Opioids

Question 1

what do opioids do for level of wakeness and pain

Answer 1

General anesthetics produce unconsciousness but do not inhibit pain signal generation or propagation

Question 2

why do patients not feel mildly painful surgical manipulations

Answer 2

Patients do not feel mildly painful surgical manipulations (e.g., a skin incision) simply because the small numbers of pain signals, which are transmitted to the Reticular Activating System (RAS) in the medulla, are insufficient to awaken the patient

Question 3

how do we prevent the RAS from being stimulated to the point that an anesthetized patient wakes up?

Answer 3

We can prevent this by administering an analgesic beforehand to inhibit pain signal generation

Question 4

is it safe to administer analgesic before anesthetic? why?

Answer 4

This is safer than trying to maintain unconsciousness using higher doses of general anesthetic (which inhibits respiration & CVS function in a dose dependent manner)

Question 5

four things opioid drugs are used for

Answer 5

-analgesia; management of moderate to severe pain
-sedation
-cough suppressant (antitussive)
-treatment of diarrhea (constipation is a major side effect)

Question 6

what three opioid receptor families mediate analgesia

Answer 6

mu (MOR)
delta (DOR)
kappa (KOR)

Question 7

what one of the opioid receptor families produces dysphoria

Answer 7

sigma

Question 8

what is the mechanism of opioid receptors

Answer 8

Opioids stimulate opioid receptors in pain pathways

K+ channels open which causes hyperpolarization and then inhibition of APs

also inhibition of calcium entry which inhibits NT release

Question 9

main effect of MOR stimulation, and others

Answer 9

analgesia; full stimulation causes intense analgesia effects

-euphoria
-miosis or mydriasis
-respiratory depression

Question 10

main effect of KOR stimulation, and others

Answer 10

analgesia; moderate effect, and primarily visceral

-negligable respiratory depressive effects

Question 11

what opioid receptor mediated respiratory depression

Answer 11

Mu receptor

Question 12

difference between full vs partial agonists

Answer 12

full = opioid maximally stimulates opioid receptor

partially = opioid weakly stimulates opioid receptor

Question 13

what makes a mixed agonist/antagonist

Answer 13

some opioids are agonists at some opioid receptors and antagonists at others

Question 14

what type of agonist is fentanyl and what effect does it have

Answer 14

Fentanyl is a full mu agonist = produces an intense analgesic
effect via MOR

Question 15

what type of agonist is butorphenol and what effect does it have

Answer 15

Butorphanol is a kappa agonist
with mild to moderate analgesic
effect

It also very weakly stimulates Mu
receptors, acting as a competitive
antagonist to full Mu agonists

Question 16

what is the analgesic effect of butorphenol and fentanyl combined

Answer 16

weaker analgesia than with fentanyl alone

Question 17

primary effect of

Question 18

what drugs have a mu receptor and what are their interactions

Answer 18

codeine, morphine, hydromorphone, meperidine, fentanyl (all agonists)

buprenorphine and butorphenol (partial agonist)

Question 19

what drugs have a kappa receptor and what are their interactions

Answer 19

buprenorphine and butorphenol (full agonists

Question 20

what drugs have analgesia as their primary effect

Answer 20

codeine, morphine, hydromorphone, meperidine, fentanyl, buprenorphine and butorphenol

Question 21

what drug is good to use for cough suppression

Answer 21

butorphenol

Question 22

what drug is good to use for constipation

Answer 22

loperamide

Question 23

what drug is good to use for emesis in dogs

Answer 23

apomorphine

Question 24

what is the relative duration of analgesia for buprenorphine

Answer 24

4-8 hours

Question 25

what is the relative duration of analgesia for hydromorphone

Answer 25

3-6 hours

Question 26

what is the analgesic potentcy of fentanyl relative to morphine

Answer 26

100x

Question 27

how are opioids normally administered and why

Answer 27

Phase I & Phase II metabolism with high first-pass effect = most opioids are therefore administered parenterally

Question 28

do dogs convert codeine into morphine

Answer 28

only at low or negligable amounts. not nearly the same as humans do

Question 29

what can high doses of morphine cause?

Answer 29

excitement -sham rage (cats) -typically not seen with hydromorphone

Question 30

physiological effects of full Mu agonists on the CNS

Answer 30

-3-6 hours of sedation/analgesia -sedation is most likely in dogs, excitement is most likely in other species

Question 31

physiological effects of full Mu agonists on the cardiovascular system

Answer 31

Usually little effect on CVS at the dosages normally administered

Question 32

what can morphine trigger

Answer 32

may trigger histamine release = vasodilation = hypotension

Question 33

physiological effects of full Mu agonists on the respiratory system

Answer 33

* Dose-dependent depression * More intense effect when combined with a general anesthetic * Death from overdose is due to respiratory arrest – a Mu effect * Use naloxone to reverse * Opioids suppress the cough reflex

Question 34

physiological effects of full Mu agonists on the gastrointestinal system

Answer 34

* Increase segmentation but reduce propulsion in large bowel = stool becomes dehydrated = constipation * Bile duct sphincter constriction = increase in gall bladder pressure = biliary colic * Nausea & vomiting (chemoreceptor trigger zone MOR stimulation)

Question 35

what do opioids do to the bladder

Answer 35

Urinary bladder sphincter tone increased & detrusor muscle tone increased = urgency to urinate but difficult

Question 36

what do we specifically need to worry about related to bladders and uterus when giving opioids

Answer 36

* Dogs may have difficulty urinating post-op * Problems with blocked cats * Opioids also slow uterine contractions, inhibit birth reflexes, depress neonatal resp.

Question 37

most common way fentanyl is administered

Answer 37

transfermal patch

Question 38

what is fentanyl used for

Answer 38

* For profound pain relief in small animals * Also commonly used as an analgesic and sedative prior to induction

Question 39

do you need a reversal agent for etorphine? what is its potency compared to morphine

Answer 39

yes, its required for recovery 4000x more potent than morphine

Question 40

what is butorphenol used for

Answer 40

Used for mild/moderate pain; ineffective for severe pain

Question 41

what type of agonist is butorphenol

Answer 41

kappa agonist and mu antagonist

Question 42

main advantage of buprenorphine

Answer 42

-Main advantage is for home (oral transmucosal) administration for animals with chronic pain (long duration)

Question 43

what is apomorphine used for

Answer 43

used to cause dogs to vomit

Question 44

can naloxone sotp vomit reflex

Answer 44

no

Question 45

what is an alternative to apomorphine

Answer 45

ropinirole

Question 46

what is a common anti-diarrheal in vet med

Answer 46

loperamide (imodium)

Question 47

what is the main opioid antagonist and how does it work

Answer 47

naloxone bind and block mu opioid receptors through competitive inhibition