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Neurology > Analgesic Drugs > Flashcards

Analgesic Drugs Flashcards

1
Q

How do analgesic drugs act at sites of injury to reduce nociception and pain?

A

Decrease nociceptor sensitisation in inflammation primarily by blocking synthesis of prostaglandins

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2
Q

What do analgesic drugs suppress to reduce nociception and pain?

A

Suppress nerve conduction by blocking voltage gated Na+ channels
Suppress synaptic transmission of nociceptive signals in the dorsal horn of the spinal cord

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3
Q

How do analgesic drugs act to reduce nociception and pain?

A

Activate descending inhibitory controls

Target ion channels upregulated in nerve damage

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4
Q

What is the definition of an opiate?

A

Any substance extracted from opium or of similar structure to those in opium

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5
Q

What is the definition of an opioid?

A

Any agent that acts upon opioid receptors

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6
Q

What mediates supraspinal anti-nociception?

A

Descending pathways from the brainstem

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7
Q

What do brain regions involved in pain project to?

A

Specific brainstem nuclei

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8
Q

What do the neurons of the brainstem nuclei give rise to?

A

Efferent pathways that project to the spinal cord afferent input

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9
Q

What are the regions of the brain involved in supraspinal anti-nociception?

A

Periaqueductal grey = midbrain
Locus ceruleus = pons
Nucleus raphe magnus = medulla

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10
Q

What excites the periaqueductal grey?

A

Electrical stimulation = produces profound analgesia

Endogenous or morphine and related compounds also cause excitation

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11
Q

What is the function of the activated periaqueductal grey neurons?

A

Project to the neucleus raphe magnus and excite serotonergic and enkephalinergic neurons

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12
Q

Where do serotonergic and enkephalinergic neurons project to?

A

The dorsal horn = results in suppression of nociceptive transmission

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13
Q

What is the function of locus ceruleus neurons?

A

Project to dorsal horn and inhibit nociceptive transmission once excited

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14
Q

What mediates opioid action?

A

G protein coupled opioid receptors

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15
Q

Where do G protein coupled opioid receptors signal to?

A

Preferentially signal to Gi/o

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16
Q

What does preferential signalling of opioid receptors to Gi/o produce?

A

Inhibition of opening of voltage activated Ca2+ channels and opening of K+ channels = Gi/o betagamma subunit
Inhibition of adenylate cyclase = Gi/o alpha subunit

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17
Q

What are the different classes of opioid receptors?

A

mu, delta and kappa

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18
Q

Which opioid receptor is responsible for most of the analgesic action of opioids?

A

mu

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19
Q

What are some features of delta opioid receptors?

A

Contributes to analgesia

Activation can be proconvulsant

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20
Q

What are some features of kappa opioid receptors?

A

Contributes to analgesia at the spinal cord and peripheral level
Activation associated with sedation, dysphoria and hallucinations

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21
Q

What are the major adverse side effects of opioids?

A

Addictive, apnoea, orthostatic hypotension

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22
Q

What are some GI side effects of opioids?

A

Nausea, vomiting, constipation and increased intrabiliary pressure

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23
Q

What are some CNS side effects of opioids?

A

Confusion, euphroia, dysphoria, hallucinations, dizziness, myoclonus and hyperalgesia

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24
Q

How do opioids cause apnoea?

A

Blunt the medullary respiratory centre to CO2

Involves mu and delta receptors

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25
Q

How do opioids cause orthostatic hypotension?

A

Reduce sympathetic tone and bradycardia

Cause histamine-evoked vasodilation

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26
Q

How does morphine cause bronchospasm in asthmatics?

A

It causes mast cell degranulation

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27
Q

How do opioids cause GI side effects?

A

Have action on CTZ
Increase smooth muscle tone
Decrease motility via enteric neurons
Involves mu and delta receptors

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28
Q

How do opioid agonists cause analgesia?

A

Mainly through prolonged activation of mu receptors

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29
Q

In what setting is morphine used?

A

Acute severe pain and chronic pain

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30
Q

Where is morphine metabolised?

A

In the liver by glucuronidation at the 3 and 6 positions = yields M3G (inactive) and M6G (retains analgesic activity and excreted by kidney)

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31
Q

What do sustained release preparations of morphine contain?

A

High doses of drugs designed to be released over 12-24hrs

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32
Q

What are some features of diamorphine?

A

More lipophilic than morphine
Enters CNS rapidly when given via IV
Can be used for severe post operative pain

33
Q

What is codeine?

A

Naturally occurring weaker opioid for mild/moderate pain

34
Q

How is codeine metabolised?

A

Hepatic metabolism = demythylation to morphine by CYP2D6 and CYP3A4 accounts mainly for analgesia

35
Q

What are the more potent semi-synthetic derivatives of codeine?

A

Oxycodone and hydrocodone

36
Q

What are some features of codeine?

A

Given orally

Additional anti-diarrhoeal and antitussive effects

37
Q

What are some features of fentanyl?

A

75-100x more potent than morphine
Given IV to provide maintenance anaesthesia
Suitable for transdermal delivery in chronic pain

38
Q

When is pethidine indicated?

A

In acute pain = especially labour

Has rapid onset

39
Q

What are some draw backs of pethidine?

A

Short duration so not suitable for chronic pain
Contraindicated when used with MAO inhibitors
Norpethidine is neurotoxic metabolite = causes seizures

40
Q

What are some examples of opioid agonists?

