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When do we use opioids clinically? (4)
premed, induction, maintenance, recovery
What are the effects of opioids? (6)
primary desired effect is analgesia (increase in pain tolerance), WITHOUT effecting senses of touch, vibration, hearing, vision; may also produce dysphoria, euphoria, apprehension, excitement, +/- addiction
What is the mechanism of action of opioids?
reversibly combine with opioid receptors in the CNS (brain- limbic system, periaqueductal grey matter; spinal cord dorsal horn) and in the periphery
What are the types of opioid receptors? (4)
Mu, Kappa, Sigma, Epsilon
What opioid receptors primarily mediate analgesia?
Mu and Kappa
Define opioid agonists.
stimulate all types of opioid receptors
Define opioid agonist-antagonists.
fully or partially stimulate some types of opioid receptors and block activity of others
Define opioid antagonists.
block all activity at all opioid receptors
The potency of opioids is based upon...
the affinity for the opioid receptors.
What are the full opioid agonists? (5)
morphine, meperidine, hydromorphone, oxymorphone, fentanyl
What are the partial agonists? (1)
What are the opioid agonist-antagonists? (2)
What are characteristics of partial mu agonists? (4)
- analgesia may not be as good b/c cannot agonize mu receptors to the same degree as full agonists
- decreased side effects
- bind very tightly to the mu receptor and will displace full agonists
- longer duration of action
What are the partial mu agonists? (2)
- Simbadol (cats only)
What are characteristics of kappa agonists/ mu antagonists? (4)
- analgesia less than partial or full agonists
- short duration
- decreased side effects (large animal)
- bind tightly to the mu receptor and will reverse full agonists
What drug is a kappa agonist/ mu antagonist?
What side effects do dogs get from opioids? (5)
sedation (euphoria), dysphoria, miosis, hypothermia (thermoregulatory center is reset), panting
What side effects do horses get from opioids? (3)
dysphoria/ excitement, compulsive stall pacing, colic (decreased intestinal motility)
What side effects do cats get from opioids? (2)
dysphoria/ excitement, hyperthermia
How long do the mu agonists last?
- 6-8 hours
- EXCEPT fentanyl (only about 20 minutes)
What are the cardiac effects of opioids? (2)
- bradycardia d/t stimulation of vagal nuclei centrally (responsive to atropine or glycopyrrolate)
- increased myocardial contractility d/t increased sympathetic tone
What are the vascular effects of opioids? (2)
- vasodilation d/t histamine release
- decreased BP
What are the respiratory effect of opioids? (4)
- decreased respiratory rate esp. if animal is unconscious
- decreased tidal volume
- higher arterial partial pressures of CO2 are tolerated before respirations increase
- cough suppression
What are the GI effects of opioids? (5)
- increased salivation
- initial defecation
- peristalsis decreases, segmental contractions increase (constipation)
- sphincters contract
What are the urinary effects of opioids? (3)
- urine production decreased
- increased ADH release (morphine)
- sphincters tighten (urine retention)
How are opioids eliminated from the body?
- metabolized in the liver
- duration of action can be shortened by opioid antagonists
What is the opioid antagonist?
What are the effects of partial agonists and agonist-antagonists? (5)
analgesia, less sedation, less cardiopulmonary depression, less addictive, can be used to partially reverse opioid agonists
What are the effects of opioid antagonists? (3)
fully displace agonists from the receptor, all opioid effects can be eliminated (sedation and analgesia gone), very small doses can be given to partially reverse the effects of the agonist (sedation reversed, analgesia remains)
What is neuroleptanalgesia?
- combination of agonists and agonist-antagonists used clinically with sedatives and tranquilizers to provide analgesia and sedation
- animal may or may not be awake
- may response to auditory stimuli
What are potential cardiopulmonary effects with neuroleptanalgesia? (2)
- profound bradycardia
- respiratory depression
__________ can be administered transdermally.
What is the onset and duration of action of fentanyl patches? Topical (Recuvyra)?
- Patch: analgesia produced in 8-12hr, lasts 3-5 days
- Topical: analgesia produced in 1-2 hours, last up to 4 days
Describe opioid epidurals.
- opioids given epidurally to produce analgesia; use preservative free morphine (except in horses, use regular morphine)
- analgesia within 1-2 hours, lasts 8-12hours