A simple explanation of a medication for nausea and vomiting: Serotonin Antagonist

Nausea and vomiting caused by anesthesia during chemotherapy, radiation therapy, or surgery are a big problem for many people. The discomfort you feel at times like these is overwhelming. So today we are going to talk about a special type of medication that your doctor will give you to control this condition. These are called serotonin antagonists . Let's see what these medications are, how they work, and what we need to be aware of when using them.

What is this serotonin antagonist?

Simply put, these are a group of medications prescribed by a doctor to prevent and treat nausea and vomiting. In medical terms, we call antiemetics the medications that are given for nausea. So, serotonin antagonists are one such group of medications.

This class of drugs is known by several other names:

• Serotonin-receptor antagonists
• 5HT3 receptor antagonists
• Serotonin blockers

Although these names may seem a bit complicated, they all mean the same thing. That is, they block a chemical called serotonin in our body at some point. We will talk about that more clearly a little later.

What are the main types of medicines in this category?

There are several types of medications in this category. Your doctor may have prescribed one of these to you. These can be taken as pills or as injections.

Among these , Ondansetron (Zofran®) is one of the most commonly prescribed medications by doctors to stop nausea, both in Sri Lanka and around the world.

In what situations is this medicine used?

This medication is primarily approved to prevent nausea and vomiting caused by certain treatments.

Mainly approved uses:

• Nausea caused by chemotherapy: When anti-cancer drugs enter the body, there is a high chance of nausea and vomiting. These medications are very helpful in preventing it.
• Nausea caused by radiation therapy: Nausea can also occur during radiation therapy to destroy cancer cells. These are also given for those cases.
• Post-surgery nausea: This medication is also used to control nausea and vomiting caused by the effects of anesthesia after surgery.

This medicine is given appropriately to both adults and children.

Other uses (Off-label use):

Sometimes, doctors, based on their medical experience, prescribe these medications for conditions other than those for which they are approved. We call this 'off-label use'.

• Treating nausea after surgery: This medication is given to prevent nausea and also after it occurs.
• Morning sickness: Some people experience more severe nausea and vomiting during early pregnancy. If other treatments are not effective, this medication may be given under the close supervision of a doctor.

How does this medicine work? Let's take a look at it scientifically.

To understand this, we first need to simply understand what 'serotonin' is and what 'serotonin receptors' are.

Think of it this way: serotonin is a messenger, or neurotransmitter, in our bodies. This messenger helps regulate many things, including our mood, sleep, and digestion. Surprisingly, 90% of this serotonin is found in the walls of our stomach and intestines (gastrointestinal system).

Now, how does nausea occur? Due to something like cancer treatment, cells in our intestines suddenly release a large amount of serotonin. This excess serotonin binds to receptors in the intestines and sends a message to the brain that "something unusual is happening here." The brain interprets this message as "nausea."

So what does the 'serotonin antagonist' drug we give you do? This drug is like a wrong key in a lock. It fits into the lock (receptor), but it doesn't activate the lock. Also, because it's inside the lock, it doesn't allow the right key (serotonin) to come in and connect to the lock.

That is, this medicine blocks the 5-HT3 receptors that serotonin binds to. This means that the excess serotonin has nowhere to go and bind to. As a result, the nausea message to the brain stops, and the feeling of nausea and vomiting decreases.

What are the most common side effects?

Like any medicine, these medications can cause some minor side effects, but these are usually not serious.

If these side effects are very bothersome to you, talk to your doctor about it.

Are there any special risks to watch out for?

Although this type of medication is generally very safe, there are a few things we need to be especially careful about.

Heart Issues

Doctors are very careful when giving this medication to people with certain heart conditions because it can have a small effect on the rhythm of the heart. If you have any of the following conditions, be sure to tell your doctor.

• Long QT syndrome
• Heartbeat irregularities (Ventricular arrhythmia)
• Any other type of heart disease

Serotonin Syndrome - This is very important!

This is a serious, but very rare, condition that occurs when serotonin levels in our body become excessively high.

This risk may increase if you take other medications that affect serotonin levels (such as some antidepressants) while taking serotonin antagonists. This is because when these medications block serotonin receptors, the amount of serotonin free in the blood increases.

It is extremely important to inform your doctor if you are taking the following medications:

• SSRIs
• SNRIs
• Mirtazapine
• Monoamine oxidase inhibitors (MAOIs)

What are the symptoms of serotonin syndrome? These symptoms can range from mild to severe.

Use during pregnancy (Pregnancy)

These medications are not associated with a significant risk of birth defects in the fetus when used during pregnancy. However, a small increase in the risk of certain birth defects of the heart and brain has been reported. Therefore, if you need these medications during pregnancy, your doctor will discuss the benefits and risks with you at length before making a decision.

When should I call my doctor?

If you continue to use this medication, it is important to see your doctor at regular intervals to check the effectiveness of the medication. In addition, talk to your doctor in the following situations:

• If side effects bother you: If things like headaches and constipation are too bothersome to control.
• If nausea and vomiting do not subside: If nausea does not subside or worsens despite taking medication.
• If you want to stop taking the medication: Never stop taking the medication without asking your doctor.

Nausea is a really annoying thing. But the good news is that there are effective medications, such as serotonin antagonists, to control it. If you have any questions about this, don't be afraid to ask your doctor.