Anti-emetic Selection Guide
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Drug Information Cards
Metoclopramide
Dopamine D2 blocker + prokinetic
Onset: 30-60 min
Key side effects: Drowsiness, extrapyramidal symptoms, tardive dyskinesia
Domperidone
Peripheral dopamine D2 blocker
Onset: 45-90 min
Key side effects: Dry mouth, cardiac QT prolongation
Prochlorperazine
Dopamine antagonist (phenothiazine)
Onset: 15-30 min
Key side effects: Sedation, extrapyramidal effects, low blood pressure
Ondansetron
5-HT3 receptor antagonist
Onset: 10-15 min
Key side effects: Constipation, headache, rare QT prolongation
Granisetron
5-HT3 receptor antagonist (long-acting)
Onset: 15-30 min
Key side effects: Constipation, abdominal pain
Key Takeaways
- Metoclopramide works by blocking dopamine receptors and speeding up stomach emptying, making it a go‑to for gastroparesis and post‑surgical nausea.
- Domperidone offers similar dopamine blockade but stays out of the brain, reducing the risk of movement disorders.
- Ondansetron and Granisetron target serotonin (5‑HT3) receptors, excelling in chemotherapy‑induced nausea but not in gastric motility.
- Prochlorperazine is a broad‑spectrum anti‑vomiting drug but carries a higher chance of sedation and extrapyramidal effects.
- Choosing the right drug hinges on the underlying cause, required speed of relief, and the patient’s tolerance for side‑effects.
What is Metoclopramide?
Metoclopramide is a dopamine D2‑receptor antagonist that also enhances acetylcholine release in the gastrointestinal tract, improving gastric emptying and reducing nausea. First approved in the 1960s, it’s widely used for three main purposes: treating nausea/vomiting, managing gastroparesis, and facilitating certain radiographic procedures. In Australia, the Therapeutic Goods Administration (TGA) lists it as a prescription‑only medicine, typically supplied in 5‑mg tablets or injectable form.
Because it crosses the blood‑brain barrier, Metoclopramide can affect the central nervous system. That’s why it carries a black‑box warning for tardive dyskinesia when used beyond two weeks. Short courses (usually 3‑5 days) stay well within safety limits for most patients.
Common Alternatives at a Glance
When doctors talk about “anti‑emetics,” several names surface. Below are the most frequently mentioned substitutes, each with a distinct mechanism.
Domperidone is a peripheral dopamine antagonist that does not readily enter the brain, lowering the risk of movement disorders.
Prochlorperazine is a phenothiazine that blocks dopamine receptors and also has antihistamine properties, often used for severe vomiting.
Ondansetron is a selective 5‑HT3 receptor antagonist, the drug of choice for chemotherapy‑induced nausea and post‑operative nausea.
Granisetron works similarly to Ondansetron but has a longer half‑life, making it useful for multi‑day chemotherapy regimens.
Chemotherapy‑induced nausea is a specific clinical scenario where serotonin release from the gut triggers the vomiting center.
Tardive dyskinesia is a potentially irreversible movement disorder that can appear after prolonged dopamine‑blocking therapy.
Side‑by‑Side Comparison
| Drug | Primary Mechanism | Typical Adult Dose | Onset of Relief | Key Side Effects | Australian TGA Status |
|---|---|---|---|---|---|
| Metoclopramide | Dopamine D2‑blocker + pro‑kinetic | 10mg orally q6h (max 40mg/day) | 30‑60min | Drowsiness, extrapyramidal symptoms, tardive dyskinesia (long‑term) | Prescription‑only |
| Domperidone | Peripheral dopamine D2‑blocker | 10mg orally q8h (max 30mg/day) | 45‑90min | Dry mouth, cardiac QT prolongation (high doses) | Prescription‑only |
| Prochlorperazine | Dopamine antagonist (phenothiazine) | 5‑10mg orally q6‑8h | 15‑30min | Sedation, extrapyramidal effects, low blood pressure | Prescription‑only |
| Ondansetron | 5‑HT3 receptor antagonist | 4‑8mg orally q8h | 10‑15min | Constipation, headache, rare QT prolongation | Prescription‑only |
| Granisetron | 5‑HT3 receptor antagonist (long‑acting) | 1mg IV/IM (single dose) or 3mg transdermal patch | 15‑30min | Constipation, abdominal pain | Prescription‑only |
Choosing the Right Antiemetic: Scenarios that Matter
- Gastroparesis or delayed gastric emptying - Metoclopramide’s pro‑kinetic action makes it the first‑line choice. Domperidone can be substituted if central side effects are a concern, but its peripheral action means a slightly slower gastric effect.
- Short‑term postoperative nausea - Ondansetron or Granisetron work fastest because they block serotonin released during surgery. Metoclopramide is still useful, especially when patients also need gastric motility support.
- Chemotherapy‑induced nausea (CINV) - 5‑HT3 antagonists (Ondansetron, Granisetron) dominate. Adding Metoclopramide may help if nausea persists after the serotonin pathway is blocked.
- Severe vomiting of unknown origin - Prochlorperazine offers broad coverage and rapid onset, but watch for sedation and extrapyramidal risk, especially in the elderly.
- Patients with cardiac risk - Domperidone can prolong QT at high doses; avoid in patients with known arrhythmias. Ondansetron also carries a modest QT warning.
In practice, doctors often start with the drug that best matches the underlying cause, then switch if side‑effects appear or efficacy falls short.
