Post-Operative Nausea Risk Calculator
Calculate Your PONV Risk Score
The Apfel PONV Risk Score uses four clinical factors to determine your risk of post-operative nausea and vomiting.
When you're recovering from surgery, chemo, or even just taking pain pills, nausea isn't just annoying-it can delay healing, make you dehydrated, or even send you back to the hospital. Medication-induced nausea is one of the most common side effects in hospitals and clinics, affecting up to 30% of surgical patients and over half of those on opioids or chemotherapy. The good news? There are effective antiemetics-but picking the right one isn’t just about what’s on the shelf. It’s about matching the drug to your body, your meds, and your risk level.
How Antiemetics Actually Work
Not all nausea is the same. Your brain has different pathways for triggering vomiting, and each antiemetic blocks a different one. The most common classes you’ll see are:- 5-HT3 antagonists (like ondansetron, granisetron): Block serotonin in the gut and brainstem. Best for chemo and post-op nausea.
- Dopamine antagonists (like droperidol, metoclopramide): Target the brain’s vomiting center. Great for opioid-induced nausea and slow digestion.
- Corticosteroids (like dexamethasone): Reduce inflammation in the gut and brain. Work slowly but boost other drugs.
- Antihistamines and anticholinergics (like promethazine, scopolamine): Mostly useful for motion sickness, less so for drug-induced nausea.
- Opioid antagonists (like naloxone): Rarely used alone, but help when opioids are the direct cause.
For example, if you’re nauseous from morphine after surgery, a dopamine blocker like droperidol works faster and better than ondansetron. But if it’s from chemo, serotonin blockers are the gold standard. Mixing them-like ondansetron plus dexamethasone-often gives the best results.
Which Drugs Are Most Effective?
A 2023 analysis of over 6,600 patients who had cesarean sections showed clear winners:| Drug | Typical Dose | Effectiveness (PONV Prevention) | Cost per Dose | Key Risks |
|---|---|---|---|---|
| Ondansetron (Zofran) | 4-8 mg IV | 65-75% | $1.25 | Headache (32%), dizziness, QT prolongation |
| Droperidol (Inapsine) | 0.625-1.25 mg IV | 67-86% | $0.50 | Low sedation, rare QT risk above 1.25 mg |
| Dexamethasone | 8 mg IV | 20-30% (as add-on) | $0.25 | Delayed effect (4-5 hrs), blood sugar spikes |
| Metoclopramide (Reglan) | 10-50 mg IV | 44% (10 mg), 68% (25 mg) | $0.75 | Akathisia (restlessness), especially in elderly |
| Scopolamine patch | 1.5 mg transdermal | 40-50% | $5-10 | Slow onset (4 hrs), dry mouth, blurry vision |
Here’s what the data says: droperidol at low doses is more effective than ondansetron for post-op nausea, especially in opioid-tolerant patients. And at a fraction of the cost. Ondansetron is popular because it’s safe and works fast-most people feel relief in 15 minutes. But it’s not always the best choice. In fact, studies show combining droperidol and dexamethasone cuts PONV rates nearly in half compared to either drug alone.
Who Should Get What? Risk-Based Selection
You can’t just give everyone the same drug. That’s why doctors use the Apfel PONV Risk Score, based on four simple factors:- Female sex
- Non-smoker
- History of motion sickness or past PONV
- Post-op opioid use
Each factor adds one point. Then:
- 0-1 points: Skip prophylaxis. Give meds only if nausea hits.
- 2 points: Use one drug-either droperidol 0.625 mg or ondansetron 4 mg.
- 3-4 points: Use two drugs together-droperidol + dexamethasone is the top combo.
This approach isn’t theoretical. Hospitals that follow it cut unnecessary antiemetic use by 40% and save $1,000+ per avoided PONV case. One anesthesiologist in Boston reported a 32% drop in rescue meds after switching to this protocol.
Hidden Risks and Common Mistakes
Even safe drugs have traps:- Metoclopramide at 10 mg? Almost useless. At 25 mg, it works-but 30% of elderly patients get severe restlessness (akathisia). Many clinics now use olanzapine 2.5 mg instead for older adults.
- Dexamethasone takes 4-5 hours to kick in. If you give it right before surgery, it’s too late. Give it 1-2 hours pre-op.
- Ondansetron can prolong the QT interval. Avoid it if you have heart rhythm issues or are on other QT-prolonging drugs.
- Scopolamine patches need to be applied 4 hours before surgery. If you forget, they won’t help.
And cost matters. A single dose of netupitant/palonosetron (Akynzeo) costs $350. Generic ondansetron? $1.25. Most patients don’t need the expensive combo unless they’re on highly emetogenic chemo.
What’s New in 2026?
The field is moving fast:- Intranasal ondansetron (Zuplenz) is now approved-great for patients who can’t swallow pills or vomit after surgery.
- NK-1 antagonists like rolapitant are being used more for delayed chemo nausea, with 78% success rates.
- Genetic testing for CYP2D6 enzyme variants is starting to show which patients metabolize ondansetron too fast (and need higher doses) or too slow (and risk side effects).
But the biggest shift? Moving away from "one-size-fits-all" to precision antiemetics. If you’re a 52-year-old woman, non-smoker, with a history of motion sickness, and you’re getting fentanyl after knee surgery-you’re high risk. You don’t need one drug. You need two. And you need them timed right.
Real-World Tips from Clinicians
Practitioners share what works:- "In opioid-tolerant patients, droperidol beats ondansetron every time. No debate." - Anesthesiologist, r/Anesthesiology
- "We switched from metoclopramide to olanzapine for seniors. Akathisia dropped from 8% to under 1%." - Dr. Michael Torres, Medscape
- "Dexamethasone + ondansetron isn’t just better-it’s cheaper than giving three rescue doses of ondansetron." - Dr. Sarah Chen, Mass General
Bottom line: The best antiemetic isn’t the most expensive or the most advertised. It’s the one matched to your body, your meds, and your risk.