Opioid drugs

Question 1

Morphine features

Answer 1

Strong opioid receptor agonist (complete activation of μ receptor), analgesic and causes some euphoria

Can be given PO (although gut absorption is erratic), IV, IM, SC, PR

Has significant first pass effect (40% bioavailability), lipophilic so enters all tissues including foetal, struggles to cross blood/brain barrier so not very effective with CNS pain

Eliminated renally so can cause opioid toxicity in patients with AKIs

Question 2

morphine adverse effects

Answer 2

Adverse effects:

• Respiratory Depression
• Vomiting, constipation
• CVS effects
• Miosis
• Histamine release- caution in asthmatics

Question 3

fentanyl features

Answer 3

Strong opioid (μ) agonist; higher affinity, more potent and greater bioavailability (80-100%) than morphine, used as an analgesic and anaesthetic

Highly lipophilic and protein bound so can address CNS pain

Metabolised by CYP 3A4, has a short half life of 6 minutes and renally excreted (but less reliant on the kidney than morphine so has less dangerous in AKI patients)

Question 4

fentanyl adverse effects

Answer 4

• Respiratory Depression
• Constipation
• Vomiting

Question 5

codeine features

Answer 5

Moderate opioid agonist, gets converted into morphine by CYP 2D6 (has variable expression)

Can be given either as PO or SC, excreted via glucuronidation of morphine/renal excretion

Used for mild-moderate analgesia and as a cough depressant

Question 6

codeine adverse effects

Answer 6

• constipation

- respiratory distress (worse in children)

Question 7

buprenorphine features

Answer 7

Mixed agonist-antagonist, has a very high affinity for μ receptors but low Kd and Emax, acts as an antagonist at K receptors

Can be given transdermal, buccal, sublingual, very lipophilic, metabolised by CYP 3A4, excreted via bile so safe for patients with renal impairment, has long half life (37 hrs) so given via patches

Used for moderate to severe analgesia as well as an opioid addiction treatment

Question 8

buprenorphine adverse effects

Answer 8

• Respiratory depression
• Low BP
• Nausea
• Dizziness

Question 9

naloxone features

Answer 9

Opioid receptor antagonist, has greater affinity than morphine but less than buprenorphine (so can displace morphine but not buprenorphine) so used as a competitive antagonist

Can be given IV, IM, intranasal, PO, very low bioavailability cos high first pass effect, rapid distribution cos lipophilic, renally excreted

Has short half life so needs to be given as a slow infusion so that it has enough time for morphine to break down