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APEX > Pharmacology 2 - Opioid agonists/antagonists > Flashcards

Pharmacology 2 - Opioid agonists/antagonists Flashcards

1
Q

What are the 4 steps of pain transmission?

A

Transduction
Transmission
Modulation
Perception

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2
Q

What is hyperalgesia?

A

Increased response to a painful stimulus

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3
Q

What is allodynia?

A

Decreased threshold to a painful stimulus

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4
Q

How is pain transmitted?

A

Through a 3 neuron pathway
First order neuron: periphery to dorsal horn via spinothalamic tract
Second order neuron: from dorsal horn to thalamus
Third order neuron: from thalamus to cerebral cortex

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5
Q

What is the most important site of modulation?

A

Substantia gelatinosa in the dorsal horn (Lamina II and III)

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6
Q

When is pain inhibited?

A
  1. Spinal neurons release GABA and glycine

2. Descending pain pathway release NE, 5-HT, and endorphins

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7
Q

Where does the descending pain pathway begin? end?

A

Begins in the periaqueductal gray and rostroventral medulla

Ends in the substantia gelatinosa

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8
Q

How is pain augmented?

A

Wind up & central sensitization

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9
Q

What are the 4 opioid receptors?

A

Mu
Delta
Kappa
ORL1 (not relevant)

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10
Q

Opioid MOA (6 steps)

A
  1. Opioids bind to receptor
  2. G-protein is activated
  3. Adenylate cyclase is inhibited
  4. cAMP production is decreased
  5. Ca++ conductance is decreased
  6. K+ conductance is increased
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11
Q

What does decreased Ca++ conductance result in with pain modulation?

A

Decreased NT release in presynaptic neuron

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12
Q

What does increased K+ conductance result in with pain modulation?

A

Decreased RMP
More resistant to depolarization
Hyperpolarization of postsynaptic neuron

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13
Q

Where are opioid receptors located (3 locations)?

A

Brain: periaqueductal gray, locus ceruleus, and rostral ventral medulla
Spinal cord: primary afferent neurons in dorsal horn and interneurons
Peripheral: sensory neurons and immune cells

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14
Q

What are the precursors of opioid receptors (3)?

A
  1. Pre-proopiomelanocortin: endorphins (Mu receptor)
  2. Pre-enkephalin: enkephalins (Delta receptor)
  3. Pre-dynorphins: dynorphins (Kappa receptor)
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15
Q

Mu1 receptor symptoms

A 
ANALGESIA (supraspinal and spinal)
BRADYCARDIA
Miosis
Hypothermia
Urinary retention
Euphoria
Low abuse potential
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16
Q

Mu2 receptor symptoms

A

ANALGESIA (spinal only)
RESPIRATORY DEPRESSION
CONSTIPATION
PHYSICAL DEPENDENCE

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17
Q

Mu3 receptor symptoms

A

IMMUNE SUPPRESION

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18
Q

What drug increases biliary pressure the LEAST?

A

Meperidine

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19
Q

How to decrease biliary pressure with opioids?

A

Glucagon or nalaxone

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20
Q

What opioids have histamine releasing properties?

A

Morphine, meperidine, & codeine

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21
Q

What gender is more sensitive to opioids?

A

Women

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22
Q

What is morphine associated with in women?

A

Greater analgesic potency
Decreased postoperative opioid consumption
Slower onset of action
Longer duration of action

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23
Q

Opioids: most potent to least potent

A

Sufentanil > Remifentanil = Fentanyl > Alfentanil > Hydromorphone > Morphine > Meperidine

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24
Q

Which opioid is the standard to which all other opioids are compared?

A

Morphine

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25
Q

What is tolerance of opioids most likely due to?

A

Receptor desensitization and increased synthesis of cAMP

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26
Q
  1. What does tolerance develop to?

2. What does tolerance NOT develop to?

A
  1. Analgesia, sedation, euphoria, resp. depression, and emetic effects
  2. Miosis and constipation
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27
Q

Early signs and symptoms of withdrawal from opioids?

A

Diaphoresis, anxiety/restlessness, and insomnia

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28
Q

Later signs and symptoms of withdrawal from opioids?

A

Abdominal pain and N/V

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29
Q

Fentanyl and meperidine withdrawal symptoms time line

A

Onset: 2 - 6 hours
Peak: 6 - 12 hours
Duration: 4 - 5 days

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30
Q

Morphine and heroin withdrawal symptoms time line

A

Onset: 6 - 18 hours
Peak: 36 - 72 hours
Duration: 7 - 10 days

31
Q

Methadone withdrawal symptoms time line

A

Onset: 24 - 48 hours
Peak: 3 - 21 days
Duration: 6 - 7 weeks

32
Q
  1. Which opioids have active metabolites?

2. Which do not?

A
  1. Meperidine and Morphine

2. Sufentanil, remifentanil, alfentinil, fentanyl, and dilaudid

33
Q
  1. What metabolites does morphine posses?

2. Active or inactive?

A
  1. Morphine 3- gluconaride and Morphine 6- gluconaride

2. 3 = inactive; 6 = active

34
Q

What opioid should renal failure patients not receive?

