Ondansetron is a medication used in preventing nausea and vomiting caused by the action of cancer treatment. Cancer treatment, whether chemotherapy (cancer drug treatment), radiation therapy, or surgery can leave a patient feeling nauseated. Nausea and vomiting urge caused by cancer treatment is usually a serious condition that can disrupt an individual’s daily activities. Ondansetron is therefore indicated as a medication for the management of nausea and vomiting caused by chemotherapy and radiotherapy. It is also employed in the treatment of postoperative nausea and vomiting (PONV).

Ondansetron belongs to the section of drugs known as serotonin 5-HT3 receptor antagonists. They are known as antiemetics, they act on the body system to block nausea and vomiting. The medication basically targets the after-surgery syndromes. It is used to manage and prevent nausea and vomiting induced by cancer treatment. Ondansetron can also be employed in the treatment of gastroenteritis and can be used to treat vomiting caused by motion sickness. It can be administered orally or through the intramuscular route of administration.

The mechanism of action of Ondansetron is through an inhibition reaction. It blocks or inhibits the action of the chemicals that can trigger nausea and vomiting. Serotonin is a natural chemical in the brain and it is known to contribute to nausea and vomiting. Ondansetron blocks the actions of this chemical to relieve a patient of nausea and vomiting. This medication may also be used to prevent the complication of shivering in individuals who just had anesthesia.

Ondansetron is a specific and selective serotonin 5-HT receptor antagonist. These serotonin 5-HT 3 receptors are located at the nerve endings of the Vagus centrally and peripherally in the chemoreceptor trigger zone of the postrema. There is a temporal relationship between the action of emetogenic drugs and the serotonin release. The emetogenic action shows that serotonin is released by chemotherapeutic agents from the enterochromaffin cells of the small intestine which causes degenerative changes in the gastrointestinal tract.

The serotonin released in turn stimulates the vagal and splanchnic nerve that supplies innervation to the gastrointestinal tract. The Vagus and Splanchnic nerve receptors then project into the medullary vomiting center along with the 5-HT receptors in the postrema. This mechanism is known as the vomiting reflex which brings about nausea and vomiting. So, Ondansetron works to block the initiation of the vomiting reflex.

Absorption of Ondansetron takes place in the gastrointestinal tract. Ondansetron undergoes the first-pass metabolism. Following administration of the 8mg tablet, bioavailability may range from 56% to 60%. Food enhances the bioavailability of ondansetron. The volume of distribution of ondansetron is approximately 160L. Plasma protein binding of ondansetron is approximately 73%.

Ondansetron is a substrate for human hepatic Cytochrome P450 enzymes including the CYP1A2, CYP2D6, and CYP3A4. considering the overall turnover for ondansetron, CYP 3A4 has a predominant role to play. After administration, whether oral or intramuscular, ondansetron is extensively metabolized and eliminated in the urine and faeces. Less than 10% of ondansetron dose is eliminated unchanged from the body. The major urinary metabolizing agents are 45% glucuronide conjugates, 20% sulphate conjugates, and 10% hydroxylation products.

Ondansetron uses

This medication is used to prevent nausea and vomiting induced by (chemotherapy) cancer drug treatment and radiation therapy. It blocks serotonin, a natural substance in the body that causes vomiting. Ondansetron has the following medical uses:

Cancer treatment

Ondansetron is a 5-HT 3 receptor antagonist usually prescribed as a primary medication for cancer patients. It is used to prevent chemotherapy and radiotherapy-induced nausea and vomiting. It is indicated as a treatment for nausea and vomiting caused by cytotoxic chemotherapy and radiotherapy.

Postoperative medication

Patients who have just had a surgical procedure for cancer treatment are prone to nausea and vomiting. Ondansetron is a very effective way of controlling post-surgical or post-operative nausea and vomiting. It’s most suitable for the management and treatment of nausea and vomiting compared to other drugs. It is more effective compared to metoclopramide and less sedating than droperidol or cyclizine.


Ondansetron is used as an off-label medication to treat hyperemesis gravidarum and morning sickness in pregnancy. It is usually resorted to upon a failed trial of other drugs. Ondansetron use by pregnant mothers may not have an adverse effect on the baby during pregnancy but it may be a risk of a heart problem in infancy.


Ondansetron is employed in the treatment of vomiting associated with gastroenteritis and dehydration. It has been much helpful in gastroenteritis condition as it helps to reduce the need for hospitalization. The use of ondansetron to reduce vomiting in gastroenteritis and dehydration has helped to reduce the rate at which people visit the emergency department.

Ondansetron  8mg

Ondansetron 8mg is the strength of Ondansetron to be taken at once. There is an 8mg tablet that can be used orally. Ondansetron 8mg contains the necessary concentration to serve as an inhibitory drug for nausea and vomiting. 8mg tablet of ondansetron is effective enough to prevent nausea and vomiting.

Ondansetron dosage

A patient can take Ondansetron with or without food. The first dose of ondansetron is usually taken before the surgical procedure, chemotherapy, or radiation treatment. Ondansetron oral tablet comes as 8mg. 8mg ondansetron is effective to treat nausea or vomiting.

Doctors would normally administer 8mg ondansetron to patients 30 minutes before chemotherapy and other cancer treatment. Patients may be required to take additional doses for up to three times a day during treatment or be required to take for a few more days after treatment of cancer.

For chemotherapy treatment, a Daily dose of 16 to 24 mg is required daily. For the prevention of nausea and vomiting after surgery, an adult can take 26mg before surgery. It should be administered in a dose of 5mg/m via the intravenous route. The dose for intravenous route must not exceed 8mg. An oral dose can start twelve hours after surgery and can last up to 5 days. The total daily dose for ondansetron must not exceed 32mg.

