What Do I Need to Know About Drug Interactions?

Published: March 28, 2023
By Tierra Jackson, 2023 PharmD Candidate

Chemical reactions happen all around us every day. There are natural reactions that exist in the air, in our food, and even in our bodies to keep us healthy. When we take medications, this introduces a change to our body's natural function. When we take multiple medications, there is a potential that the drugs can interact with each other. Drug interactions can change our body's response for better or worse.

How does my body process medication?
The term pharmacokinetics describes what your body does to a drug. The commonly used abbreviation for the process is ADME. Medications are absorbed into our system, distributed to their intended place of action, metabolized to activate, or deactivate, and eliminated or removed from our bodies.

Enzymes in our bodies activate or deactivate medication (or substrates) in the metabolism stage to make them easier to eliminate. Drug interactions impact this metabolism by increasing or decreasing the amount of enzyme present.

How do drugs affect this process?
Drug-drug interactions can happen in a few different ways. One is that drugs can change the acidity in your stomach causing medications to not be absorbed well. An example of this is when we take antacids, like Tums, which may prevent some antivirals used to treat HIV, like dolutegravir, from being absorbed well and not be as effective against the virus. A similar example is when certain vitamins or minerals that are present in supplement bind with the drug and keep it from being absorbed. An example of this is when iron supplements are taken with certain antibiotics, like levofloxacin, which prevent them from being completely absorbed and the antibiotic may not work as well.

Drug-drug interactions can also occur when drugs impact the way the enzymes work in your body. Drugs can bind to the enzymes and either stimulate them to metabolize medications faster or prevent them from metabolizing medications as well. An example of drugs that stimulate metabolism are anti-seizure medications like phenytoin or phenobarbital while anti-fungal agents like fluconazole are known for blocking metabolism.

When medications induce the enzymes, they may cause the body to get rid of the medications more quickly than expected making the medicine not work as well. When medications inhibit the enzymes, it may slow down the body’s process to remove the drug leading to higher levels of the drug in the body than expected. In some cases, this is done on purpose but most of the time, it could lead to unwanted side effects.

Can certain foods interact with drugs?
Yes! Foods can impact how drugs work in similar ways that drugs do. Some examples of common food interactions are the following:

  • Grapefruit and grapefruit juices are classified as inhibitors and can block the metabolism of common medications like statins, for cholesterol. It is recommended to avoid consuming grapefruits with these medications all-together.
  • Calcium-rich foods and calcium containing supplements can decrease the absorption of many medications including antibiotics, anti-hypertensives, and others. It is recommended to take any medication 2 hours before taking an antacid.
  • Alcohol consumption can have toxic interactions with several medications. Mixing alcohol with acetaminophen can produce a toxic product that damages the liver. Mixing alcohol with medications that alter a person’s cognition can have an additive effect. Mixing alcohol with some antibiotics like metronidazole can cause a disulfiram reaction that can cause nausea, dizziness, tachycardia, and more.

How can I prevent drug interactions?

  • Pay close attention to instructions, and warning labels on your medication bottles. They can offer insight into potential interactions from foods or other medication.
  • Notify your pharmacist and providers about medications you are taking (prescription and over-the-counter (OTC)) before starting or changing any medications. Keep a list of your medications, including prescriptions, OTC, and herbals, and bring it to all visits with your provider.

How can my pharmacist help me prevent drug interactions?
Your pharmacist can check for drug interactions and advise you on how to handle it. They can also tell you how to monitor for efficacy changes or side effects that may occur as a result of a drug interaction.

Drug interactions can have a negative impact on your response to therapy. However, by being aware, keeping a list of ALL of your medications (OTC, prescription, vitamins, and herbal supplements), including those you take just “sometimes,” and making sure you communicate with your pharmacist or doctor, the risks can be minimized so that all of your medications can remain safe and effective.

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