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Pharmacology > Analgesics > Flashcards

Analgesics Flashcards

1
Q

Analgesia and Pain pathway

A
  • Noiceptors are stimulated by pain and originate in the periphery
  • They send action potential to the dorsal horn of the spinal cord
  • Synapses with secondary neuron via glutamate and neuropeptide transmitters send action potential to brain where we “sense pain”

Basically, there are opioid receptors at all these locations which can inhibit pain

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2
Q

What are the four different opiod receptors?

A

mu, kappa, delta, sigma

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3
Q

What are engogenous agonists of Mu receptors?

A

Beta endorphin

Met-encephalin

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4
Q

Example drugs that act on Mu receptors?

A

Morphine

Fentanyl

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5
Q

Clinical effects of Mu receptor agonists?

A

Supraspinal analgesia µ1

Respiratory depression µ2

Physical dependence

Muscle rigidity

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6
Q

What are the clinical effects of Kappa (K) agonists?

A

Sedation

Spinal analgesia

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7
Q

Example of Kappa endogenous agonists?

A

Dynorphin

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8
Q

Example Kappa agonist drugs?

A

Morphine

Nalbuphine

Butorphanol

Oxycodone

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9
Q

Example delta receptor clinical effects?

A

Analgesia

Behavioral

Epileptogenic

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10
Q

What are endogenous agonists of delta receptors?

A

Leu-enkephaline

Beta endorphin

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11
Q

Clinical effects of sigma activation?

A

Dysphoria

Hallucinations

Respiratory stimulation

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12
Q

Example sigma receptor agonists?

A

Pentazocine

Nalorphine

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13
Q

What is the mechanism of action of opioids binding to thier receptors?

A

Opioid receptors inhibit the presynaptic release of excitatory neurotransmitters (Ach, Substance P, NE, 5HT) which are normally released by noiceptive neurons (pain receptors)

-

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14
Q

Where are opioid receptors located?

A

Peripheral and CNS tissue

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15
Q

How can opioids be delivered?

A

Systemically or directly (spinal analgesia)

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16
Q

What is the benefit of direct spinal analgesia with opioids?

A

This spinal action provides a regional analgesic effect while reducing the unwanted respiratory depression, nausea and vomiting, and sedation that may occur from the supraspinal actions of systemically administered opioids.

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17
Q

Upon activated opioid G-proteins at the membrane, what are the two main ways in which opioids stop the transmission of the pain signal (Action potential)

A
  1. MOR (Mu opioid receptors) are activated and close voltage gated Ca2+ channels on presynaptic nerve terminals, inhibiting NT release
  2. They open K+ channels and hyperpolarize the cell, inhibiting postsynaptic neurons
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18
Q

Sites of opioid action of ascending pathways?

A
  • They can act directly at the noiceptor terminals
  • The Dorsal Root Ganglion (DRG) and spinal cord (Dorsal horn)
  • Also possible sites in the amygdala (Anterior cingulate gyrus, ventral posterolateral nucleus of the thalamus)
19
Q

Sites of opioid action of descending pathways?

A

In the descending (modullatory) pathway, opioids inhibit neurons by activating descending “inhibitory neurons” that send processes to the spinal cord and inhibit pain transmission neurons. The Inhibtion of inhibitory neurons acts at many different sites as shown below:

  • Pain-modulating neurons in the midbrain and medulla including the midbrain aqueductal gray area
  • Rostral ventral medulla
  • Locus coeruleus
20
Q

Part of tolerance and withdrawal from opioids involves the NMDA-receptor ion channel complex, what drug would antagonize this receptor and block tolerance development?

A

Ketamine (NMDA antagonist)

21
Q

What is opioid-induced hyperalgesia?

A

Chronic use can increase the sensation of pain, including morphine, fentanyl, and remifentanil. This is why chronic opioid use for treating pain is controversial.

22
Q

What are the central nervous system effects of opioids?

A

u (Mu) receptors in the CNS cause:

  • Analgesia (Emotional and physical)
  • Euphoria
  • Sedation (Amplified with sedatives, deep sleep)
  • Respiratory depression (Increases alveolar PC02, and apneic threshold)
  • Supression of the cough reflex, especially codeine
  • Miosis (constriction of pupils)
  • Truncal rigidity
  • Nausea and vomitting
  • Homeostatic regulation of temperature (u agonist=hyperthermia; k agonist=hypothermia)
  • Reduce stage 3 and 4 sleep paterns
  • Tolerance (with heavy use)
23
Q

What are the peripheral nervous system effects of opioids?

