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MODULE 14 - Patient Support > PHARMACOLOGY - Analgesic Drugs > Flashcards

PHARMACOLOGY - Analgesic Drugs Flashcards

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1
Q

Describe the pain pathway

A

Stimulation of nociceptors generates an action potential which is transmitted along afferent (sensory) neurones to the dorsal horn of the spinal cord, where the information is then transmitted to several regions of the brain to achieve the conscious perception of pain

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2
Q

What is peripheral sensitisation?

A

Peripheral sensitisation is when there is increased stimulation of nociceptors by inflammatory mediators which increases neuronal firing and decreases neuronal firing threshhold, resulting in sensitisation and an amplified pain response being transmitted to the central nervous system (CNS)

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3
Q

What is central sensitisation?

A

Central sensitisation is when the neurones in the dorsal horn of the spinal cord have an increase in neuronal firing and a decrease in neuronal firing threshhold (sensitisation) due to repetitive or prolonged noxious stimulation

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4
Q

What is hyperalgesia?

A

Hyperalgesia is an increased sensitivity to noxious stimuli

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5
Q

What is allodynia?

A

Allodynia is the perception of non-noxious stimuli as noxious

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6
Q

What is the mechanism of action of opioids?

A

Opioids activate μ (mu) κ (kappa) and δ (delta) receptors to decrease neuronal excitability

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7
Q

What are the effects and side affects of opioids?

A

Analgesia
Sedation (can cause excitement in some species)
Euphoria
Nausea/vomiting
Respiratory depression
Antitussive (suppresses cough reflex)
Miosis (Mydriasis in cats)
Decrease gastrointestinal motility
Histamine release

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8
Q

What is a key pharmacokinetic property of opioids?

A

Opioids have poor oral bioavailability due to first pass metabolism

Opioids are most commonly given parenterally

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9
Q

What are the indications for opioids?

A

To reduce moderate to severe acute pain
To provide sedation
To reduce the dose of general anaesthetic required
To treat diarrhoea
To control excessive coughing

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10
Q

What are the contraindications for opioids?

A

Hypoventilation
Increased intracranial pressure (ICP)

Relative contraindications - use lower doses with more careful monitoring

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11
Q

Why are opioids contraindicated in patients with existing hypoventilation?

A

Opioids decrease the sensitivity of the respiratory centre in the brainstem to changes in PaCO2 which can result in hypercapnia. Patients with hypoventilation are already at an increased risk of hypercapnia and this can be exacerbated by opioids

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12
Q

Why are opioids contraindicated in patients with increased intracranial pressure (ICP)?

A

Opioids cause respiratory depression through decreasing the sensitivity of the respiratory centre in the brainstem to changes in PaCO2 which can result in hypercapnia. Hypercapnia triggers cerebral vasodilation to increase blood flow to flush out the excess CO2, however this can further increase intracranial pressure (ICP)

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13
Q

(T/F) Opioids which act on the κ (kappa) receptor have the most profound analgesic effect

A

FALSE. Opioids which act on the μ (mu) receptor have the most profound analgesic effect

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14
Q

What are the three classifications of opioids?

A

Agonists
Partial agonists
Antagonists

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15
Q

Which classification of opioids has the most efficacious analgesic effect?

A

Full μ (mu) agonists

Be aware there are many side effects as these are also mediated by μ

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16
Q

What are partial agonists?

A

Partial agonists are drugs which induce a submaximal response (i.e. lower efficacy)

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17
Q

Why is it ineffective to use an agonist opioid following the administration of a partial agonist opioid?

A

Partial agonist opioid have a very high affinity for opioid receptors, reducing the number of receptors that the full agonist opioid would have to bind to, reducing its desired effect

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18
Q

Give six examples of opioid drugs

A

Methadone
Pethidine
Buprenorphine
Butorphanol
Fentanyl
Tramadol

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19
Q

Give three examples of full μ (mu) agonists

A

Methadone
Pethidine
Fentanyl

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20
Q

(T/F) Pethidine has a long duration of action

A

FALSE. Pethidine has a short duration of action

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21
Q

Give two examples of partial μ (mu) agonists

A

Buprenorphine
Tramadol

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22
Q

Why should pethidine not be given IV?

A

IV pethidine can cause histamine release

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23
Q

Give an example of a partial κ (kappa) agonist

A

Butorphanol

Butorphanol is also a mu antagonist

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24
Q

Which opioid is most commonly used for opioid infusions?