Dosage can be based on the patient’s medical condition and response to therapy. The dose for children may be based on factors like age and weight. Patients with liver problems are advised to take 8mg per day.

Precautions to take when using Ondansetron

Ondansetron should be dissolved on top of the tongue and not to be swallowed or chewed. Patients should keep the tablet in its blister pack until the drug is ready to be used. Ensure that you do not push the tablet through the foil, this may damage the tablet. Instead, open the package and pull the foil backwards.

Ensure that your hands are dry before touching the tablet. Dry your hands before using ondansetron. It usually comes in a blister pack or in a bottle. Place the medication on your tongue to dissolve. This should be done immediately after the medication is been removed from the blister or bottle. Allow medication to dissolve completely on the tongue before swallowing. You do not need to take ondansetron with water as this may cause you to get a headache.

To prevent nausea and vomiting from chemotherapy, ondansetron should be taken 30 minutes before the start of treatment. To prevent nausea and vomiting from radiation treatment, ondansetron should be taken 1 to 2 hours before the surgery.

Safety of ondansetron during pregnancy is not yet established, so the use of pregnant women is not recommended. However, some persons use it to treat morning sickness in pregnancy. Breastfeeding mothers are also not advised to use Ondansetron. Studies have shown that it passes into the milk of lactating mothers and it is not safe for infants.

Ondansetron  side effects

Many medications would normally have side effects because they are foreign compositions or synthesis used to take corrective measures in the body system. The side effect of a drug is an undesired or unwanted reaction of the drug even when it is taken in normal dose. Side effects are the reaction or responses you give upon taken ondansetron.

Side effect or response to a drug may either be mild or severe. The side effect can also be either permanent or temporary for some drugs. The side effect of ondansetron can be mild or severe. Not everyone would experience side effects with the use of ondansetron while it would normally occur in some people. You do not need to get worried about the side effect because you may not experience them, you only need to know them so that you can understand the reason behind how you feel and how to take proper measures on time.  The common side effect a patient may experience after using Ondansetron include;

Fatigue: it may cause a feeling of general tiredness and weakness in the body. Use may lead to weakness. It may cause the patient to feel tired all day. When on this medication, patients are advised to get enough rest.

Constipation: A problem may occur with bowel motility. A patient may find it difficult to pass stool which may lead to a feeling of discomfort.

Headache: may cause a condition of discomforting headache.

Dizziness:  A patient experiencing dizziness as a side effect of ondansetron. intake may cause a feeling of lightheadedness, loss of balance, wooziness or heavy-headedness, feeling faint,  and spinning or a false sense of motion.

Rash: Ondansetron may cause rashes, skin redness, itchiness, scaly, dry, crusted skin with fluid-filled blisters.

These are mild side effects that you may not need to worry so much about. They would normally go away after a little while.

The following are some of the adverse effects of ondansetron that may require emergency or may require you to discontinue use.

Blurry vision or loss of vision: Ondansetron use may cause patients to have blurry vision. Patients lose the sharpness of eyesight, vision becomes hazy and out of focus. Object come out of focus and movement may be a little difficult. Blurry vision that comes with the use of ondansetron is nothing serious. It will decrease rapidly with time.

Seizure: prolonged use of ondansetron may alter nervous functions. Nervous disorders caused by ondansetron use is more common than immune disorders.

Chest pain: Ondansetron may cause some feeling of discomfort for patients.

Loss of consciousness: use of this medication may alter the nervous system and make the patient fall into a state of unconsciousness.

Immune system disorder: it may cause hypersensitivity to a drug which may result in face oedema, anaphylactic shock, angioedema. Immune disorders are rare, it may be as a result of cross-sensitivity with other 5-HT3- antagonists.

Hives, Severe rash that causes blisters and peeling

Difficulty breathing, talking or swallowing.

Ondansetron drug interactions

Ondansetron cannot be used with a few other drugs as they can either delay or decrease its absorption and action, or in the worse case, give an adverse effect. Some drugs may have an effect on the way ondansetron works, and ondansetron may also affect the action of other drugs you are taking. The following are drugs that may interfere with the action of Ondansetron:

Other serotonin 5-HT3 antagonists: this is a class of drug that is generally used to treat or prevent post-surgical nausea and vomiting. They include Lotronex, Kytril, Anzemet, and Alicia.

Antibiotics: there are some antibiotics whose actions are not suitable for ondansetron activity. Using them together can cause some adverse effects. These antibiotics include erythromycin (E.E.S., Erythrocin) and clarithromycin (Biaxin, in Prevpac).

Medications for heart conditions: some of these medications disrupt the action of ondansetron which may lead to undesired effects. They include amiodarone (Pacerone, Cordarone ),

Beta blockers: these drugs are used to lower the heart rate. They include acebutolol (Sectral),  atenolol (Tenormin), and bisoprolol (Zebeta).

Tramadol: is usually used as a pain killer. The action of Tramadol is not compatible with ondansetron. An example is Ultram.

Antiseizure medications like phenytoin (Dilantin).

Medications to treat irregular heartbeat, such as dofetilide ( Tikosyn), amiodarone (Cordarone, Pacerone), disopyramide (Norpace).

Some antipsychotic medications like thioridazine (Mellaril), mesoridazine (Serentil), and haloperidol (Haldol).

Anti-depressants like venlafaxine ( Effexor ) and amitriptyline (Elavil).