week 14

Question 1

what are the 3 opioid receptor subtypes

Answer 1

mu
kappa
delta
all are G protein coupled

Question 2

mechanism of action of opioids

Answer 2

Primarily mu opioid receptor agonism.

Closure of voltage gated Ca channels on presynatpic nerve terminals = reduce transmitter release.

Open K channels on postsynaptic neurons = hyperpolarisation = inhibit neuron.

Question 3

mechanism of action of moprhine

Answer 3

Binds to μ-opioid receptors (mainly), also κ and δ to a lesser extent

Gi protein-coupled receptor → inhibits adenylyl cyclase

↓ cAMP → ↓ Ca²⁺ influx + ↑ K⁺ efflux

Leads to neuronal hyperpolarisation and reduced neurotransmitter release

Question 4

mechanism of action of methadone

Answer 4

mu opioid receptor agonist.
acts on NMDA receptor antagonist.
blockade of monamine reuptake ( serotonin + norepinephrine)

Question 5

half life of methadone

Answer 5

25-52 hours

Question 6

cardiac risks of methadone

Answer 6

QT prolongation, TdP

Question 7

advantages of fentanyl

Answer 7

Safe in renal failure with less active metabolites.
haemodynamically stable

Question 8

metabolism of oxycodone

Answer 8

Liver – mainly CYP3A4 → noroxycodone (inactive);
minor via CYP2D6 → oxymorphone (active)

Question 9

mechanism of action of buprenorphine

Answer 9

partial mu opioid receptor agonist.
kappa opioid receptor antagonist.

slow dissociation -> long duration.

Question 10

active metabolite of buprenorphine

Answer 10

norbuprenorphine

Question 11

relationship of buprenorphine and naloxone

Answer 11

Buprenorphine is not easily reversed by naloxone due to its high affinity for mu receptors.

However, relatively low risk of respiratory depression

Question 12

class of drug of tramadol

Answer 12

Atypical opioid analgesic.
Dual action; opioid and monamine pathways
weak mu opioid receptor agonist.
Inhibits serotonin and noradrenaline reuptake.

Question 13

mechanism of action of tramadol

Answer 13

mu opioid receptor agonism.
5-HT (serotonin) reuptake inhibition - enhances descending pain inhibition.
NA reuptake inhibition - enhances analgesia via spinal mechanisms.

Question 14

effects of toxicity and overdose with tramadol

Answer 14

Seizures; especially with TCAs, SSRIs.
Serotonin syndrome.
Respiratory depression.

naloxone may reverse respiratory depression but worsen seizures.

Question 15

mechanism of action of naloxone

Answer 15

Opioid antagonist.
Competitive antagonist at opioid receptors.
Displaces opioids from receptors.