person's DNA can affect the numerous stages in this process to influence how the person responds to the medication. There are several ways these interactions can occur:

Drug receptors

Drup uptake

Drug breakdown

Using these factors, pharmacogenomics can help determine:

Whether a certain medicine will be effective

The best dosage for a person

Whether a drug will cause a serious side effect

Drug Receptors

Certain medications work by attaching to proteins that live on the surface of cells called receptors. A person’s DNA identifies the type and amount of receptors they have. The type and amount of receptors influence the response the body will have to a drug. Depending on these factors, a person may require a higher or lower dose of the medication compared to other people, or these factors may predict that a different medication is needed.

Drug Uptake

Some drugs need to be absorbed by the tissues and cells in which they act. A person’s DNA affects this process (uptake) with particular medications. If the uptake is lower than expected, this can mean the drug doesn't work well and can build up in other parts of the body, causing complications. The DNA can also determine how fast some medications are eliminated from tissues, and cells where they act. If drugs are eliminated too rapidly, they might not have time to do their job.

Drug Breakdown

DNA can affect how fast the body breaks down a medication. If a person’s body breaks the drug down more rapidly than most individuals, this means the body gets rid of the drug quicker. If this happens, more of the drug, or a different medication altogether, may be needed. If the body breaks the drug down more slowly, a person may require less of the drug to do its job.

Who Performs Pharmacogenomics Testing?

Initially, the cost of sequencing the human genome was very costly. The cost decreased from $3 billion in 2001 to under $1000 in 2016.3 Since the genomes of thousands of Americans have been typed, commercial genotyping is now available that can scan almost a million genetic variants, including those that can aid pharmacogenomics therapy. This has lowered the costs of such PGx tests to as low as $50.3

A healthcare practitioner can order for PGx testing to be performed. The two most common ways the test can be performed is by using blood or saliva. Once a sample is taken, it is sent off to a genetic testing lab.

For a Blood Test

A healthcare provider draws a blood sample using a small needle from a vein in the arm. A small amount of blood is drawn and stored in a vial or test tube. A blood draw typically takes less than five minutes.

For a Saliva Test

A healthcare provider will ask the patient to either spit into a test tube or will swab the inside of the patient’s mouth. The swab test is called a buccal smear that collects a sample of cells from the inside surface of the cheek. A person should not eat, drink, or smoke for 30 minutes before the test is performed.

What Does Pharmacogenomics Testing Tell a Healthcare Professional?

Pharmacogenetics testing for specific genes only needs to be performed once, because an individual's genetic makeup does not change over time. A test for a single gene or multiple genes may be ordered depending on the medication.

Pharmacogenomics results may be used by healthcare professionals to determine:

If the body will react negatively to certain medications

What medications will help achieve better outcomes

What dosages of medications are the most beneficial

How medications may interact with each other, both positively and negatively

Why is Precision, Personalized Medicine Important?

According to the Food and Drug Administration (FDA), costs associated with adverse drug reactions total $136 billion annually.4 Also, these adverse drug reactions cause 20% of the injuries or deaths annually to hospitalized patients. Precision medicine is important to avoid these risks that taking inappropriate drugs can cause.

Personalized medicine is also important because it can help a significant number of people. Large numbers of Americans take prescription medications. According to the FDA:

More than two-thirds of people get a prescription as a result of a healthcare visit. ​​​4

About 2.8 billion prescriptions were filled in the year 2000 alone. That works out to 10 prescriptions per American. ​​​4

When someone is taking 4 or more drugs, the risk for adverse drug reactions increases exponentially. ​​​4

While healthcare professionals need to reduce the number of medications a person is taking when appropriate, in many cases doing so would cause a person harm. For this reason, it is vital to understand how medications interact with a person, and PGx testing can help in this area. PGx testing allows a doctor to make the most informed decision when prescribing drugs and in avoiding preventable adverse drug reactions.

Precision Medicine and Mental Health Disorders

PGx testing can be useful in determining the right medications for mental health disorders, such as depression. Studies have found that about 30% to 50% of people who are prescribed their first antidepressant medications do not respond well to them.5 This can have severe negative impacts on a person's mental health because it can take a few months to a few years to find the right medication to relieve the person's depression symptoms. During this trial period, the person suffering from depression is dealing with the damaging effects of depression, as well as being exposed to ineffective drugs.

Research suggests that genetics plays a role in the unresponsiveness some people have to certain antidepressants. PGx testing to prescribe more effective antidepressants can help better treat depression symptoms as well as decrease the adverse effects inappropriate drugs can cause.

