The Opioid Analgesics

Question 1

Nomenclature

Answer 1

Opiod: General name for the class
Includes all drugs that act on opioid receptors
OPIATE
Refers specifically to naturally occurring opioids from the opium poppy
Includes morphine and codeine

Question 2

The opioid receptors

Answer 2

MOP, DOP, and KOP
Most opioid drugs act on the MOP (also called µ or mu) receptors
Located in CNS (brain and spinal cord)
Responsible for the majority of effects and side-effects

Question 3

Major (useful) effects 0f opioids

Answer 3

Centrally-mediated analgesia
Decreased sympathetic response
Sedation
Cough suppression

Question 4

Opioid side effects

Answer 4

Respiratory Distress
Euphoria/ Dysphoria
Prolonged recovery
GIT (Nausea and vomiting/ Constipation
Tolerance, addiction and withdrawal
Pruritis

Question 5

Uses of opioids in anaesthesia

Answer 5

Mainstay of intraoperative analgesia
Mainly fentanyl and morphine
Establishing pre-emptive analgesia
Maintaining intraoperative analgesia (IV boluses or infusion)
Dampening of intubation response (alfentanil)
Additive to LA in neuraxial blockade
Target controlled infusion of remifentanil for intraoperative analgesia
Opioid-based anaesthesia
Cardiovascular instability (trauma, emergencies, cardiac surgery)

Question 6

MORPHINE

general/IV/IM/Orally

Answer 6

General:
The reference opioid drug
Naturally occurring opiate from the opium poppy
Intravenous:
Intraoperative analgesia
Postoperative analgesia in high care setting
Patient controlled analgesia (PCA) pump
IV infusion in ICU and high care
Intramuscular:
Postoperative analgesia in ward
Given 4-6 hourly
Labour analgesia
Orally:
Severe chronic pain
Syrup or tablets
Palliative care cancer pain

Question 7

CODEINE

Answer 7

Weak opiate
Also naturally occurring in opium poppy
Pro-drug—metabolised by liver into morphine
Metabolism varies
Usually oral:
As a combined analgesic (with paracetamol and/or NSAID)
As a standalone oral opioid
Added to cough mixtures for coug suppression
Addictive!

Question 8

The synthetic opioids

Answer 8

Semi-synthetic:
Heroin/Oxycodone
Synthetic
Pethidine
Fentanyl and derivatives (alfentanil/Sufentanil/Remifentanil

Question 9

Fentanyl (Sublimaze ®)

Answer 9

Most commonly used synthetic opioid in anaesthesia:
Onset of action: 10 minutes
Provides intense analgesia for 30-45 minutes (morphine lasts 2-4hrs)
Useful for pre-emptive surgical anaesthesia

Potent:
100 µg = 10 mg of morphine (100 times more potent than morphine)
Significant respiratory depression, can accumulate
Rarely used outside of intraoperative setting

Cardiovascular stability
Can be used as PCA (boluses of 10 µg)
Can be added to local anaesthetic mix in spinal and epidural analgesia

Question 10

Alfentanil (Rapifen ®)

Answer 10

Fentanyl derivate
Rapid onset and offset — lasts 5 minutes
Typical dose: 0.5 to 1 mg IV
Does not readily cross the placenta (Can be used in GA for Caesarean section if needed / Pre-eclampsia)
Useful for blunting intubation response
Emergency “rescue” intraoperative analgesia
Diagnostic use for insufficient analgesia

Question 11

Sufentanil (Sufenta ®)

Answer 11

Similar to Fentanyl in effects
Very potent (typical dose 5–10 µg) i.e. 1000 x more potent than morphine
Few cardiovascular side-effects
Can be given via infusion intraoperatively
(Significant period of good postoperative analgesia
Patient will need high care monitoring post-op)

Question 12

Remifentanil (Ultiva ®)

“MADS”

Answer 12

Unique amongst opioids:
Ultra-short acting
Regardless of dose, metabolised into inactive compounds after 10 minutes
“Context sensitive half-time” of 10 minutes
Spontaneous recovery

MUST BE GIVEN VIA INFUSION= requires infusion pump

Indications:
Sleep apnoea
Morbid obesity
Avoiding postoperaitve respiratory depression
Deep intraoperative analgesia required

Patient will require additional analgesia post-op