Pain Management In Small Animals

Question 1

What are 3 main opioid receptors types and their primary effects?

Answer 1

Mu-analgesia, euphoria, respiratory depression, constipation
Kappa-spinal analgesia , dysphoria, diuresis
Delta-analgesia, CV depression

Question 2

How do opioid inhibit pain?

Answer 2

Activate Gi/o -coupled receptors - inhibit neurotransmission in brain/spinal cord

Question 3

Compare morphine and fentanyl in dogs

Answer 3

1.Potency
Morphine -moderate , fentanyl-high
2.onset
Morphine -slow , low bioavailability
Fentanyl -rapid , lipid soluble
3.duration
Morphine 4-6hr , fentanyl 30-60min
4.clinical use
Morphine -acute pain, premedication
Fentanyl-anesthesia adjunct , chronic pain (patches )

Question 4

Why is tramadol only partially reveresed by Naloxone ?

Answer 4

Tramadol’s active metabolite (O-desmethyltramadol) binds mu receptors 20x more strongly. Naloxone has weaker displacement

Question 5

How does buprenorphine work

Answer 5

1.Partial mu agonist (high affinity , low efficacy ) —longer duration (up to 8hrs)
2. K-antagonist—less dysphoria
3. Harder to reverse (has higher receptor binding so Naloxone resistant)

Question 6

What is nalbuphine’s clinical use?

Answer 6

Mild -moderate pain, topical for corneal ulcers (1% solution 4-6x /day)

Question 7

When is Naloxone used?

Answer 7

To reverse respiratory depression from mu agonist ie morphine overdose
Onset : 1-2 min ( IV) lasts 45-90 minutes
Caution also reverses analgesia — may cause pain induced tachycardia

Question 8

How does naltrexone differ from Naloxone?

Answer 8

Longer acting t1/2=4 hours in humans
Used for behavioral issues in dogs ( compulsive licking)
Used for reversing carfentanil in wildlife

Question 9

List 3 species specific opioid side effects

Answer 9

Dogs- panting (thermoregulatory), bradycardia ( vagal stimulation)
Cats -hyperexcitability (high dose mu agonist)
All-constipation ( mu/kappa mediated GI motility inhibition)

Question 10

Why avoid opioids in head trauma?

Answer 10

Increases CO2 , to lead to cerebral vasodilation which worsens hemorrhage /edema

Question 11

Which opiod is best for chronic pain in cats ?

Answer 11

Fentanyl patches ( analgesia in 7-24 hours lasts 72 hours)

Question 12

How is oxymorphone dosed in cats ?

Answer 12

Low dose + tranquilizer ( eg. 0.05mg/kg IM)

Question 13

Give the location for the 3 opiod receptors

Answer 13

1. Mu-brain and laminae 1, 2 of dorsal horn of spinal cord
2. Kappa -cerebral cortex, spinal cord other hypothalamus
3. Delta -limbic system, cerebral cortex and spinal cord