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Clinical Neurology > Pharm - Opiods > Flashcards

Pharm - Opiods Flashcards

1
Q

Physiologic pain

A

Serves a defensive role
Acute in nature (e.g. labor, surgery and acute trauma)
Easy to manage

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2
Q

Pathological Pain

A

Serves no known beneficial purpose. Chronic in nature, spontaneous, Characterized by: Low pain threshold to both noxious and innocuous stimuli. Associated with nerve damage (e.g. trauma, amputation, diabetes mellitus, HIV and varicella zoster VZV )
Difficult to treat

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3
Q

Ascending Pathway for pain transmission

A

Primary afferent nociceptors -> Dorsal horn cells -> spinothalamic tracts -> VPM -> Cortex

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4
Q

Descending Pathway (Inhibitory Regulation)

A

Originates from frontal cortex, amygdala and cingulate cortex. Synapse on the Periaqueductal gray (PAG), then Rostral ventromedial medulla (RVM) and finally on the dorsal horn cells

Major neurotransmitters include 5HT, norepinephrine, glycine, GABA and opioids

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5
Q

Receptor subtype

u (mu)

A
  1. Supraspinal and spinal analgesia
  2. Sedation and inhibition of respiration
  3. Slow GI transit
  4. Modulation of hormones and neurotransmitter release

Physiology:
Stabilize neuronal membrane secondary to enhancing K+ conductance (hyperpolarizing neuron), inhibition of voltage-gated Ca2+ channels

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6
Q

Receptor subtype

d (delta)

A
  1. Supraspinal and spinal analgesia
  2. Modulation of hormones and neurotransmitter release

Physiology:
Stabilize neuronal membrane secondary to enhancing K+ conductance (hyperpolarizing neuron), inhibition of voltage-gated Ca2+ channels

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7
Q

Receptor subtype

k (kappa)

A
  1. Supraspinal and spinal analgesia
  2. Slow GI transit
  3. Psychomimetic effects

Physiology
κ-Opioid receptor activation by agonists is coupled to the G protein Gi/G0, which subsequently increases phosphodiesterase activity. Phosphodiesterases break down cAMP, producing an inhibitory effect in neurons

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8
Q

Strong Agonists

A

Morphine, Heroin, Methadone, Fentanyl, Meperidine, Levorphanol

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9
Q

Mild to Moderate Agonists

A

Codeine, Oxycodone, Hydrocodone, Diphenoxylate

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10
Q

Weak Agonist

A

Propoxyphene

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11
Q

Mixed Agonists /Antagonists

A

Pentazocine

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12
Q

Partial Agonists

A

Buprenorphine

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13
Q

Antagonists

A

Naloxone, Naltrexone,

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14
Q

Codeine

A

Naturally Occurring Opioids
Mild to Moderate Agonists

undergoes hepatic de-amination to morphine
genetic polymorphism of CPY2D6 and CPY3A4 of clinical significance
oxycodone, hydrocodone, effective mild analogues of codeine

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15
Q

Morphine

A

Naturally Occurring Opioids
Strong Agonists
Hepatic metabolism to M3G or M6G, (M6G has analgesic effects)
Hydromorphone, widely used more potent morphine derivative

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16
Q

Methadone

A

Synthetic Opioid receptor Agonist
Strong Agonists

Long plasma t½ (lipophilic, plasma protein binding) , used mostly for chronic pain in terminally ill cancer patients

High risk of respiratory depression, QT prolongation → torsades de pointes

17
Q

Meperidine

A

Synthetic Opioid receptor Agonist
Strong Agonists

Poor oral bioavailability, metabolites may cause seizures
Similar analgesic efficacy as morphine, less potent
Causes mydriasis rather than miosis – unlike other opioids

18
Q

Fentanyl

A

Synthetic Opioid receptor Agonist
Strong Agonists

Short acting, 100x more potent than morphine, highly lipophilic
Sufentanil, alfentanil and ramifentanil are synthetic analog
Available in transdermal patch for slow delivery

19
Q

Butorphanol

A

Mixed Agonists / Antagonist

Agonist at κ, partial agonist at u-opioid receptor
Analgesia with milder euphoria
Clinical applications:
treatment of opioid addiction
Maintenance in balance anesthesia, labor pain

20
Q

Buprenorphine

A

Partial Agonists

Partial agonist at µ, antagonist at κ-opioid receptors
Clinical applications:
Pain, chronic (moderate or severe), long-term management of pain

