Acetaminophen, also known as paracetamol, is one of the most commonly used pain-relieving and fever-reducing medicines in the world.
Millions of people take it safely every day for headaches, muscle pain, toothaches, fever, and many other common health problems. Most people take acetaminophen as a tablet or liquid by mouth.
However, in hospitals, doctors often give it through an intravenous (IV) drip directly into a vein, especially for patients who cannot swallow medicine after surgery or because they are seriously ill.
Giving acetaminophen through an IV has several advantages. The medicine starts working much faster than tablets because it goes directly into the bloodstream. Doctors can also control the exact dose more accurately, making it useful for patients in intensive care units or those recovering from major operations.
Even though IV acetaminophen is generally considered safe, doctors have noticed an important side effect in some patients. Soon after receiving the medicine, their blood pressure suddenly drops.
Blood pressure is the force of blood pushing against the walls of the arteries. If it falls too low, the body’s organs may not receive enough oxygen-rich blood. This can be especially dangerous for patients who are already critically ill.
Researchers at the University of Copenhagen wanted to understand why this unexpected drop in blood pressure happens. Their findings provide new clues that may help doctors prevent this side effect while continuing to use the medicine safely.
Previous research has shown that about six out of every ten critically ill patients experience some drop in blood pressure after receiving IV acetaminophen.
For around one-third of these patients, the decrease is severe enough that doctors need to provide additional treatment to raise blood pressure again. Despite this, IV acetaminophen remains widely used because its overall benefits usually outweigh the risks when patients are carefully monitored.
The research team discovered that the way the body processes acetaminophen depends on how the medicine enters the body. When people swallow a tablet, the drug first passes through the liver before entering the rest of the bloodstream.
However, when acetaminophen is given through an IV, it bypasses this first step in the liver. As a result, different chemical byproducts are produced as the body breaks down the medicine.
The scientists found that some of these byproducts affect tiny structures called potassium channels. Potassium channels help control how muscles in blood vessel walls behave. They play an important role in deciding whether blood vessels become narrower or wider.
When these channels are activated too strongly, blood vessels relax and widen more than normal. As the blood vessels widen, blood pressure can fall quickly.
To test whether these potassium channels were responsible, the researchers carried out experiments in rats. They gave the animals a medicine that blocks specific potassium channels before administering IV acetaminophen.
The animals experienced a much smaller drop in blood pressure than expected. This finding suggests that these channels play a major role in causing the side effect.
Although more research is needed before this approach can be used in people, the results raise the possibility that future medicines could help prevent dangerous drops in blood pressure in patients receiving IV acetaminophen.
The researchers emphasized that these findings mainly apply to acetaminophen given through a vein in hospital settings. They do not suggest that people should stop taking acetaminophen tablets or liquid at home. When taken by mouth at the recommended dose, acetaminophen has a long history of safe and effective use for treating pain and fever.
The findings are especially valuable because IV acetaminophen is commonly used in intensive care units and became even more widely used during the COVID-19 pandemic to help control fever and pain. A better understanding of its side effects may allow doctors to identify patients at higher risk and improve their care.
The study was led by Thomas Qvistgaard Jepps and published in the journal Atherosclerosis, Thrombosis, and Vascular Biology. The research provides important new insight into how a familiar medicine affects the body and may help make hospital treatment even safer in the future.
If you care about blood pressure, please read studies about unhealthy habits that could increase high blood pressure risk, and people with severe high blood pressure should reduce coffee intake.
For more information about blood pressure, please see recent studies that early time-restricted eating could help improve blood pressure, and results showing plant-based foods could benefit people with high blood pressure.
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