Naloxone

Question 1

What is naloxone

Answer 1

Pure opioid competitive antagonist

Question 2

Which receptors does it effect

Answer 2

All opioid receptors, however affinity is greatest for mu receptors

Question 3

Discuss the pharmaceutical aspects

Answer 3

Presented in 1mL vial containing 400mcg

Also available as a minijet of 400mcg in 2 or 5mLs

Question 4

What is the usual dose

Answer 4

1-4mcg/kg for opioid overdose

Question 5

Discuss the mechanism of action

Answer 5

Naloxone competitively antagonises the opioid receptor, reversing the effects of narcotics by displacing them from the receptor. It has very minimal intrinsic activity

Question 6

What is the onset and duration

Why is this important?

Answer 6

Onset is ~2mins and duration is ~30mins

The duration of naloxone is shorter than morphine and high dose fentanyl - repeated doses will be required

Question 7

Outline the metabolism

Answer 7

Hepatic glucuronidation to naloxone-3-glucuronide

Excreted via the urine

Question 8

What are the major side effects

Answer 8

May precipitate SNS activity causing:
Hypertension, tachycardia and pulmonary oedema
Slow administration risks nausea and vomiting
Crosses placenta - may precipitate acute opioid withdrawal in dependent neonates

Question 9

What is the difference between naloxone and naltrexone

Answer 9

Naltrexone is highly effective orally with a duration of action upto 24hrs