Medicines for Post-Operative Nausea and Vomiting

Question 1

What medicine given prior to anaesthetic induction reduces the risk of post-operative nausea and vomiting?

Answer 1

Dexamethasone (4 to 8 mg) prior to induction of anaesthesia is effective in the prevention of PONV. This dose is also effective against late vomiting up to 24 hours postoperatively. Adverse effects associated with corticosteroid administration have not been reported with a single dose of dexamethasone.

Question 2

What are some adverse effects of opioid analgesics?

Answer 2

Sedation, itch, nausea, vomiting, gut motility reduction (constipation) and urinary retention. Adverse events are dose related.

Question 3

Why is codeine not effective in some people?

Answer 3

Codeine is metabolized by CYP 2D6 to morphine and therefore about 10% of the population will not be able to make the conversion and get effective analgesia, as they are CYP 2D6 deficient.

Question 4

Why is use of pethidine (an opioid analgesic) usually discouraged?

Answer 4

1. Short-acting
2. Risk of accumulation of toxic metabolite (nor-pethidine) which can cause seizures
3. Abuse potential is high

Question 5

Why should the combination of tramadol and pethidine be avoided?

Answer 5

Risk of serotonin syndrome

Question 6

Does 10mg metoclopramide IV intra-operatively prevent post-operative nausea and vomiting?

Answer 6

No

Question 7

What is the dosing interval for dexamethasone

Answer 7

Dexamethasone should only be administered 8 hours after the last dose for the treatment of PONV

Question 8

What is the dosing interval for 5-HT3 antagonists (e.g. ondansetron)

Answer 8

Ondansetron and other 5-HT3 antagonists should only be administered 6 hours after the last dose for the treatment of PONV