21
Q

Nalbuphine

A

Mixed Agonists / Antagonist

Agonist at k, antagonist at u
Effective analgesic, (moderate to severe pain), preoperative, postoperative, obstetrical analgesia
high psychological dysphoria may occur

22
Q

Naloxone

A

Opioid Receptor Antagonists

Competitive antagonist at u, and κ-opioid receptors, t½ is shorter than that of morphine
Administered parenterally
antidote for opioid intoxication / overdose – known or suspected
Reversal of opioid activity (respiratory distress)

23
Q

Naltrexone

A

Opioid Receptor Antagonists

Administered orally, can be used in outpatient settings
Pure competitive opioid antagonist
For treatment of opioid dependence, relapse, following detoxification, prophylaxis
Alcohol withdrawal

24
Q

Untoward Effects of Opioids

Dependence

A

Psychological
Distinct from physical dependence or analgesia and is mediated by a different neuronal system (ventral striatum)
Involves interactions between the opioids and dopaminergic system (nucleus accumbens)

Physical
Marked with diaphoresis, insomnia, restlessness, abdominal cramps, nausea, vomiting and diarrhea

25
Q

Untoward Effects of Opioids

Tolerance

A

mediated (at least in part) via NMDA signaling
Mainly cosmetic in nature
Rotation therapy may be helpful

Minimal or no tolerance
Miosis and Constipation

Moderate tolerance
Bradycardia

High Tolerance (most likely to down regulate)
Analgesia, Euphoria, dysphoria, Mental clouding, sedation, Respiratory depression, Anti diuresis, Nausea and Vomiting, Cough suppression
26
Q

Untoward Effects of Opioids

Respiratory depression

A

Respiratory depression
Decrease sensitivity of chemo-sensitive neurons to PCO2
Occurs at therapeutic doses (unlike case with CNS depressants)
Most common cause of death in acute opioid poisoning

27
Q

Untoward Effects of Opioids

GI Disturbances

A

GI Disturbances
Epigastric distress & biliary colic (may be confused with angina)
increase tone of pyloric sphincter and enhance and decrease peristaltic movements
Constipation is common opioid side effect

28
Q

Untoward Effects of Opioids

Miosis

A 
Miosis
Independent of tolerance
A diagnostic tool 
u and k-mediated 
Involves the nucleus of Edinger Westphal

Exception is Meperidine which causes Mydriasis

29
Q

Untoward Effects of Opioids

Nausea and vomiting

A

Nausea and vomiting
Often transient, can limit compliance
Involves the area postrema

30
Q

Untoward Effects of Opioids

Hypotension and bradycardia

A

Impairment of sympathetic compensatory responses → orthostatic hypotension (e.g. with morphine)
common with rapid iv administration of large doses of opioids (courtesy of non-specific mast cell degranulation)

Synthetic opioids (meperidine, diphenoxylate, fentanyl) and short-acting opioids do not evoke histamine release

31
Q

NSAIDs and acetaminophen

A

Decrease prostaglandin synthesis, decrease pain sensation

32
Q

Adrenergic agonists

A

Clonidine, effective in both acute and chronic pain state

33
Q

NMDA receptor antagonists

A

Ketamine and dexamethorphan (for chronic pain syndrome and post operative pain)
Ketamine, effective for acute severe pain, strong psycho mimetic effects

34
Q

Antidepressants

A

Amitriptyline, nortriptyline and imipramine
Treatment of chronic pain not responsive to opioids
Venlafaxine and duloxetine, used for neuropathic pain

35
Q

Gabapentin

A

Synthetic GABA analog, inhibits voltage-gated Ca2+ channels
Widely used for chronic pain and post-operative pain state
Erratic oral bioavailability – a problem

36
Q

Pregabalin

A

GABA analog, more potent, faster on set of action, predictable bioavailability than gabapentin
Inhibits voltage gated Ca2+ channels in the CNS
Effective in neuropathic pain, fibromyalgia, spinal cord injury

37
Q

Lamotrigine

A

Na+ channel blocker, for neuropathic pain, trigeminal neuralgia
Skin reaction is common with its use

38
Q

Carbamazepine

A

Na+ channel blocker, primarily for treatment of trigeminal neuralgia
may cause hypotension

Clinical Neurology (18 decks)

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