Opioids Flashcards
Why do we use opioids in animals?
Primarily analgesia for acute pain
Sedation in some patients.
How can we avoid inducing withdrawal in a patient that has received opioids for several days?
Taper over 1-2 days
What are the differences between general anesthesia and analgesia?
Analgesia: loss of sensitivity to pain
Anesthesia: total loss of sensation in part of the body (local block) or the whole body (general anesthesia)
What are the two main opiate receptors targeted clinically?
Mu and Kappa
What are endorphins?
Endogenous opioid ligands
Any endogenous chemical that naturally exhibits pharmacological properties of morphine
What do endorphins do?
Modulate effects on CNS
Mediate analgesia
What is the most potent endogenous opioid peptide mediating analgesia?
Beta endorphin - important in injury and stress, but limited amounts produced
Are opioids more effective for acute or chronic pain?
Acute pain, but role in chronic debilitating pain and cancer pain
Less effective over time
What is opioid induced hyperalgesia?
Increased pain after discontinuation of opioids
What is a full mu agonist?
Max amount of analgesia
Affinity and activity at all receptors
Fentanyl, hydromorphone, methadone, morphine, heroin
What is a partial mu agonist?
Binds partially, provides less analgesia
Buprenorphine
What is a mu agonist-antagonist?
Agonist at kappa receptors, antagonist at mu receptors
Less analgesia, but less side effects
Butorphanol
What is naloxone?
High affinity for mu and kappa receptors
Competitive antagonist
Reverses effects of opioids
Why is affinity of an opioid to the opiate receptor important to know?
Binding ability affects duration of action and drug interaction
Which opioid is difficult to reverse due to high binding affinity?
Buprenorphine
What is pharmacokinetic tolerance?
Induced synthesis of hepatic microsomal enzymes, leading to tolerance
What is pharmacodynamic tolerance?
Cellular adaptations such as changes in the number, affinity, and function of the receptors, leading to tolerance
What is the difference between opioid analgesic potency and efficacy?
Potency: directly related to affinity of drug to receptor
Effect: maximal effect that drug can induce (analgesia)
What is an equi-analgesic dose of hydromorphone (potency 5) to morphine given at a dose of 0.5 mg/kg
Hydro @ 0.1 mg/kg
Is butorphanol (potency 5) more or less effective than morphine for the treatment of severe, acute pain in the dog?
Less effective
Butorphanol activates more kappa receptors so there is a ceiling effect.
What are two reasons that butorphanol is not a great choice to treat severe pain in a dog?
Agonist-antagonist = ceiling effect for analgesia
Short duration of action (0.5-2hrs)
What factors influence the degree of analgesia provided by an opioid?
-Degree of tissue trauma and pain
-acute vs chronic pain
-central vs peripheral sensitization
-degree of fear, anxiety, stress
-route of admin
-dose and interval
-other pain treatments
Are opioids good sedatives in dogs and cats?
Usually not good sedatives on their own in healthy, young animals.
Depends on age, health status, presence of pain
What is dysphoria?
Unpleasant feeling in response to opioid analgesic.
-Disoriented, restless, fear, hiding, vocalizing, painful
What are the effects of opioids on respiratory function?
Respiratory depression
Decrease response in brainstem centers to CO2
How do the resp depressant effects of butorphanol compare to those of morphine?
Torb less resp depression than morphine
Are opioids used for cough suppression?
Yes, directly suppress cough center in medulla. antitussives do not necessarily decr respiration (hydrocodone)
What effect do opioids have on GI motility?
Horses: Slow GI motility: ileus and colic w/ high doses
(butorphanol better)
Other species: constipation
Which opioid is most likely to induce vomiting in dogs and cats?
morphine > hydromorphone
How does tramadol work?
Weak mu opioid agonist
Inhibits NE and serotonin reuptake
What is the advantage of a fentanyl transdermal patch?
Long duration of action (-3 days)
What are the potential consequences of morphine-induced histamine release?
Vasodilation and hypotension
or bronchoconstriction
Do opioids lower the seizure threshold?
No
What is the predominant cardiovascular effect of hydromorphone in the dog?
Bradycardia
How could you completely reverse the effects of hydromorphone?
Naloxone
Common opioids by potency:
- Fentanyl
- Hydromorphone
- Methadone
- Morphine
