Opiates and Opioids Flashcards
Define nociception
ability to sense or perceive pain
Define analgesia
absence of pain in response to stimuli that are normally painful without loss of consciousness
Define hyperalgesia
extreme responsiveness to stimuli that are usually only modestly painful
Define allodynia
pain caused by a stimulus not normally evoking pain
Define the path of pain transmission
detection of painful stimulus at nociceptor > sensory afferents (Ad or C) > Dorsal root ganglion > spinal cord > spinothalamic tracts in brain > perception
What is Substance P?
an important neurotransmitter in pain from DRG afferents at tissue and level of spinal cord
- pro-inflammatory
- detected by tachykinin receptors (NK1, NK3)
- activates pain pathway
How does acupuncture alleviate pain?
activates endogenous pathways that help suppress pain
What drug classes have a peripheral site of analgesic drug action?
NSAIDs and corticosteroids; act on the nociceptor
What drug classes have a nerve block site of analgesic drug action?
Local anesthetics; acts on the sensory afferents
What drug classes have an epidural site of analgesic drug action?
Opioids, alpha2 agonists, NMDA antagonists, local anesthetics; act at the level of the spinal cord
What drug classes have a CNS site of analgesic drug action?
Alpha2 agonists, NMDA antagonists, opioids, cannabinoids
What three opiates are used clinically?
morphine, codeine, and papaverine
What is the difference between opiates and opioids?
Opiates are naturally occurring alkaloids derived from opium (e.g. morphine, codeine, papaverine)
Opioids are drugs/substances that bind opioid receptors; used for their pain-relieving effects; includes natural and synthetic compounds
Which DEA-class of drugs have no currently accepted medical use?
Class I (heroin, bufotenine)
What are endogenous opioids?
“gut-brain” peptides released in response to painful stimuli, prolonged physical exertion, or during a fight or flight response that activate endogenous opioid receptors
What are the four classes of endogenous opioids?
- Enkephalins (met & Leu) - pentapeptides
- Endorphins (beta) - larger (31 amino acids)
- Dynorphins (A & B) - intermediate size
- Endomorphins (1 & 2) - tetrapeptides w/ mu specificity
What are the CNS effects of endogenous opioids?
analgesia, nausea/vomiting (dogs), mood alteration, depressed breathing, sedation
What are the GI effects of endogenous opioids?
constipation (decr propulsive activity)
What are the cardiovascular effects of endogenous opioids?
cardiac depression, hypotension
What are the 3 major receptors acted on by opioids?
Mu, kappa, and delta
What G-protein do opioid receptors associate with?
Gi
What are the general effects of opioids?
decrease the activities of the brain, GI system, and CVS
Describe a mixed agonist-antagonist
a drug that stimulates some receptor subtypes, but antagonizes other subtypes of the same receptor family
Describe the analgesic properties of opioids
- decrease pain sensation without loss of consciousness
- Requires two levels of action:
- Spinal cord (modulation)
- Supraspinal level (perception)
Describe the spinal cord modulation effects of opioids that result in analgesia
- decr substance P release from sensory afferents
- decr postsynaptic actions of substance P
Describe the supraspinal level (perception) effects of opioids resulting in analgesia
- decr affective response to pain
- decr fear/anxiety assoc. w/ pain
Describe the sedative properties of opioids
- initial calming effect that may be followed by sleep, coma, and then death
-
additive depressive effects when used with other CNS depressants
- decreases anesthetic requirement in most animals
Describe the ventilatory effects of opioids
- doses that causes analgesia also cause ventilatory depression in most species
- opioids depress brainstem sensitivity to PCO2 > drive to breath decreases
Describe the emetic/nausea effects of opioids
Caused by triggering of chemoreceptor trigger zone in brainstem; species differences- dogs sensitive
Do opioids have cough suppressant effects?
yes; species differences
- dogs = codeine, butorphonal
- cats = butorphonal
What are the effects of opioids on the pupils?
Species-specific effect
- dogs, rabbits, humans = miosis
- cats, horses, sheep, non-human primates = mydriasis
- birds = no change
What type of effects do opioids have on mood?
variable (euphoria/dysphoria)
What effects do opioids have on the GI tract?
GI stasis - involves CNS mechanisms and actions of the GI system, decreased propulsion
What are the effects of opioids on the cardiovascular system?
cardiovascular depression; mild decr in heart functions
- decr HR in dogs
- decr blood pressure
Is opioid tolerance common?
yes; involves CNS & peripheral organs
What are the symptoms of opioid toxicity?
In dogs:
- depressed ventilation
- fixed pinpoint pupils
- coma or marked CNS depression
Tx: naloxone and supportive therapy
What are the general precautions for opiod use?
- felines
- pregnancy (decr newborn respiration)
- shock (congestive heart failure)
- pulmonary dz
- liver dz (metabolized in liver)
What are the signs of Opioid Withdrawal Syndrome?
- anxiety
- hypertension
- nausea
- diarrhea
- dysphoria