A

Morphine, diamorphine, codeine, fentanyl, pethidine, buprenophine, tramadol, methadone

41
Q

What are some features of buprenophine?

A

Partial agonist given by injection or sublingually
Useful in chronic pain with patient controlled injection systems
Slow onset but long duration

42
Q

What are some features of tramadol?

A

Weak mu receptor agonist
Potentiates of descending serotonergic and adrenergic systems
Given orally
Avoid in epilepsy

43
Q

What is the action of methodone?

A

Weak mu agonsit of phenylheptlyamine class = also acts on K+ channles, NMDA glutamate receptors and some 5-HT receptors

44
Q

What is methodone used for?

A

Assists in withdrawl from heroin and strong opioids

45
Q

What are some features of methodone?

A

Given orally
Long duration
Useful for chronic pain in terminal cancer

46
Q

What are some examples of opioid antagonists?

A

Naloxone, naltrexone, alvimopan and methylnaltrexone

47
Q

What is naloxone?

A

Competitive antagonist of mu receptor = used to reverse opioid toxicity

48
Q

Why must patients on naloxone be monitored?

A

Naloxone has a very short half life so opioid toxicity may recur

49
Q

What can naloxone trigger in addicts?

A

Acute withdrawl response

50
Q

Why is naloxone sometimes given to newborns?

A

If the newborn has opioid toxicity as a result of mother being given pethidine during labour

51
Q

What are some features of naltrexone?

A

Similar to naloxone but has advantage of oral availability and a much longer half life

52
Q

What are some features of alvimopan and methylnaltrexone?

A

Don’t enter the CNS

Reduce GI effects of surgical and chronic opioid agonist use

53
Q

What effect do NSAIDs have on nociception?

A

Diminish nociceptor sensitisation

54
Q

What kind of pain are NSAIDs used to treat?

A

Mild/moderate inflammatory pain = especially ibuprofen and naproxen

55
Q

What effects do non-selective NSAIDs have?

A

Analgesic, antipyretic and anti-inflammatory

56
Q

What is the action of non-selective NSAIDs?

A

Largely inhibit synthesis and accumulation of prostaglandins by COX 1 and 2

57
Q

What are some examples of non-selective NSAIDs?

A

Aspirin, ibuprofen, naproxen, diclofenac and indomethacin

58
Q

What are some examples of COX 2 selective inhibitor NSAIDs?

A

Etoricoxib, celecoxib and lumiracoxib

59
Q

What is the difference between COX 1 and COX 2?

A

COX 1 is constitutively active but COX 2 is induced locally at sites of inflammation by various cytokines

60
Q

Inhibition of which COX by NSAIDs has the greatest therapeutic benefit?

A

COX 2

61
Q

What effect do NSAIDs have on the activation threshold of peripheral terminals of nociceptors?

A

They suppress the decrease in the activation threshold that is caused by prostaglandins

62
Q

What action do NSAIDs have if they cross the BBB?

A

Suppress the production of pain-producing prostaglandins in the dorsal horn of the spinal cord

63
Q

What effect do NSAIDs have on the leukocytes that produce inflammatory mediators?

A

Decrease leukocyte recruitment

64
Q

Why isn’t paracetamol classed as an NSAID?

A

It lacks anti-inflammatory activity and acts only centrally

65
Q

Why do NSAIDs have limited analgesic efficacy?

A

Multiple pathways cause nociceptor sensitisation

66
Q

Why can long term use of non-selective NSAIDs cause?

A

GI damage

67
Q

Why can nephrotoxicity occur with NSAID use?

A

COX 2 inhibition is constituitively expressed by the kidney

68
Q

What is a side effect of selective COX 2 inhibitors?

A

They are prothrombotic

69
Q

What conditions cause neuropathic pain?

A

Trigeminal neuralgia, diabetic neuropathy, post-herpetic neuralgia and phantom limb pain

70
Q

Why is neuropathic pain difficult to treat?

A

Doesn’t respond to NSAIDs and is relatively insensitive to opioids

71
Q

What are some treatments used for neuropathic pain?

A

Gabapentin and pregabalin,
Amitryptyline, nortryptiline and desipramine
Carbamazepine

72
Q

What are the uses of pregabalin and gabapentin?

A

Anti-epileptics
Gabapentin = migraine prophylaxis
Pregabalin = painful diabetic neuropathy

73
Q

How do gabapentin and pregabalin treat neuropathic pain?

A

Reduce cell surface expression of a subunit of some voltage gated Ca2+ channels which are upregulated by damaged sensory neurons

74
Q

Where do gabapentin and pregabalin decrease neurotransmitters?

A

The central terminals of nociceptive neurons

75
Q

What class of drugs do amitryptiline, nortryptiline and despiramine belong to?

A

Tricyclic antidepressants

76
Q

How do the tricyclic antidepressants treat neuropathic pain?

A

Act centrally by decreasing reuptake of noradrenaline

77
Q

What effect does adding duloxetine or venlafaxine to tricyclic antidepressants have in treating neuropathic pain?

A

Additionally decreases reuptake of 5-HT

78
Q

How does carbamazepine act?

A

Blocks subtypes of voltage activated Na+ channels that are upregulated in damaged nerve cells

79
Q

What is carbamazepine first line for treating?

A

Controlling pain and intensity and frequency of attacks in trigeminal neuralgia

Neurology (48 decks)

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