opioids

Question 1

why is the oral dose of opiods double IM/IV?

Answer 1

because 50% is lost on first pass metabolism

Question 2

outline the mechanism of opioids in the body, including their receptors.

Answer 2

Opioids bind to opioid receptors in the central and peripheral nervous system:

• Mu (μ) receptors:
• analgesia
• euphoria
• respiratory depression.
• Delta (δ) receptors:
• analgesia
• mood regulation.
• Kappa (κ) receptors:
• pain relief
• dysphoria.
• cause depression instead of euphoria
• nociceptin opioid-like receptor

Question 3

outline the common prescribed opioids and what theyre used for.

Answer 3

Used for pain management and other conditions.

Examples:
- Morphine: Severe pain relief.
- Fentanyl: Potent, short-acting analgesic (e.g., surgery, chronic pain).
- Oxycodone: Moderate to severe pain.
- Codeine: Mild to moderate pain, also used as a cough suppressant.
- Methadone: Chronic pain and opioid use disorder (maintenance therapy).

Effects:
Pain relief (analgesia), euphoria, sedation, and respiratory depression.

Question 4

outline the opioid drugs which are commonly misused.

Answer 4

Heroin:converted to morphine in the body.

Fentanyl (illicit)

Question 5

describe the physiology of the existing neurological pain pathway.

Answer 5

• nociceptors found in skin, muscles, joints and internal organs activated
• activated by mechanical, thermal or chemical exposure
• signal travels along afferent nerve fibres (A-delta and C fibres)
• this will travel to the dorsal horn
• up the spinothalamic or spinoreticular tract
• to the somatosensory cortex, limbic system and prefrontal cortex

Question 6

name the agonists and antagonists for Mu opioid receptors.

Answer 6

Agonists:
- Morphine:
- Fentanyl:
- Codeine:
- Methadone:
- Buprenorphine:

Antagonists:
- Naloxone: Reverses opioid overdose by displacing opioids from MOR.
- Naltrexone: Long-acting antagonist, used for opioid and alcohol addiction.

Question 7

name the agonists and antagonists for kappa opioid receptors.

Answer 7

Agonists:
- Pentazocine:
- Nalbuphine: Partial agonist, provides analgesia with less euphoria.

Antagonists:
- Buprenorphine:
- Naloxone/Naltrexone: Also blocks kappa receptors, though primarily used for mu receptor antagonism.

Question 8

name the agonists and antagonists for delta opioid receptors.

Answer 8

Agonists:
- Deltorphins (experimental):
- Enkephalins:

Antagonists:
- No commonly used drugs

Question 9

describe the mechanism of how common side effects arise from opioids.

Answer 9

respiratory depression:
- opioids bind to mu receptors in the respiratory centres in the brainstem
- this inhibits the respiratory drive by reducing the sensitivity of the brainstem to carbon dioxide and supressing rhythmic breathing

nausea and vomitting:
- opioids activate the mu receptors in the area postrema in the medulla
- this triggers nausea and vomitting
- additionally, delayed gastric emptying caused by opioids may contribute to nausea

pinpoint pupils:
- opioids stimulate the parasympathetic nerves in the edinger-westphal nucleus of the oculomotor nerve
- causes constriction of pupils

constiption:
- opioids act on mu receptors in the GI tract, reducing peristalsis and intestinal secretions
- leads to prolongued transit time and hardened stool

sedation:
- opioids depress the reticular activating system in the brainstem which is responsible for wakefullness
- leads to drowsiess, lethargy and impared cognition

pruritus / itching:
- opioids cause the release of histamine from the mast cells in the skin
- activation of central opioid receptors may also play a role in inducing itching

tolerance and dependance:
- chronic opioid use leads to receptor downregulation and desensitisation, reducing efficacy over time
- physiological dependance occurs as the body adapts to the presense of the drug, leading to withdrawal symptoms upon cessation