Opioids

Question 1

Opium

Answer 1

Natural extract of the poppy papaver somniferum. It contains morphine and other related compounds

Question 2

Opioid

Answer 2

Any substance (natural or synthetic) that produces morphine like effects which are blocked by a morphine antagonist

Question 3

Opiate

Answer 3

Normally occurring opioid

Question 4

What is the ceiling effect?

Answer 4

Weak opioids: escalation of the dose typically causes side effects without improving analgesia

Question 5

Strong opioids

Answer 5

• Morphine
• Oxycodone
• Diamorphine
• Fentanyl
• Pethidine
• Remifentanil
• Methadone

Question 6

Weak opioids

Answer 6

• Codeine
• Dihydrocodeine
• loperamide (Imodium)

Question 7

What is special about loperamide?

Answer 7

It is not an alagesic but is an agonist of the opioid receptors in the myenteric plexus so stops diarrhoea

Question 8

Tramadol

Answer 8

Developed as an antidepressant but found to have analgesic actions
Pro convulsive drug so avoid in epilepsy

Question 9

Naloxone

Answer 9

Primary antagonist of opioids

Question 10

What administration is most common in post op care?

Answer 10

• IV (patient controlled)

* Intra muscular (avoid the sciatic nerve)

Question 11

What administration is most common in palliative care (or for weak opioids)

Answer 11

• Oral

* Transdermal patch

Question 12

What administration is most common for labour or big operations?

Answer 12

Catheter in the extradural space

Question 13

What administration is most common for trauma

Answer 13

‘lollipop’ or lozenge

Question 14

Explain oral bioavailability of opioids

Answer 14

• First pass metabolism
• Opioids are weak bases
• Unionised form is more diffusible
• Stomach is very acidic so is ionised
• Alkaline environment pushes drug into ionised states and it passes into the portal circulation and travels to the liver

Question 15

What are the opioid receptors?

Answer 15

• Mu opioid peptide receptor (MOP) - majority acts here
• Kappa
• Delta
• Nociception

Question 16

Where are the mu opioid receptors located?

Answer 16

Throughout the NS but especially at sites to do with pain: PAG; dorsal horn, thalamus, cortex, primary afferents

Question 17

What are the endogenous opioids

Answer 17

• Enkephalins
• Endorphins
• Dynorphins

Question 18

Describe the opioid receptors’ structure

Answer 18

• Protein
• Serpantine formation
• 7 transmembrane proteins coupled to G proteins

Question 19

Describe the mechanism of opioid receptors

Answer 19

• closure of voltage sensitive calcium channels
• Opening of potassium channels: potassium moves from inside the cell to outside
• This hyper polarises the cell
• Inhibition of adenylate cyclase leading to reduced neurotransmitter release

Question 20

What are the actions of opioids?

Answer 20

• Analgeisa
• Sedation
• Euphoria
• depresses respiration, antitussive effect
• histamine release
• Bradycardia
• Peripheral vasodilation
• Nausea, constipation
• Urticaria and itch
• Urinary retention
• Immune suppression
• Decreased ACTH, decreased prolactin, increased ADH

Question 21

Describe the metabolism of opioids

Answer 21

• Mostly by cytochrome in the liver

* Many opioids have active metabolites that are excreted by the kidneys in the urine

Question 22

Why should you be careful using opioids in those with renal impairment?

Answer 22

Active metabolites can build up

Question 23

Cautions in extremes of age

Answer 23

• Neonates: liver enzyme sub optimal

* Elderly: smaller volume of distribution

Question 24

What is an antagonist?

Answer 24

A drug with a high affinity for the receptor but no intrinsic activity

Question 25

What is naloxone’s half life

Answer 25

Approx 45 minutes

Question 26

Methadone

Answer 26

Used to manage addiction problems in the community
• Dries mouth
• Long half life
• Crave sweet foods
• Low first pass metabolism so high oral bioavailability
• Less sedating