Opioid pharmacy

Question 1

What are naturally occurring opioids?

Answer 1

• Morphine
• Codeine (weak)

Question 2

What are routes of administration of opioids?

Answer 2

• Pharmacokinetics
• Oral
• Bioavailability
• First pass metabolism by the liver
  
  • 50% of oral (enteral) morphine
    is metabolised by first pass
    metabolism
  • Halve the dose if giving it s/c
    (subcutaneously), IM, IV
    (parenterally) etc.

Question 3

What will be the fastest out of IM, subcutaneous and IV administration?

Answer 3

1. IV
2. IM
3. Subcutaneous

Question 4

What is the current legislation for Controlled Drugs (CDs)?

Answer 4

Misuse of Drugs Act 1971

Question 5

What class drugs are opioids?

Answer 5

Class A

Question 6

What are practical issues surrounding opioids?

Answer 6

• Secure storage
• CD books - two signatures needed

Question 7

Describe the pharmacodynamics of opioids

Answer 7

• opioid drugs simply use the existing pain modulation system
• Natural endorphins (endogenous morphine) and enkephalins
• G protein coupled receptors - act via second messengers
• Inhibit the release of pain transmitters at spinal cord and midbrain - and modulate pain perception in higher centres - euphoria - changes the emotional perception of pain

Question 8

How do opioids work?

Answer 8

• Descending inhibition of pain
• Part of the fight or flight response
• Never designed for sustained activation
• Sustained activation leads to tolerance and addiction

Question 9

What is potency?

Answer 9

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

Question 10

What if efficacy?

Answer 10

The concept of full or partial agonists

Question 11

What is tolerance?

Answer 11

• Down regulation of the receptors with prolonged use
• Need higher doses to achieve the same effect

Question 12

What is dependance?

Answer 12

• Psychological - craving, euphoria

Question 13

Describe opioid withdrawal

Answer 13

Starts within 24 hours, lasts about 72 hours

Question 14

What do you do in opioid induced respiratory depression?

Answer 14

• Call for help
• ABC
• Naloxone
  
  • 400µg per ml
• IV is fastest route
• Titrate to effect - don’t have to give it all once
  
  • Titrate to effect - dilute 1ml in 10ml saline
• One ampoule of a drug is usually about the right adult dose - if you think you need to open more than one - check with a colleague first
• Short half-life of naloxone - beware drug addict overdoses in A&E

Question 15

Describe opioid use in chronic non-cancer pain

Answer 15

Opioids for non-cancer pain start to lose effectiveness fairly quickly (within weeks)

Question 16

What is codeine?

Answer 16

Codeine is a prodrug - it needs to be metabolised by cytochrome CYP2D6 to morphine to work

Question 17

What are the side affects of opioids?

Answer 17

● Opioid receptors exist outside the pain system e.g. digestive tract, respiratory control centre
● We can sometimes deliver opioids epidurally, but for the most part we have to give them systemically
● Respiratory depression
● Sedation
● Nausea and vomiting
● Constipation
● Itching
● Immune suppression
● Endocrine effects

Question 18

What is morphine metabolised to?

Answer 18

morphine 6 glucuronide which is more potent than morphine and is renally excreted
- With normal renal function this is cleared quickly

Question 19

What could be the consequences of opioids in someone with renal failure?

Answer 19

• In renal failure morphine 6 glucuronide will build up and may cause respiratory depression
• Be careful in patients with < 30% renal function (creatinine clearance < 30)

Question 20

What should you do with patients with renal impairment?

Answer 20

• Reduce dose and timing interval
• It will be dangerous to use morphine - use oxycodone instead