How Does DNA Testing Help a Medical Team?

DNA testing can help a medical team in a variety of ways.

DNA testing has potential benefits in determining if a person has gene mutations.

DNA test results can help give a person peace of mind when they are uncertain about how to proceed in healthcare decisions. With DNA test results, it's possible to make informed decisions about managing healthcare.

In some cases, DNA test results can eliminate the need for unnecessary checkups and other screening tests.

Results from a DNA test can inform a person on how to prevent and monitor certain conditions. It can also help inform treatment options.

People thinking about having children can be helped by DNA test results.

DNA testing on newborns can help with early identification on genetic disorders, so treatment can begin as soon as possible.

Drug Interactions

DNA testing can also help a medical team regarding drug interactions. Drug interactions are especially important because there are many different ways drugs can interact with the body and with each other.

Drug interactions can happen even before the medications enter the body because they are incompatible with a person’s system. Drug interactions can occur at any point when the body is absorbing, distributing, metabolizing, or eliminating the drugs. For example:

Drugs can bind to each other in the gastrointestinal tract, which can prevent absorption and availability.

Interactions that happen in the liver and gastrointestinal tract can change the rates that the body metabolizes the drugs. It can either speed it up or inhibit the metabolism process.

If several drugs compete at the site of drug transportation, interactions can develop.

Interactions can also happen at the level of drug action. For example, there are FDA warnings for taking any beta-blocker along with any calcium channel blocker because this can slow the heart rate and cause a heart block. In practice, most health care providers know that these two classes of drugs are often used successfully and safely in people with hypertension. This conflict between drug interaction warnings and actual use can cause distrust in warnings.

PGX testing can help clear up these types of issues.

PGx Testing Examples

The benefits of PGx testing can be seen in the following examples:

Warfarin: Before PGx testing, many people taking Warfarin to prevent blood clots, which is prescribed 21 million times annually, were at risk.6 If they were to take too little of the drug, it could cause more blood clots. If they were to take too much of the drug, it could cause excessive bleeding.

In 2007, the FDA recommended PGx testing for people where Warfarin was being considered to help their conditions.7 Pharmacogenomics testing helps healthcare professionals determine which people are expected to benefit from taking Warfarin and at what dosage.

Opioids for Pain Management: Another example of PGx testing helping people is in determining the levels of opioids needed for effective pain relief.8 Different people metabolize pain medications at different rates. People with a slower metabolism of opioids may build up dangerously high levels of opioids in the body, causing adverse events such as addiction. Knowing a person's metabolism patterns through PGx tests helps determine optimal dosing that controls pain but also radically reduces the risk of addiction.

PGx tests also aid healthcare professionals in recognizing that some people may need a higher dose of painkillers to experience pain relief. For example, people who rapidly metabolize opioids may not experience pain relief, but if they ask for higher doses, it may be assumed that they are abusing the drug.

The testing procedure

The benefits of DNA testing

The limitations of the DNA test

The possible consequences of the results

Going through all these steps for testing is called informed consent. This means that a person has enough information to make an educated decision about DNA testing. "Consent" means they agree to have the test performed.

Informed consent for DNA testing is typically obtained by a doctor or healthcare professional during an office visit. The healthcare provider will discuss the test and answer any of the patient’s questions. If the patient then wishes to proceed, they will read and sign a consent form.

Informed Consent Form

An informed consent form includes:

A general description of the test

The purpose of the test

The condition for which the test is being performed

How the test will be performed (i.e. blood or saliva sample)

What the test results mean, either positive or negative results

The possibilities of results that lack useful information

The potential for incorrect results (i.e. false positives or false negatives)

Any physical or emotional risks associated with DNA testing

If the results may be used for research purposes

What happens to the test specimen once testing is over

The different aspects of informed consent may vary by the state, because some states have specific laws on what must be included.

Paying for DNA Testing

Many health insurance plans include coverage for genetic testing when it is recommended by a doctor. A person should check with their health insurance carrier before having testing done because each company has different policies about covering DNA testing.

In some cases, a person may decide not to use their health insurance to pay for testing costs. If the results of the tests are revealed to the health insurance carrier, a person’s insurance coverage may be affected. Another option is to pay for the test out-of-pocket. A state's privacy protection laws may prohibit revealing DNA test results to an insurance company before they cover the costs. A person can check their state laws to see if this is true where they live.