Anti-sickness medicines: which one for which cause — and which must never meet?
One reflex, many triggers. Match the drug to the cause, then check its clashes.
Select any card for the reasoning, what to watch for and an exam tip.
Anti-sickness medicines (anti-emetics)
Key points
Anti-sickness drugs are only started once the cause of the vomiting is known — otherwise they can delay diagnosis, particularly in children.
Never give a prokinetic (metoclopramide, domperidone) with a drug that has antimuscarinic action (cyclizine, hyoscine): the antimuscarinic competitively blocks the prokinetic.
Never stack QT-prolongers: ondansetron with domperidone, erythromycin or another 5HT3 antagonist adds arrhythmia risk — and domperidone with ketoconazole or erythromycin is avoided too.
When one anti-sickness drug fails, switch to a different class — two from the same mechanism add side effects, not control.
Aprepitant weakens warfarin (check the INR during and for 14 days after) and the combined pill (add a method).
When to refer
Key takeaway
Match the drug to the cause of the vomiting: prokinetics and antimuscarinics fight each other on the gut, and two QT-prolongers never travel together.