A
  • Constipation
  • Contract biliary smooth muscle
  • Depression of renal function
  • May prolong labor, inhibiting uterine contraction
  • Stimulate the release of ADH, prolactin, and somatotropin
  • Inhibit the release of luteinizing hormone
  • Pruritus, flushing of the skin (peripheral histamine release)
24
Q

What are the endogenous opioid peptides?

A

Endorphins

Pentapeptide enkephalins (met-enkephalin)

Leucine-enkephalin (leu-enkephalin)

Dynorphins

25
How much more potency does morphine-3-glucuronide (M3G) have compared to morphine?
10% of morphine is converted to this active metabolite, which is 4-6 times more potent than morphine
26
T or F. Codeine, oxycodone, and hydrocodone all have active metabolites
Codeine -\> demethylated to morphine, which is then conjugated Hydrocodone -\> metabolized to hydromorphone -\> H3G Oxycodone -\> metabolized to oxymorphone -\> O3G
27
If someone is shivering post operatively, what is the best drug to give them?
Meperidine, an a2 adrenoreceptor
28
Example of a mixed agonist-antagonist
Buprenorphine
29
What drugs can cause a histamine release after a bolus?
—Morphine Hydromorphone Meperidine
30
Spinal / epidural may lead to intense pruritus over lips and torso – up to?
70-100% of patients Kappa agonist (Nalbuphine, Butorphanol) may help or avoid
31
Mu (u) agonists in from most potent to least
Remifentanil \> Sufentinal \> Fentanyl \> Alfentinal \> Hydromorphone \> Morphine \> Meperidine
32
Mu (u) partial or weak agonist from most to least potent
Buprenorphine (sigma/kappa antagonist) \> Butorphanol (also kappa agonist)
33
Kappa agonists from least to most affinity
Morphine \> Sufentinal (also sigma agonist) \> Nalbuphine \> Butorphanol
34
What receptors to opioid antagonists mostly act on, and what is there onset?
Mu (u), _Onset:_ 1-3 min IV Naloxone, naltrexone, nalmefene _Dose_: 0.4 - 2 mg every 2-3 min to affect (Naloxone) _Duration_: Naltrexone (~48h PO) \> Nalmefene (8-10h IV) \> Naloxone (1-2h IM) No tolerance or withdrawal
35
Buprenorphine
(Mixed agonist/antagonist) potent/long-acting - Partial u receptor agonist - sigma and kappa antagonist - Can antagonize the stronger opioid agonists such as morphine - Used for opioid addiction, combined with Naloxone = Suboxone - Can cause respiratory depression/death when combined with BZ at high doses
36
Meperidine
- Older opioid, significant anti-muscarinic effects - Neg. inatropic effects on the heart - Potential for producing seizures secondary to it's active metabolite, normeperidine Contraindicaitons: Tachycardia, renal failure
37
Nalbuphine
(Mixed agonist/antagonist), stong k receptor agonist/partial u receptor antagonist - Given PO - Respiratory depression at high doses, and cannot be readily reversed by Naloxone - Equipotent to morphine for analgesia and can be effective for pruritis at low doses
38
Butorphanol
- Analgesia equivalent to nalbuphine but more sedation at the same analgesic dose - Butorphanol is a K agonist/partial u receptor agonist/antagonist
39
Tramadol
Metabolites block serotonin and norepinephrine uptake -Only partially antagonized with naloxone, low u receptor affinity _Dose_: 50-100mg PO/ q6h -Seizure contraindications, serotonin syndrome especially with SSRI medications -
40
NSAIDs Mechanism of action
Inhibit cyclooxygenase (COX), prostaglandin synthesis -COX normally produces prostaglandin H from arachidonic acid
41
COX-2 Inhibitors
Celecoxib - Do not affect platelet function at their usual doses, GI safety is improved - However, increase edema, hypertension, thrombosis, stroke, and myocardial infarction
42
Non-selective COX inhibitors
—**Ibuoprofen**, **Ketorolac**, **Diclofenac**, Naproxen, Indomethacin, Aspirin, Piroxicam, and Many more - Aspirin and acetominophen also inhibit COX - Reduce opioid dosing 25-45% - Controversial on bone healing
43
Acetominophen, weaker than NSAIDS but analgesic -COX 1/2 inhibitor, thought to now affect serotonin pathways and other noiceptor pathways _Onset_: 5-10 min _Duration_: 4-6 hours _Dosing_: —12.5 mg/kg q 4 h or 15 mg/kg q 6 h -Contraindicated in hepatic failure

Pharmacology (17 decks)

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