Safety Profile Deep Dive
All anti‑emetics share some overlap in side‑effects, yet the severity and frequency differ.
- Metoclopramide - The biggest red flag is tardive dyskinesia, a movement disorder that can become permanent after weeks of high‑dose use. The risk climbs sharply beyond 2weeks, so most guidelines cap therapy at 5days for nausea and 4weeks for gastroparesis with close monitoring.
- Domperidone - Because it stays outside the brain, central side‑effects are rare. However, it can affect heart rhythm, especially when combined with other QT‑prolonging drugs like macrolide antibiotics.
- Prochlorperazine - Sedation is common, and older adults may develop confusion. Extrapyramidal symptoms (muscle stiffness, tremor) are possible, similar to Metoclopramide but usually less severe.
- Ondansetron & Granisetron - Generally well‑tolerated. The most reported issues are constipation and mild headache. QT prolongation is dose‑dependent, so electrolytes should be checked in high‑risk patients.
Drug interactions matter too. Metoclopramide inhibits CYP2D6, potentially raising levels of antidepressants like fluoxetine. Domperidone is metabolized by CYP3A4, so strong inhibitors (ketoconazole, erythromycin) can increase its plasma concentration.
Practical Tips for Clinicians and Patients
- Always start low, go slow - For Metoclopramide, 5mg before meals can reduce GI upset while still providing benefit.
- Check renal function before prescribing Metoclopramide or Domperidone; dose adjustments are needed in chronic kidney disease.
- Educate patients about early signs of tardive dyskinesia - involuntary facial grimacing, tongue protrusion, or lip smacking - and advise immediate medical review.
- Consider transdermal Granisetron for patients who have difficulty swallowing tablets during chemotherapy cycles.
- In pregnancy, Metoclopramide is Category B (Australia) and often preferred over other dopamine blockers, but avoid high‑dose regimens without obstetric consultation.
Frequently Asked Questions
Can I use Metoclopramide for occasional motion sickness?
Yes, a single 10mg dose taken 30 minutes before travel can help, but avoid daily use because the risk of movement disorders rises with repeated exposure.
Is Domperidone safer for elderly patients?
Generally, yes. Since Domperidone does not cross the blood‑brain barrier, it causes fewer central side effects, making it a better option for seniors who are prone to confusion or falls.
When should I switch from Metoclopramide to a 5‑HT3 antagonist?
If nausea persists after 24‑48hours of Metoclopramide or if the patient develops any extrapyramidal symptoms, a switch to Ondansetron or Granisetron is advised.
Can Metoclopramide interact with antidepressants?
Yes. Metoclopramide inhibits CYP2D6, which can raise levels of SSRIs such as fluoxetine and paroxetine, potentially increasing serotonin syndrome risk. Monitor symptoms and adjust doses if needed.
What monitoring is required for long‑term Metoclopramide therapy?
Baseline neurology assessment, followed by monthly check‑ins for any involuntary movements. Liver and kidney tests every 3‑6months are also recommended.
Overall, Metoclopramide remains a versatile tool in the anti‑emetic arsenal, but its central action demands careful timing and patient selection. Alternatives like Domperidone, Prochlorperazine, Ondansetron, and Granisetron fill specific gaps-whether you need rapid serotonin blockade, a peripheral dopamine effect, or a longer‑acting patch. By matching the drug’s mechanism to the cause of nausea and weighing side‑effect profiles, you can achieve relief with the least hassle.
Andy V
October 3, 2025 AT 23:25First off, the term should be “anti‑emetic” with a hyphen, not “antiemetic”. Also, “dopamine D2‑blocker” needs a hyphen between D2 and blocker for clarity. The table’s dosage column mixes “mg” and “g” inconsistently; stick to milligrams throughout.
Tammie Sinnott
October 8, 2025 AT 16:52When you break down the mechanisms, you’ll notice that metoclopramide’s dual action-dopamine antagonism plus pro‑kinetic acetylcholine release-makes it uniquely suited for gastroparesis, whereas ondansetron’s pure 5‑HT3 blockade shines in chemotherapy‑induced nausea. The onset times listed reflect pharmacokinetics: ondansetron hits within 10‑15 minutes because it’s a direct receptor antagonist, while domperidone lags due to peripheral distribution. If a patient has a cardiac history, you’ll want to avoid domperidone’s QT‑prolonging potential and lean toward a 5‑HT3 agent, ensuring you monitor electrolytes if you still need a dopamine blocker.
Michelle Wigdorovitz
October 13, 2025 AT 10:20From a global health angle, the availability of these drugs varies dramatically-ondansetron is on the WHO essential medicines list, but metoclopramide remains the workhorse in low‑resource settings because it’s cheap and oral. The pro‑kinetic benefit is especially valuable where endoscopic interventions for gastroparesis aren’t feasible. However, clinicians must stay vigilant for extrapyramidal side‑effects, which can be under‑reported in regions without routine neurologic follow‑up.
Arianne Gatchalian
October 18, 2025 AT 03:47I completely agree with the point about resource‑limited environments; the cost factor often dictates the prescription more than the nuanced side‑effect profile. In practice, I’ve seen nurses educate patients to watch for facial grimacing early on-catching tardive dyskinesia before it becomes entrenched can save a lot of distress.
Aly Neumeister
October 22, 2025 AT 21:14Wow- the chart is super helpful, thanks!
Nilesh Barandwal
October 27, 2025 AT 14:42Indeed, the concise layout demystifies a complex pharmacology landscape, allowing clinicians to match mechanism to pathology with confidence.