Choose the drug by the receptor pathway driving the nausea
Mnemonic
Match the receptor to the cause:
| Cause | Mechanism | Drug |
|---|---|---|
| Chemotherapy, radiotherapy | 5-HT3 from the gut | Ondansetron |
| Opioids, metabolic, drugs | D2 at the chemoreceptor trigger zone | Haloperidol, metoclopramide |
| Gastric stasis | Prokinetic needed | Metoclopramide, domperidone |
| Motion, vestibular | H1 and muscarinic | Cyclizine, hyoscine, prochlorperazine |
| Raised intracranial pressure | Oedema | Dexamethasone, cyclizine |
| Anticipatory | Anxiety | Lorazepam |
“Where is the vomiting coming from?” determines the drug, and that question is answered by the history rather than by trying agents in sequence.
Cautions worth carrying: metoclopramide causes extrapyramidal reactions, especially in the young, and is avoided in bowel obstruction; ondansetron constipates and prolongs the QT; cyclizine can cause tachycardia and is disliked in heart failure; prochlorperazine and metoclopramide are best avoided in Parkinson’s disease, where domperidone is preferred because it does not cross the blood brain barrier.
Expansion
| Cause | Pathway | Drug of choice |
|---|---|---|
| Chemotherapy, postoperative | 5-HT3 from gut enterochromaffin cells | Ondansetron, plus dexamethasone and aprepitant |
| Gastric stasis, ileus | Gut motility | Metoclopramide, domperidone (prokinetic) |
| Metabolic (uraemia, hypercalcaemia, opioids) | Chemoreceptor trigger zone, D2 | Haloperidol, levomepromazine |
| Vestibular, motion | H1 and muscarinic | Cyclizine, hyoscine, prochlorperazine |
| Raised intracranial pressure | Central | Dexamethasone, cyclizine |
| Anxiety, anticipatory | Cortical | Benzodiazepine |
Cautions worth knowing
- Metoclopramide causes extrapyramidal effects, particularly acute dystonia in young women, and is contraindicated in Parkinson disease and in bowel obstruction. Use is limited to 5 days
- Domperidone does not cross the blood-brain barrier so is preferred in Parkinson disease, but prolongs the QT interval
- Ondansetron causes constipation and QT prolongation
- Cyclizine is antimuscarinic and can cause confusion in the elderly
In mechanical bowel obstruction, prokinetics are contraindicated and cyclizine or haloperidol with an antisecretory agent is used instead.