Opioids

Question 1

Describe the mechanism of action of morphine.

Answer 1

1) Spinal effect: inhibits ascending pathway by activating MOR in dorsal horn to inhibit neurotransmitter release from pain fiber.
2) Supra-spinal effect: activates descending pain pathway by activating MOR in PAG (periaqueductal grey)

So basically it stimulates the PAG which is the body’s way of signaling for endogenous opioid release to stop feeling pain while also activating opioid receptors in the C-fibers in the periphery.

Question 2

Describe the general effects of opioid analgesia.

Answer 2

They increase the pain threshold and tolerance, and are selective for analgesia so they have little to no effect on other somatosensory modalities (e.g. touch, temp, proprioception). It is better against slow pain, and not very effective against neuropathic pain.

Question 3

What drugs share the same mechanism as morphine?

Answer 3

Meperidine, methadone, fentanyl, codeine, oxycodone, and hydrocodone. AKA high, medium, and low efficacy agonists all work by same mechanism but potency varies

Question 4

Name the low-medium efficacy agonists.

Answer 4

Codeine, oxycodone, hydrocodone.

Question 5

Which opioid causes tachycardia?

Answer 5

Meperidine.

*meeeeeep (sound of an unhappy heart)

Question 6

Why might one prescribe meperidine over morphine?

Answer 6

Even though it is only 10% as potent, it is faster acting and is only used short-term (

Question 7

What are the side effects associated with morphine?

Answer 7

RUSHPNC - resp depression, urinary retention, sedation, hypotension from histamine release, pruritis, nausea, constipation

*Gotta rush to morph so you can fight the bad guys with your power ranger friends

Question 8

What is the first line tx for moderate to severe pain?

Answer 8

Morphine

Question 9

What are the contraindications to morphine?

Answer 9

Things that would be affected by resp depression/constipation –> severe asthma/upper aw obstruction, paralytic ileus

Question 10

What drug interactions are concerning for meperidine?

Answer 10

MAOIs & SSRIs (serotonin syndrome), tramadol, methadone

Question 11

What side effects are associated with meperidine?

Answer 11

In the liver it is metabolized to a toxic metabolite (normeperidine) that causes CNS hyperactivity and convulsions, mydriasis (dilated pupils), anticholinergic effects (tachycardia)

Question 12

What are the clinical uses of methadone?

Answer 12

It is used to treat heroin addiction and is also a good analgesic for severe pain (another first line tx along with morphine)

Question 13

What is the clinical use of fentanyl?

Answer 13

It is first line tx for breakthrough pain. It is also commonly used for post-op and labor analgesia via epidural, and is the primary anesthetic for cardiovascular surgery and patients with poor cardiac fxn.

*When you don’t do anal you end up with babies and a broken heart.

Question 14

Name the high efficacy agonists.

Answer 14

Morphine, meperidine, methadone, and fentanyl

*MMMF - more meth fun meeeeep, so high.

Question 15

Discuss the side effects of low-medium efficacy agonists.

Answer 15

They are usually combined with acetaminophen to improve analgesia by incorporating another mechanism, so the acetaminophen risks liver toxicity. Otherwise side effects mirror morphine (histamine release –> pruritis, hypotension, and bronchospasm).

*Remember these are codeine, hydrocodone, and oxycodone (CHO, you don’t work so great)

Question 16

Discuss the mechanism of action of pentazocine.

Answer 16

It is a mixed agonist/antagonist drug so it is a kappa agonist (where analgesia comes from) and partial mu antagonist

*If you’re the king you live in the penthouse and the rest of mu live in the dungeons (k for kappa)

Question 17

Discuss the side effects of pentazocine.

Answer 17

Because it is a partial mu antagonist it can precipitate withdrawal in patients on mu opioid receptor full-agonists. Also has some unique psychomimetic side effects (dysphoria, hallucinations). Don’t inject, causes necrosis at injection site.

*Watching my bank account waste away paying for a penthouse would make me crazy

Question 18

Describe the mechanism of action of buprenorphine.

Answer 18

It is a partial mu agonist and kappa antagonist.

*Bu rhymes with mu

Question 19

What is the clinical application for buprenorphine?

Answer 19

It treats mild-moderate pain and is widely used to treat opioid dependence (often combined w/ naloxone).

Question 20

Describe the mechanism of action and clinical application of naloxone.

Answer 20

It is a mu opioid receptor antagonist used to treat opioid overdose!

Question 21

What are the side effects associated with naloxone?

Answer 21

It can cause pruritis, nausea, hyper/hypotension, pulmonary edema, and hepatotoxicity

Question 22

Describe the mechanism of action and clinical use of dextromethorphan.

Answer 22

It is an opioid that acts on DM receptors, and also acts as an NMDA receptor antagonist (glutamate receptor antagonist) and is used as an antitussive.

*Robitussin DM

Question 23

What should be used to manage mild pain?

Answer 23

ASA (aspirin), APAP (acetaminophen), and NSAIDS

Question 24

What should be used to manage moderate pain?

Answer 24

Drugs used for mild pain plus an oral opioid (aka the low-medium efficacy ones)

Question 25

What drugs should you use to manage severe pain?

Answer 25

High-efficacy opioids

Question 26

What are the primary uses of opioids?

Answer 26

Analgesia, antitussive (as long as there aren’t tons of secretions), and antidiarrheal (but can cause constipation).