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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
2 properties(terms) of drug-receptor interaction
- Affinity - Intrinsic activity or efficacy
26
Affinity
- How well a drug binds to receptor
27
Intrinsic activity or efficacy
- Magnitude of effect the drug has once bound
28
Full agonist
- High affinity and high intrinsic activity - Able to generate maximal response from receptor - Stimulate both mu and kappa - Ex. morphine
29
Partial agonist
- Submaximal effect compared with full agonist - Low intrinsic activity - *Less analgesia - Ceiling effect - Higher affinity
30
Example of partial agonist
- 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
Antagonist
- 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
Inappropriate use of antagonist
- May cause the development of intense acute pain and activation of SNS
33
Competitive antagonist
- Can DISPLACE opioid agonists from Mu and Kappa receptors
34
Opioid antagonist examples
- Naloxone - Naltrexone
35
Naloxone
- Pure mu, kappa, delta antagonist - Can reverse all opioid agonist effects - Duration of action: 30-60 mins - Watch for re-narcotization
36
Naltrexone
- Clinical effects last ~2x longer than nalozone - Not readily available (may used in wildlife immobilization)
37
Agonist-antagonist
- Agonist effects at one receptor (kappa) but antagonist effect on another receptor (mu)
38
Example of an agonist-antagonist
- Butorphanol o Kappa receptor agonist o Mu receptor antagonist o Ceiling effect o Maintains analgesia (kappa)
39
Efficacy
- Maximum effect that a drug can produce regardless of dose
40
Potency
- 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
Potency is compared to morphine on an ‘equal-analgesic basis’
- Morphine was the first = 1 - Meperidine = 1/5 - Fentanyl 10,000
42
Mild and short example (efficacy vs. duration)
- Meperidine
43
Profound and long example (efficacy vs. duration)
- Morphine - Hydromorphone - Methadone
44
Buprenorphine efficacy and duration
- Moderate effect - Long duration
45
Fentanyl, sufentanil efficacy and duration
- Profound effect - Short duration
46
Opioid pharmacology
- 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
IV, IM: opioids systemic administration
- Onset rapid (except buprenorphine) - Histamine release after IV administration (morphine, meperidine)
48
Continuous rate infusions (CRI)
- 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
SC: opioid systemic administration
- Unreliable absorption - Great individual variability in pain relief - Ex. high-concentrated formulation of buprenorphine
50
High-concentration formulation of buprenorphine
- SC - Up to 24h postoperative analgesia - May be administered up to 3 consecutive days
51
Buccal (oral transmucosal, OTM)
- Non-invasive and pain-free - Minimal physical restraint required - Bypass first-pass GI clearance=allows higher bioavailability - Ex. buprenorphine
52
Buprenorphine buccal administration
- 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
Transdermal administration: fentanyl patch
- Human safety consideration - Evolved to reduce potential to abuse - Species differences how skin effects drug movements
54
Fentanyl patch evolved to reduce potential abuse
- Reservoir: filled with liquid - Drug-in adhesive matrix: active drug mixed with polymer
55
Fentanyl patch bioavailability and delayed onset: dogs
- 63% - 12-24hours (duration 3 days)
56
Fentanyl patch bioavailability and delayed onset: cats
- 35.9% - 8-12 hours (duration up to 5 days)
57
Need to continue pain assessment and monitoring with transdermal administration
- 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
Transdermal fentanyl solution (recuvyra) (in the states)
- 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
Epidural/spinal administration
- 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
Lower lipid solubility drugs and epidural/spinal administration
- 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
Fentanyl epidural/spinal administration
- Short duration - Segmental analgesia - Doesn’t travel very far - Ex humans and epidural catheter for post pain management
62
Intraarticular administration
- 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

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