Antiemetics
Antiemetic drugs can be classified by their mechanism of action:
- Serotonin antagonists
- Ondansetron
- Corticosteroids
- Dexamethasone
Has additional effects on postsurgical pain and fatigue.
- Dexamethasone
- Dopamine antagonists
- Phenothiazines
- Chlorpromazine
- Prochlorperazine
- Butyrophenones
- Droperidol
- Benzamides
- Metoclopramide
- Phenothiazines
- Anticholinergics
- Hyoscine
- Atropine
- Antihistamines
- Cyclizine
- NK1 antagonists
- Aprepitant
- Others
- Benzodiazepines
- Cannabinoids
- Propofol
Comparison of Antiemetic Drugs
| Property | Ondansetron | Droperidol | Metoclopramide | Cyclizine |
|---|---|---|---|---|
| Class | Serotonin antagonist | Benzamide dopamine antagonist | Dopamine antagonist | Piperazine derivative/H1 antagonist |
| Uses | Nausea. Ineffective for vomiting due to motion sickness or dopamine agonism | Antiemetic, sedation, behavioural control | Prokinetic, antiemetic | Antiemetic (including motion sickness and radiation sickness) |
| Presentation | Tablet, wafer, clear solution for injection at 4mg.ml-1 | Clear solution in brown glass, incompatible with thiopentone and methohexital | Clear solution in plastic | 50mg tablets or 50mg.ml-1 light-sensitive solution |
| Route of Administration | PO/SL/IV | IV | IV/PO | PO/IV/IM |
| Dosing | 4-8mg TDS Give on induction for PONV |
IV Give at end of surgery for PONV |
25-50mg IV (note 10mg has no antiemetic properties | 1mg.kg-1 up to 150mg per day |
| Absorption | PO bioavailability 60% | PO bioavailability 30-90% | PO bioavailability 80% | |
| Distribution | 75% protein bound | 90% protein bound, VD 2L.kg-1 | Minimal protein binding, VD ~3L.kg-1 | |
| Metabolism | Hepatic to inactive metabolites. Dose reduction in hepatic impairment. t1/2 3/24. | Extensive hepatic metabolism | Hepatic metabolism | Hepatic to inactive metabolites |
| Elimination | Renal elimination of inactive metabolites | Renal and hepatic of drug and metabolites | Renal of 20% unchanged drug and remainder as metabolites | Renal of metabolites |
| Mechanism of Action | Central and peripheral antagonism of 5-HT3 receptors, reducing input to the vomiting centre | Central D2 blockade and post-synaptic GABA antagonism | Antiemetic activity via central D2 antagonism, prokinetic activity via muscarinic agonism, peripheral D2 antagonism | Competitive H1 antagonist and anticholinergic at M1, M2, M3 receptors |
| CVS | Bradycardia with rapid IV administration, QT prolongation | QT prolongation, hypotension secondary to α antagonism | ↑/↓ HR, ↑/↓ BP | ↑ HR and ↓ BP due to α antagonism |
| CNS | Headache | Sedation (neurolepsis), extrapyramidal symptoms in ~1% | Extrapyramidal symptoms, neuroleptic malignant syndrome | Sedation |
| GIT | Constipation | Antiemetic | Antiemetic, prokinetic | Increased LoS tone |
| Endocrine | Hyperprolactinaemia |
References
- Peck TE, Hill SA. Pharmacology for Anaesthesia and Intensive Care. 4th Ed. Cambridge University Press. 2014.
- Sébastien Pierre, MD, Rachel Whelan. Nausea and Vomiting After Surgery. Contin Educ Anaesth Crit Care Pain 2013; 13 (1): 28-32. doi: 10.1093/bjaceaccp/mks046
- Smith S, Scarth E, Sasada M. Drugs in Anaesthesia and Intensive Care. 4th Ed. Oxford University Press. 2011.