Opioid Pharmacology

Question 1

Oral bioavailability definition

Answer 1

The percentage of the total drug dose administered that reaches the circulation. Taking into consideration how much is absorbed by the mouth.

Question 2

What is first pass metabolism by the liver

Answer 2

50% of oral (enteral) morphine is metabolised by first pass metabolism.
Therefore, if 10mg of morphine is given orally the equivalent is 5mg SC, IV, IM

Question 3

Potency definition

Answer 3

Whether a drug is ‘strong’ or ‘weak’ relates to how well the drug binds to the receptors the binding affinity

Question 4

Efficacy defintion

Answer 4

The concept of full or partial agonists

Question 5

Tolerance definition

Answer 5

Down regulation of the receptors with prolonged use. Need higher dose to achieve the same effect

Question 6

Dependence definition

Answer 6

Phycological - craving, euphoria

Question 7

Opioid withdrawal

Answer 7

Starts within 24 hours, lasts about 72 hours

Question 7

Why do you get side effects with opioid use and what are they

Answer 7

Opioid receptors exist outside the pain system e.g., digestive tract, respiratory control centre
Side effects:
Respiratory distress,
Sedation,
Nausea and vomiting,
Constipation,
Itching,
Immune suppression,
Endocrine effects

Question 8

How to treat opioid induced respiratory depression

Answer 8

Naloxone - 1ml in 10ml saline
Titrate to effect

Question 9

How does codeine work?

Answer 9

Pro-drug = needs to be metabolised by cytochrome CYP2D6 to morphine to work