Opioid Analgesics

Question 1

What are some ways of relieving pain?

Answer 1

1. Eliminate cause of pain (anti-inflammatory, chemotherapy (antimicrobials), antiulcer)
2. Prevent transmission (local anesthetics)
3. Affect the way pain is percevied (general anesthetics, opioids)
4. Affect patient’s reaction to pain (anxiolytics, opioids)

Question 2

Body can “self - prescribe” what in situations like bear attack?

Answer 2

Endogenous opioids (endorphins, enkephalins, etc, 5HT, NE)
These inhibit transmission from 1deg to 2deg afferent neurons.

Question 3

What is an opiate?

Answer 3

Drug derived from opium poppy.

-Opium, morphine, codeine

Question 4

What is an opioid?

Answer 4

More generic term; all substances, endogenous and exogenous, that bind opioid receptors

• Endorphins (endogenous)
• Morphine, also an opiate
• Fentanyl, synthetic so not an opiate

Question 5

What is a narcotic?

Answer 5

Originally meant sleep inducing, now legal term encompassing illicit drug use
-Includes opiates, cannabinoids, stimulants, etc.

Question 6

What is the mu receptor known for?

Answer 6

Analgesia, respiratory depression, decreased GI motility, and physical dependence

Question 7

What is the kappa receptor known for?

Answer 7

Analgesia, Sedation, Decreased GI motility

Question 8

How do opioids decrease pain signal and synaptic transmission?

Answer 8

They inhibit VG Ca2+ channels on the presynaptic cell and activate K+ channels on the post synaptic cell. This causes reduced release of glutamate and substance P. They act through G-protein coupled receptors to do this.

Question 9

What other pain medications act on voltage-gated Ca2+ channels?

Answer 9

GABA-pentem which is used in neuropathic pain and through to target MOA channels to impact pain.

Question 10

How does an opioid work through GABA?

Answer 10

• Opioid receptor activation blocks release of GABA from inhibitory interneuron
• GABA inhibits an inhibitory neuron, so when you inhibit GABA with an opioid, you stimulate/allow inhibitory interneuron to work on pain pathway

Question 11

What is the use of Naloxone?

Answer 11

Acute overdose. Antagonist.

• Short duration of action
• Single dose - could relapse after 1-2 hours
• Injection to avoid first pass

Question 12

What is the use of Naltrexone?

Answer 12

Addiction.

• Orally effective
• Small dose, alternate days blocks heroine effects
• Prevent relapse in opioid addiction and alcohol addiction