What is the Difference Between Ondansetron and Metoclopramide

The key difference between Ondansetron and Metoclopramide is that Ondansetron is a selective serotonin receptor antagonist (5-HT3 antagonist) used to treat nausea and vomiting, while Metoclopramide is a dopamine receptor antagonist and a prokinetic agent used to treat nausea vomiting.

Ondansetron and Metoclopramide are different medications used to treat nausea and vomiting. These medications are available as oral tablets, oral liquids, and injectable forms. Although they have similar indications, they are different in various aspects. Ondansetron is a selective serotonin receptor antagonist that blocks the action of serotonin to prevent nausea and vomiting. In contrast, Metoclopramide is a dopamine receptor antagonist and prokinetic agent that blocks the action of dopamine to prevent nausea and vomiting. In addition, Metoclopramide is also effective in treating gastroparesis, a condition in which the stomach does not empty properly. Both these drugs are well tolerated and effective in managing the symptoms. The best medication for the individual need should be decided after considering the patient’s conditions by a qualified healthcare provider.

CONTENTS

1. Overview and Key Difference
2. What is Ondansetron  
3. What is Metoclopramide
4. Similarities – Ondansetron and Metoclopramide
5. Ondansetron vs. Metoclopramide in Tabular Form
6. Summary – Ondansetron vs. Metoclopramide

What is Ondansetron?

Ondansetron is a serotonin 5-HT3 receptor antagonist prescribed to prevent nausea and vomiting associated with cancer chemotherapy drugs. During chemotherapy, serotonin will release from the enterochromaffin cells of the small intestine, initiating the vomiting reflex. Ondansetron displays a higher affinity towards serotonin receptors, with a lower affinity for dopamine receptors, thereby blocking the initiation of the nausea and vomiting reflex.

Ondansetron may be given orally or intravenously, depending on the dose of the chemotherapeutic drug used. The gastrointestinal tract absorbs the orally administered Ondansetron, and then the drug undergoes hepatic first-pass metabolism. The drug is bound with plasma proteins approximately 73% and extensively metabolized by cytochrome p450 enzymes in the liver. Then the metabolites are excreted in urine and feces, while 10% of the unchanged drugs are found in urine. The half-life of the Ondansetron is approximately 3-4 hours.

What is Metoclopramide?

Metoclopramide is an antiemetic dopamine D2 receptor antagonist prescribed to treat gastroesophageal reflux disease, acute and recurrent diabetic gastroparesis. In addition, the drug is often prescribed for gastric bezoars, intractable hiccups, and migraine pain as the off-label uses. Administration of Metoclopramide results in the inhibition of both presynaptic and postsynaptic D2 receptors and promotes the release of acetylcholine, accelerating gastric emptying and transit through the gut. In addition, Metoclopramide can also agonize serotonin 5-HT4 receptors and antagonize muscarinic receptor inhibition.

Metoclopramide is primarily administered orally, intravenously, and in nasal sprays. After oral administration, Metoclopramide is rapidly absorbed in the gastrointestinal tract with an absorption rate of 84%, but the bioavailability is approximately 40%. The plasma protein binding ability of the drug is comparatively low; therefore, the tissue distribution is comparatively high. After the absorption, Metoclopramide undergoes first-pass metabolism by cytochrome p450 enzymes. After being metabolized, Metoclopramide is mainly excreted by urine with an elimination half-life of 5-6 hours. The overdose symptoms of Metoclopramide include drowsiness, disorientation, and extrapyramidal reactions.

What are the Similarities Between Ondansetron and Metoclopramide?

• Ondansetron and Metoclopramide are FDA-approved for preventing nausea and vomiting-related chemotherapy and radiation therapy.
• Both are available as oral tablets, oral liquids, and injectable forms.
• Both are generally well-tolerated and have few side effects.
• They are well tolerated and associated with minimum side effects.

What is the Difference Between Ondansetron and Metoclopramide?

Ondansetron and Metoclopramide are medications primarily prescribed to treat nausea and vomiting associated with cancer chemotherapy treatment. Although they are indicated for similar conditions, there is a distinct difference between Ondansetron and Metoclopramide. Ondansetron is a selective serotonin receptor antagonist, while Metoclopramide is a dopamine receptor antagonist and a prokinetic agent. Ondansetron is generally well-tolerated and has fewer side effects compared to Metoclopramide. In addition, Ondansetron is more expensive than Metoclopramide. Ondansetron is a carbazole derivative with a substituted imidazole ring, while Metoclopramide is an amino-benzamide derivative with an ethyl-amino side chain and a methoxy group. Ondansetron is available as Zofran, Zuplenz, while Metoclopramide is available as Gimoti, Reglan.

Below is a summary of the difference between Ondansetron and Metoclopramide in tabular form for side-by-side comparison.

Summary – Ondansetron vs Metoclopramide

Ondansetron and Metoclopramide are commonly prescribed to treat chemotherapy-related nausea and vomiting. However, there is a distinct difference between Ondansetron and Metoclopramide. Ondansetron is a selective serotonin receptor antagonist, while Metoclopramide is a dopamine receptor antagonist. The most common side effects of Ondansetron include headache, constipation, and dizziness. In contrast, Metoclopramide has more side effects than Ondansetron, including drowsiness, dry mouth, anxiety, and restlessness. Comparatively, Ondansetron is more expensive than Metoclopramide. Ondansetron is available as Zofran, Zuplenz, while Metoclopramide is available as Gimoti, Reglan. Although both Ondansetron and Metoclopramide are effective in managing nausea and vomiting, the best medication for the individual conditions may depend on their need and preference.

Reference:

1. Roila, Fausto, and Albano Del Favero. “Ondansetron Clinical Pharmacokinetics.” Clinical Pharmacokinetics, vol. 29, no. 2, 1995, pp. 95–109.
2. “Metoclopramide – Uses, Interactions, Mechanism of Action.” DrugBank Online.

Image Courtesy:

1. “Ondansetron Skeletal” By Fvasconcellos 00:15, 14 April 2007 (UTC) – Own work (Public Domain) via Commons Wikimedia
2. “Metoclopramide” By Harbin – Own work (Public Domain) via Commons Wikimedia