Acetaminophen, also called paracetamol in many countries, is one of the most commonly used pain-relieving and fever-reducing medicines in the world.
Millions of people take it at home for headaches, muscle pain, toothaches, fever, and many other common health problems.
When used at the recommended dose, it has a long history of being considered a safe and reliable medicine.
Most people take it as tablets or liquid by mouth, but hospitals also give it directly into a vein through an intravenous (IV) drip when patients cannot swallow medicine or need pain relief very quickly.
Doctors often choose intravenous acetaminophen for patients who have just had surgery, are seriously ill, or are being treated in intensive care units. Giving the medicine through a vein allows it to work faster than tablets and helps healthcare workers give an exact dose. It also makes sure patients who are unconscious, vomiting, or unable to swallow still receive pain relief.
Even though intravenous acetaminophen is widely used, doctors have known for many years that it can sometimes cause blood pressure to fall suddenly for a short time.
This drop can be mild in some people but much more serious in others. Earlier reports showed that the problem is especially common in critically ill patients, although it has also been seen in healthy volunteers receiving the medicine through a vein.
A new study from the University of Copenhagen has now helped explain why this happens. The researchers wanted to understand the biological reason behind this side effect instead of simply observing that it occurs. Their work offers new clues that may eventually help doctors reduce this risk while continuing to use the medicine when patients need it.
The research found that about six out of every ten critically ill patients experience a noticeable drop in blood pressure after receiving intravenous acetaminophen.
Around one-third of these patients need medical treatment to bring their blood pressure back to a safe level. Although this sounds concerning, doctors still use the medicine because its benefits often outweigh the risks when patients are carefully monitored.
The team discovered that the body handles acetaminophen differently depending on how it enters the body. When a person swallows a tablet, the medicine first passes through the liver, where much of it is processed. However, when it is given directly into a vein, it bypasses this first step. As a result, different breakdown products are produced in the body.
These breakdown products appear to affect tiny structures called potassium channels. These channels help control whether blood vessels become narrower or wider. When blood vessels relax and become wider, blood flows more easily and blood pressure falls.
The researchers found evidence that the breakdown products created after intravenous acetaminophen can influence these channels, causing blood vessels to relax more than usual and leading to the sudden fall in blood pressure.
To test their idea, the scientists carried out experiments in rats. They used medicines that block certain potassium channels before giving intravenous acetaminophen.
The results showed that blocking these channels greatly reduced or even prevented the sharp drop in blood pressure. This suggests that the potassium channels play an important role in producing this side effect.
The findings could eventually help researchers develop new ways to make intravenous acetaminophen safer for patients who need it. In the future, doctors may be able to protect vulnerable patients by targeting these channels or by developing new treatment approaches based on this discovery.
The researchers also stressed that the findings should not worry people who take acetaminophen tablets at home. The newly identified effect is linked to intravenous treatment rather than the usual oral form taken for everyday pain or fever. For most people, acetaminophen remains safe when it is used according to the recommended instructions.
This research is especially important because intravenous acetaminophen is commonly used in hospitals around the world to treat pain and fever in patients with serious illnesses. Understanding why the medicine sometimes lowers blood pressure may help improve patient care and reduce complications during treatment.
The study was led by Thomas Qvistgaard Jepps from the University of Copenhagen and was published in the journal Atherosclerosis, Thrombosis, and Vascular Biology.
The discovery provides a clearer explanation for a long-recognized side effect and opens the door to future research aimed at making this widely used hospital medicine even safer for patients who depend on it.
If you care about blood pressure, please read studies about how diets could help lower high blood pressure, and 3 grams of omega-3s a day keep high blood pressure at bay.
For more health information, please see recent studies that beetroot juice could help reduce blood pressure, and results showing cinnamon could help lower high blood pressure.
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