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ANESTHESIA > 12 – Opioids I > Flashcards

12 – Opioids I Flashcards

1
Q

Opium

A
  • Unrefined extract from poppy
  • Contains ~20 naturally occurring pharmacologically active compounds
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2
Q

Opiates

A
  • Group of purified natural agents
  • Morphine
  • Codeine
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3
Q

Opioid

A
  • Any natural, synthetic, endogenous substance with morphine-like properties
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4
Q

Endogenous opioids peptides

A
  • Small molecules that are naturally produced in CNS and various glands throughout the body (pituitary and adrenal)
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5
Q

4 distinct families of endogenous opioid peptides

A
  • Beta-endorphin (mu)
  • Enkephalins (delta)
  • Dynorphins (kappa)
  • Nociception (NOP)
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6
Q

Anatomical distribution of opioid receptors

A
  • Supraspinal
  • Spinal
  • Periphery
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7
Q

Supraspinal distribution of opioid receptors

A
  • Brain stem (periaqueductal grey area)
  • Hypothalamus
  • Amygdala
  • Corpus striatum
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8
Q

Spinal distribution of opioid receptors

A
  • Dorsal horn: substantia gelatinosa
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9
Q

Periphery distribution of opioid receptors

A
  • ID on the process of sensory neurons
  • **Upregulated during inflammatory-pain states
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10
Q

Opioid receptors ‘type’:

A
  • GPCRs
  • Mediate inhibition of neurotransmission and endocrine secretion
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11
Q

Opioid receptors pathway: 3 actions

A
  • Inhibit adenyl cyclase activity
  • Inhibition of pre-synaptic voltage gated Ca-channels
  • Increased K+ efflux ->neuronal hyperpolarization of post-synaptic SC projection neurons
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12
Q

Inhibition of pre-synaptic voltage-gated Ca-channels

A
  • Decreased Ca INFLUX
  • Reduce NT release
  • Inhibition of synaptic transmission of nociceptive input
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13
Q

Increased K+ efflux

A
  • neuronal hyperpolarization of post-synaptic SC projection neurons
  • inhibition of ascending nociceptive pathways
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14
Q

3 well defined types of opioid receptors

A
  1. Mu
  2. Delta
  3. Kappa
  4. (recent years: nociception receptor)
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15
Q

Mu receptor agonist effects

A
  • *profound analgesia (spinal and supraspinal)
  • Respiratory depression
  • Bradycardia
  • Sedation (dose-dependent)
  • Euphoria/dysphoria
  • Miosis
  • Hypothermia
  • Antitussive
  • Decreased GI motility
  • Urinary retention
  • Emesis
  • Anti-emetic at vomiting center
  • Minimal CV effects
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16
Q

Kappa receptor agonist effects

A
  • *spinal analgesia (mild to moderate pain)
  • Mild sedation
  • Miosis
  • Minal respiratory depression and vagally mediated bradycardia
  • Dysphoria
  • Diuresis
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17
Q

Opioid effects: clinical significance

A
  • Analgesia
  • Sedation (part of premedication)
  • Anesthetic sparing
  • Reversible
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18
Q

Opioid effects: clinical significance side effects

A
  • Bradycardia
  • Respiratory depression
  • Emesis (nausea)
  • Abuse potential
  • Dysphoria
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19
Q

Opioids in different species

A
  • Receptor distribution differs among species and within species
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20
Q

Mu receptor agonist: example in different species

A
  • CNS depression: dogs, monkeys, humans
  • Excitement and/or spontaneous locomotor activity: PAIN FREE mice, cats, horses, goats, sheep, pigs, cows
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21
Q

Morphine Mania in cats (historical)

A
  • Elicited by doses 100-fold higher than those used clinically
  • *do get mydriasis (dilated pupils)
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22
Q

Birds: opioids in different species

A
  • Raptors:
    o Mu-opioids agonists provide analgesia
    o Kappa oppioda agonists appear ineffective
  • Psittacines (buggies)
    o Kappa opioid agonists more effective than mu-opioids
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23
Q

Reptiles: opioids in different species

A
  • Mu-opioid agonists provide effective analgesia in most reptiles
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24
Q

Individual variability (pharmacogenetics)

A
  • Don’t assume every patient will respond the same way
  • *treatment should be tailored to the individual
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25
Q

2 properties(terms) of drug-receptor interaction

A
  • Affinity
  • Intrinsic activity or efficacy
26
Q

Affinity

A
  • How well a drug binds to receptor
27
Q

Intrinsic activity or efficacy

A
  • Magnitude of effect the drug has once bound
28
Q

Full agonist

A
  • High affinity and high intrinsic activity
  • Able to generate maximal response from receptor
  • Stimulate both mu and kappa
  • Ex. morphine
29
Q

Partial agonist

A
  • Submaximal effect compared with full agonist
  • Low intrinsic activity
  • *Less analgesia
  • Ceiling effect
  • Higher affinity
30
Q

Example of partial agonist

A
  • Buprenorphine
    o Higher affinity but less intrinsic activity than morphine
    o Ex. if want to give morphine=buprenorphine will block the receptor for 6-8hours (‘ceiling effect’)
31
Q

Antagonist

A
  • No intrinsic activity, but HIGH affinity
  • Rapidly reverse all opioid-induced clinical effects (including ANALGESIA)
    o Use for EMERGENCY SITUATIONS (overdose or profound respiratory depression)
  • Non-emergent situations=ALWAYS titrate to effect
32
Q

