Find the cause before choosing the antiemetic.
Avoid metoclopramide in bowel obstruction and Parkinson's disease; avoid cyclizine in severe heart failure.
Act now
- 1
IV fluids if dehydrated; review and stop culprit drugs where possible.
Assess
- Causes: drugs (opioids, antibiotics, chemotherapy, digoxin), constipation, obstruction, infection, raised intracranial pressure, vestibular, metabolic (calcium, urea, glucose and ketones), MI, pregnancy.
- Hydration, abdominal examination, bowels, neurological signs.
Investigations
- U&E, calcium, glucose, LFT, amylase; ketones if diabetic; pregnancy test; ECG for QTc before QT-prolonging antiemetics.
- Abdominal imaging if obstruction is suspected.
Manage
- Match drug to cause: gastric stasis → metoclopramide; drug or metabolic → haloperidol or ondansetron; obstruction, vestibular or raised ICP → cyclizine; constipation → laxatives.
- Use one antiemetic first; add a second from a different class if needed.
Escalate when
- Suspected obstruction, haematemesis, raised intracranial pressure, or vomiting with AKI or electrolyte disturbance: senior.
Doses and prescribing
Cyclizine
50 mg oral, IV or IM up to 3 times daily.
Ondansetron
4 mg IV or 8 mg oral, every 8–12 hours as needed. Prolongs QT; constipating.
Metoclopramide
10 mg oral, IV or IM up to 3 times daily, for no more than 5 days.
Haloperidol
0.5–1 mg oral or SC up to twice daily. Check QTc; avoid in Parkinson's disease.
Check the BNF and your local formulary before prescribing.
Written to current guidance · sources checked 14 Nov 2026. We watch NICE for updates weekly.
Sources (1)
Reviewed by Aboodee Alhasso, MPharm MRCPharm IP on 14 Nov 2026
For healthcare professionals, as an aid to clinical judgement — not a substitute for it. Follow your local policy and ask a senior when in doubt.