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Analgesic Drugs Flashcards

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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
How do opioids cause orthostatic hypotension?
Reduce sympathetic tone and bradycardia | Cause histamine-evoked vasodilation
26
How does morphine cause bronchospasm in asthmatics?
It causes mast cell degranulation
27
How do opioids cause GI side effects?
Have action on CTZ Increase smooth muscle tone Decrease motility via enteric neurons Involves mu and delta receptors
28
How do opioid agonists cause analgesia?
Mainly through prolonged activation of mu receptors
29
In what setting is morphine used?
Acute severe pain and chronic pain
30
Where is morphine metabolised?
In the liver by glucuronidation at the 3 and 6 positions = yields M3G (inactive) and M6G (retains analgesic activity and excreted by kidney)
31
What do sustained release preparations of morphine contain?
High doses of drugs designed to be released over 12-24hrs
32
What are some features of diamorphine?
More lipophilic than morphine Enters CNS rapidly when given via IV Can be used for severe post operative pain
33
What is codeine?
Naturally occurring weaker opioid for mild/moderate pain
34
How is codeine metabolised?
Hepatic metabolism = demythylation to morphine by CYP2D6 and CYP3A4 accounts mainly for analgesia
35
What are the more potent semi-synthetic derivatives of codeine?
Oxycodone and hydrocodone
36
What are some features of codeine?
Given orally | Additional anti-diarrhoeal and antitussive effects
37
What are some features of fentanyl?
75-100x more potent than morphine Given IV to provide maintenance anaesthesia Suitable for transdermal delivery in chronic pain
38
When is pethidine indicated?
In acute pain = especially labour | Has rapid onset
39
What are some draw backs of pethidine?
Short duration so not suitable for chronic pain Contraindicated when used with MAO inhibitors Norpethidine is neurotoxic metabolite = causes seizures
40
What are some examples of opioid agonists?
Morphine, diamorphine, codeine, fentanyl, pethidine, buprenophine, tramadol, methadone
41
What are some features of buprenophine?
Partial agonist given by injection or sublingually Useful in chronic pain with patient controlled injection systems Slow onset but long duration
42
What are some features of tramadol?
Weak mu receptor agonist Potentiates of descending serotonergic and adrenergic systems Given orally Avoid in epilepsy
43
What is the action of methodone?
Weak mu agonsit of phenylheptlyamine class = also acts on K+ channles, NMDA glutamate receptors and some 5-HT receptors
44
What is methodone used for?
Assists in withdrawl from heroin and strong opioids
45
What are some features of methodone?
Given orally Long duration Useful for chronic pain in terminal cancer
46
What are some examples of opioid antagonists?
Naloxone, naltrexone, alvimopan and methylnaltrexone
47
What is naloxone?
Competitive antagonist of mu receptor = used to reverse opioid toxicity
48
Why must patients on naloxone be monitored?
Naloxone has a very short half life so opioid toxicity may recur
49
What can naloxone trigger in addicts?
Acute withdrawl response
50
Why is naloxone sometimes given to newborns?
If the newborn has opioid toxicity as a result of mother being given pethidine during labour
51
What are some features of naltrexone?
Similar to naloxone but has advantage of oral availability and a much longer half life
52
What are some features of alvimopan and methylnaltrexone?
Don't enter the CNS | Reduce GI effects of surgical and chronic opioid agonist use
53
What effect do NSAIDs have on nociception?
Diminish nociceptor sensitisation
54
What kind of pain are NSAIDs used to treat?
Mild/moderate inflammatory pain = especially ibuprofen and naproxen
55
What effects do non-selective NSAIDs have?
Analgesic, antipyretic and anti-inflammatory
56
What is the action of non-selective NSAIDs?
Largely inhibit synthesis and accumulation of prostaglandins by COX 1 and 2
57
What are some examples of non-selective NSAIDs?
Aspirin, ibuprofen, naproxen, diclofenac and indomethacin
58
What are some examples of COX 2 selective inhibitor NSAIDs?
Etoricoxib, celecoxib and lumiracoxib
59
What is the difference between COX 1 and COX 2?
COX 1 is constitutively active but COX 2 is induced locally at sites of inflammation by various cytokines
60
Inhibition of which COX by NSAIDs has the greatest therapeutic benefit?
COX 2
61
What effect do NSAIDs have on the activation threshold of peripheral terminals of nociceptors?
They suppress the decrease in the activation threshold that is caused by prostaglandins
62
What action do NSAIDs have if they cross the BBB?
Suppress the production of pain-producing prostaglandins in the dorsal horn of the spinal cord
63
What effect do NSAIDs have on the leukocytes that produce inflammatory mediators?
Decrease leukocyte recruitment
64
Why isn't paracetamol classed as an NSAID?
It lacks anti-inflammatory activity and acts only centrally
65
Why do NSAIDs have limited analgesic efficacy?
Multiple pathways cause nociceptor sensitisation
66
Why can long term use of non-selective NSAIDs cause?
GI damage
67
Why can nephrotoxicity occur with NSAID use?
COX 2 inhibition is constituitively expressed by the kidney
68
What is a side effect of selective COX 2 inhibitors?
They are prothrombotic
69
What conditions cause neuropathic pain?
Trigeminal neuralgia, diabetic neuropathy, post-herpetic neuralgia and phantom limb pain
70
Why is neuropathic pain difficult to treat?
Doesn't respond to NSAIDs and is relatively insensitive to opioids
71
What are some treatments used for neuropathic pain?
Gabapentin and pregabalin, Amitryptyline, nortryptiline and desipramine Carbamazepine
72
What are the uses of pregabalin and gabapentin?
Anti-epileptics Gabapentin = migraine prophylaxis Pregabalin = painful diabetic neuropathy
73
How do gabapentin and pregabalin treat neuropathic pain?
Reduce cell surface expression of a subunit of some voltage gated Ca2+ channels which are upregulated by damaged sensory neurons
74
Where do gabapentin and pregabalin decrease neurotransmitters?
The central terminals of nociceptive neurons
75
What class of drugs do amitryptiline, nortryptiline and despiramine belong to?
Tricyclic antidepressants
76
How do the tricyclic antidepressants treat neuropathic pain?
Act centrally by decreasing reuptake of noradrenaline
77
What effect does adding duloxetine or venlafaxine to tricyclic antidepressants have in treating neuropathic pain?
Additionally decreases reuptake of 5-HT
78
How does carbamazepine act?
Blocks subtypes of voltage activated Na+ channels that are upregulated in damaged nerve cells
79
What is carbamazepine first line for treating?
Controlling pain and intensity and frequency of attacks in trigeminal neuralgia

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