Acetaminophen is one of the most commonly used medicines in the world. Many people take it when they have a headache, a fever, or mild pain. You might recognize it under brand names like Tylenol or Panadol.
Usually, we take acetaminophen by swallowing a pill or a tablet. It is considered very safe when used as directed, which is why it is available in most homes without a prescription.
In hospitals, however, doctors sometimes give acetaminophen differently. Instead of giving a pill, they deliver it straight into the bloodstream using a needle. This is called intravenous, or IV, delivery. There are good reasons for this.
When acetaminophen is given through an IV, it works faster because it goes directly into the blood. It is also easier for medical staff to control the exact amount of medicine a patient gets, and it is helpful for patients who are too sick to swallow pills.
But researchers have recently found something surprising about using acetaminophen this way. When given by IV, acetaminophen can cause a noticeable drop in blood pressure. This drop is not just seen in very sick patients; it can happen to anyone who receives the medicine this way.
In one study, about six out of every ten critically ill patients who received IV acetaminophen had their blood pressure fall significantly. About a third of those patients needed extra medical help because of the blood pressure drop. Even though this side effect can be serious, acetaminophen is still used a lot in hospitals because it is generally safe and effective.
Scientists wanted to understand why this drop in blood pressure happens. A research team led by Thomas Qvistgaard Jepps at the University of Copenhagen carried out a study to find out. They discovered that when acetaminophen is given through an IV, it behaves differently in the body compared to when it is taken as a pill.
Normally, when you swallow acetaminophen, it first passes through the liver, which changes the drug slightly before it spreads through the body. But when it is given directly into the blood, it skips the liver at first. This leads to the creation of different chemicals in the bloodstream.
These new chemicals seem to affect potassium channels. Potassium channels are small structures in the walls of blood vessels that help control how wide or narrow the vessels are, and therefore help regulate blood pressure.
When these potassium channels are affected, blood vessels can relax too much, causing blood pressure to fall. In their experiments with rats, the researchers were able to block these potassium channels, and this prevented the sudden drop in blood pressure.
This discovery is important for doctors and nurses, especially during times when many patients need IV acetaminophen, such as during the COVID-19 pandemic when hospitals were full. It gives them a better understanding of what to watch for and how to possibly prevent problems.
For everyday people who take acetaminophen as a pill at home, there is no need to worry about this side effect. The problem only happens when the drug is given directly into the blood. As long as you follow the instructions on the label and don’t take too much, acetaminophen remains a very safe way to treat mild pain and fever.
This study adds to what we know about how medicines can behave differently depending on how they are given. It reminds us that even familiar drugs can act in unexpected ways under different conditions. The full study was published in the journal Atherosclerosis, Thrombosis, and Vascular Biology.
If you care about high blood pressure, please read studies about breakfast for better blood pressure management, and the gut feeling that lowers blood pressure.
For more health information, please see recent studies about how the dash diet helps lower blood pressure, and how to eat your way to healthy blood pressure.
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