A

Morphine - unable to eliminate it even with dialysis, thus respiratory depression and toxicity can occur

35
Q

Who else (other than renal failure) may develop M6G toxicity and accumulation?

A

Chronic morphine use with normal renal function

36
Q
  1. What does M3G cause?

2. What does M6G cause?

A
  1. Hyperalgesia, agitation, myoclonus, delirium

2. Resp. depression, drowsiness, N/V, coma

37
Q

What does meperidine result in?

A

Decreased seizure threshold and increased CNS excitability

38
Q

S/S of meperidine CNS excitability?

A

Muscle twitches, seizures, tremors

39
Q

Who should meperidine be avoided in?

A

Elderly and patients on dialysis

40
Q

What is remifentanil metabolized by?

A

Tissue and plasma esterases

41
Q

How is remifentanil dosed?

A

IBW

42
Q

What is meperidine metabolized to?

A

Normeperidine

43
Q

What drugs should be avoided with meperidine?

A

MAOI’s due to the risk of serotonin syndrome (Meperidine acts like an SSRI)

44
Q

S/S of serotonin syndrome?

A 
Hyperthermia
Mental status changes
Hyperreflexia
Seizures
Death
45
Q

Examples of MAOI’s?

A

Phenylxine
Isocarboxazid
Tranylcypromine

46
Q

What drug is meperidine structurally related to?

A

Atropine - anticholinergic effects (tachycardia, mydriasis, drymouth)

47
Q

What receptor is stimulated with meperidine to decrease shivering?

A

Kappa

48
Q

How fast is alfentanils effect site concentration time?

A

~ 1.4 minutes
This is due to the low pKa of it (6.5)
More unionized particles (~ 90%) and faster onset

49
Q

What drug inhibits metabolism of alfentanil?

A

Erythromycin - increased respiratory depression risk/time

50
Q

How is alfentanil metabolized?

A

CYP3A4 (cytochrome p450 enzymes)

Renal failure does not effect clearance

51
Q

Big complication with pain control after remifentanil?

A

Hyperalgesia - tend to increase opioid use in post op period

52
Q

How to decrease opioid induced hyperalgesia after remifentanil infusions?

A

Ketamine and magensium

53
Q

Why cant remifentanil be used intrathecally or via epidural?

A

It has glycine (inhibitory NT) as a buffer when reconstituted which can cause skeletal muscle weakness

54
Q

What circumstances is methadone best used for?

A

Opioid withdrawal treatment
Chronic pain management
Cancer pain

55
Q

Which opioid is prepared as a racemic mixture?

A

Methadone

56
Q

By what three mechanisms does methadone reduce pain?

A

NMDA antagonism
Monoamine reuptake inhibition in synaptic cleft
Mu receptor agonism

57
Q

What potential complication can arise with methadone use?

A 
QT prolongation (very rare)
Can lead to torsades de pointes
58
Q

Whats the most common cause of increased skeletal muscle rigidity?

A

Rapid IV administration of opioids

59
Q

What is the best treatment for skeletal muscle rigidity?

A

Paralyzing and intubating

60
Q

What is the MOA of opioid induced skeletal muscle rigidity?

A

Mu receptor stimulation of the SNS (dopamine and GABA motor pathways)

61
Q

RESPIRATORY complications with opioid induced SKM rigidity?

A 
Hypoxia
Hypercarbia
Increased O2 consumption
Decreased SVO2
Decreased FRC
Decreased thoracic compliance
Decrease minute ventilation
62
Q

CV complications with opioid induced SKM rigidity?

A

Increased CVP, PAP, PVR

63
Q

OTHER complications with opioid induced SKM rigidity?

A

Increased ICP

Increased intragastric pressure with mask ventilation

64
Q

Common characteristics of partial agonists?

A

Have a ceiling effect
Less efficacious as full agonists
Can cause acute opioid withdrawal in opioid addicts
Used in patients who cant tolerate full agonists
Produce analgesia without respiratory depression
Less likely to be abused
Can cause dysphoric reactions

65
Q

Dose of narcan?

A

1 - 4 mcg/kg or 20 - 40 mg IV

66
Q

DOA of narcan?

A

30 - 45 minutes

67
Q

Narcan use?

A

RD with opioid overdose
RD in neonate whose mother received opioids
Treatment of opioid overdose

68
Q

What receptors does narcan work on?

A

Mu, kappa, and delta (Mu the most!)

69
Q

What complications arise with narcan?

A
  • SNS stimulation (tachycardia, pulm. edeam, HTN, arrythmias, excitation, anxiety, etc.)
  • N/V (less with slow titration over 2 - 3 minutes)
70
Q

What is methylnaltrexone?

Whats the problem with its use?

A
  • An opioid reversal agent
  • Its a quartinary amino group (cant cross BBB and reverse RD)
  • Better used for peripheral symptoms (bowel dysfunction)
71
Q

Problem with narcan?

A

Very high first pass metabolism (may need continuous infusion or multiple doses if narcotic has a longer DOA than the narcan)

72
Q

Nalmefene dosing

A

0.1 - 0.5 mcg/kg

73
Q

Benefit of naltrexone?

A

Does not undergo first pass metabolism and has a very long half life of around 24 hours

APEX (3 decks)

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