Session 9.1 - Opioids

Question 1

Morphine

Answer 1

Drug Class: Strong Agonist

Mechanism of Action: Targets μ receptors

Common Indicators: Analgesia, Palliative

ADRs: Resp Depression (reduces responsiveness of medullary resp centre to CO2, leading to CO2 toxicity), Emesis, Constipation

Important drug-drug rxns: none

Question 2

Fentanyl

Answer 2

Drug Class: Strong Agonist

Mechanism of Action:
μ-receptors Affinity: Fentanyl > Morphine
Potency: Fentanyl > Morphine

Common Indicators: Analgesia, Anaesthetic, Palliative

ADRs: Resp Depression, Constipation, Emesis

Important drug-drug rxns:

Question 3

Codeine

Answer 3

Drug Class: Moderate Agonist

Mechanism of Action:
1/10th potency than Morphine
Codeine -> Morphine via CYP2D6,
CYP2D6 variable expression (Polymorphism),

Common Indicators: Mild Analgesia, Cough depressant

ADRs: Resp Depression, Constipation

Important drug-drug rxns: CYP2D6 is inhibited by Fluoxetine (SSRI)

Question 4

Buprenorphine

Answer 4

Drug Class: Mixed Agonist-Antagonist

Mechanism of Action: (Compared to Morphine:)

• High affinity for μ-opioid receptors, Low Kd
• Lower Emax as its a partial agonist

Common Indicators: Moderate-sever Analgesia,
Opioid addiction treatment (due to agonist-antagonist properties)

ADRs: Resp Depression, Low BP, Nausea, Dizziness

Important drug-drug rxns: none

Question 5

Naloxone

Answer 5

Drug Class: Opioid Antagonist

Mechanism of Action:

• Competitive agonist of opioid
• Affinity μ>δ>κ
• Greater affinity than morphine, less affinity than Buprenorphine

Common Indicators: Reverse opioid effect

ADRs: Severe withdrawal effects in opioid addicts

Important drug-drug rxns: none