Inappropriate use of antagonist

A
  • May cause the development of intense acute pain and activation of SNS
33
Q

Competitive antagonist

A
  • Can DISPLACE opioid agonists from Mu and Kappa receptors
34
Q

Opioid antagonist examples

A
  • Naloxone
  • Naltrexone
35
Q

Naloxone

A
  • Pure mu, kappa, delta antagonist
  • Can reverse all opioid agonist effects
  • Duration of action: 30-60 mins
  • Watch for re-narcotization
36
Q

Naltrexone

A
  • Clinical effects last ~2x longer than nalozone
  • Not readily available (may used in wildlife immobilization)
37
Q

Agonist-antagonist

A
  • Agonist effects at one receptor (kappa) but antagonist effect on another receptor (mu)
38
Q

Example of an agonist-antagonist

A
  • Butorphanol
    o Kappa receptor agonist
    o Mu receptor antagonist
    o Ceiling effect
    o Maintains analgesia (kappa)
39
Q

Efficacy

A
  • Maximum effect that a drug can produce regardless of dose
40
Q

Potency

A
  • Amount of drug that is needed to produce a given effect
  • Ex. less concentration/dose required=more potent
  • *determined by affinity of drug for receptor and number of receptors available
41
Q

Potency is compared to morphine on an ‘equal-analgesic basis’

A
  • Morphine was the first = 1
  • Meperidine = 1/5
  • Fentanyl 10,000
42
Q

Mild and short example (efficacy vs. duration)

A
  • Meperidine
43
Q

Profound and long example (efficacy vs. duration)

A
  • Morphine
  • Hydromorphone
  • Methadone
44
Q

Buprenorphine efficacy and duration

A
  • Moderate effect
  • Long duration
45
Q

Fentanyl, sufentanil efficacy and duration

A
  • Profound effect
  • Short duration
46
Q

Opioid pharmacology

A
  • Highly lipid soluble
  • Hepatic transformation
  • Oral opioids in animals: poor bioavailability (high first pass effect in liver)
  • Differences in metabolisms among species
  • Some metabolites are active (analgesic and other effects)
  • Elimination: biliary and renal excretion
47
Q

IV, IM: opioids systemic administration

A
  • Onset rapid (except buprenorphine)
  • Histamine release after IV administration (morphine, meperidine)
48
Q

Continuous rate infusions (CRI)

A
  • Medication continuously administered IV to maintain consistent plasma levels and analgesia
  • Short acting mu-agonist well suited (fentanyl, remifentanil, sufentanil)
  • Morphine, hydromorphone
  • *reduction of unwanted side effects (after intermittent bolus administration)
49
Q

SC: opioid systemic administration

A
  • Unreliable absorption
  • Great individual variability in pain relief
  • Ex. high-concentrated formulation of buprenorphine
50
Q

High-concentration formulation of buprenorphine

A
  • SC
  • Up to 24h postoperative analgesia
  • May be administered up to 3 consecutive days
51
Q

Buccal (oral transmucosal, OTM)

A
  • Non-invasive and pain-free
  • Minimal physical restraint required
  • Bypass first-pass GI clearance=allows higher bioavailability
  • Ex. buprenorphine
52
Q

Buprenorphine buccal administration

A
  • Cats: acceptable bioavailability and analgesia
  • Dogs: high dose required ->cost prohibitive, risk of swallowing
  • In clinic setting: IV, IM provide better analgesia
  • Suitable for late postoperative analgesia
53
Q

Transdermal administration: fentanyl patch

A
  • Human safety consideration
  • Evolved to reduce potential to abuse
  • Species differences how skin effects drug movements
54
Q

Fentanyl patch evolved to reduce potential abuse

A
  • Reservoir: filled with liquid
  • Drug-in adhesive matrix: active drug mixed with polymer
55
Q

Fentanyl patch bioavailability and delayed onset: dogs

A
  • 63%
  • 12-24hours (duration 3 days)
56
Q

Fentanyl patch bioavailability and delayed onset: cats

A
  • 35.9%
  • 8-12 hours (duration up to 5 days)
57
Q

Need to continue pain assessment and monitoring with transdermal administration

A
  • Great individual variability in drug absorption
  • Changes in body T, skin preparation, patch placement affect rate of absorption, plasma fentanyl levels and analgesic efficacy substantially
  • Care with heating pads (increased circulation increases uptake): CAREFUL OF OVERDOSE
58
Q

Transdermal fentanyl solution (recuvyra) (in the states)

A
  • Postoperative pain control
  • Liquid solution applied to skin dorsally between shoulder blades (stratum corneum)
  • No need necessary
  • Requires RISK training
  • Applied 2-4hrs prior surgery
  • Last up to 4 days in dogs
  • No PEAK effect
  • Adverse effects are long lasting
59
Q

Epidural/spinal administration

A
  • Often used in epidural or subarachnoid space to manage ACUTE or CHRONIC PAIN
  • All are lipid soluble but solubility differs between opioids
  • *depends on how lipophilic they are
60
Q

Lower lipid solubility drugs and epidural/spinal administration

A
  • Less systemic absorption
  • Slower onset time (passage across dura matter)
  • Longer duration and further cranial migration
    o Morphine: 12-24 hours
    o Hydromorphine: 8 hours
61
Q

Fentanyl epidural/spinal administration

A
  • Short duration
  • Segmental analgesia
  • Doesn’t travel very far
  • Ex humans and epidural catheter for post pain management
62
Q

Intraarticular administration

A
  • Significant increase in mu-opioid receptors in articular and peri-articular tissues occurs after joint inflammation
  • *of morphine after arthroscopy surgery (knee, elbow) as part of MULTIMODAL ANALGESIA pain

ANESTHESIA (27 decks)

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