A

Fentanyl

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25
Why is fentanyl the best opioid for infusions?
Fentanyl has a very short duration of action *(approx 30 mins)* which reduces the risk of drug accumulation in the body | Be aware fentanyl is expensive
26
What can be used to reverse opioids?
Opioid antagonists
27
Give an example of an opioid antagonist
Naloxone
28
(T/F) Opioid antagonists are **not** liscenced in food producing animals
TRUE.
29
What is the mechanism of action for NSAIDS?
NSAIDS inhibit the production of proinflammatory mediators prostaglandin and thromboxane A through reversible inhibition of the cyclooxygenase (COX) enzyme
30
What are the two main isoforms of cyclooxygenase (COX)?
Cyclooxygenase-1 (COX-1) Cyclooxygenase-2 (COX-2)
31
Which cyclooxygenase isoform is mainly involved in physiological function?
Cyclooxygenase-1 (COX-1)
32
Which cyclooxygenase isoform is up-regulated in response to inflammatory stimuli?
Cyclooxygenase-2 (COX-2) | Be aware COX-2 is also important for renal perfusion
33
What are the five useful effects of NSAIDS?
Analgesic Anti-pyretic Anti-inflammatory Anti-thrombotic Anti-tumour effects
34
What are the four indicators to administer NSAIDS?
Multimodal acute pain management Long term, chronic pain management Management of inflammatory disorders Management of pro-thrombotic states Management of specific tumours
35
What are the contraindications to NSAID administration?
Gastrointestinal tract disease Acute or chronic renal disease Impaired hepatic function Haemostatic disorders Concurrently treated with steroids Breeding, pregnant or lactating animals Patients with unstable asthma
36
What are the physiological roles of prostaglandins within the gastrointestinal tract?
Within the gastrointestinal tract, prostaglandins inhibit gastric secretion and cause vasodilation to increase blood flow to the stomach and increase mucus production to protect the gastric mucosa
37
Why are NSAIDS contraindicated in patients with gastrointestinal disease?
NSAIDS inhibit cyclooxygenase-1 (COX-1) and thus reduce prostaglandin synthesis which will cause a reduction in blood flow to the gastrointestinal mucosa, resulting in mucosal ischaemia followed by impairment of the protective mucus barrier which will expose the gastric mucosa to the gastric acid causing ulceration
38
Why should NSAIDS always be given with food?
NSAIDS should always be given with food to protect the gastrointestinal mucosa as the contact area of the tablet will receive a high localised concentration of the drug which will increase the risk of ulceration in that area
39
Which cyclooxgenase (COX) isoform is primary involved in physiological renal function?
Cyclooxygenase 2 (COX-2) ## Footnote Important to note that COX-2 specific NSAIDS will not have any less adverse affects on the kidneys
40
What are the physiological roles of prostaglandins in the kidneys?
Renal prostaglandins have a vasodilatory effect and thus increase renal blood flow, improving renal function and excretion. Prostaglandins also provide compensatory vasodilation i.e. maintain blood flow in the presence of vasoconstrictors
41
Why are NSAIDS contraindicated in patients with acute or chronic renal disease?
NSAIDS inhibit cyclooxygenase and thus reduce prostaglandin production which will impair renal blood flow putting these patients at a higher risk of dehydration and acute renal failure
42
Why are NSAIDS contraindicated in patients with impaired hepatic function?
NSAIDS are metabolised by the liver and thus in patients with impaired hepatic function there is an increased risk of drug accumulation and therefore an increased risk of side effects
43
Why are NSAIDS contraindicated in breeding, pregnant or lactating animals?
NSAIDS are teratogenic. Furthermore, NSAIDS inhibit prostaglandin production and since prostaglandins have a role in ovulation, embryo implantation and parturition, this can have adverse effects
44
Why are NSAIDS contraindicated in patients with unstable asthma?
NSAIDs inhibit the cyclooxygenase pathway which can result in a shift to increase arachidonic acid metabolite production via the lipoxygenase pathyway which results in the production of lipoxins and leukotriens. Leukotriens trigger bronchoconstriction which exacerbates asthma
45
Which species is more prone to asthma?
Cats
46
What are the three classifications of NSAIDS?
Non-selective COX inhibitors Preferential COX-2 inhibitors Specific COX-2 inhibitors
47
Which classification of NSAIDS has reduced side effects?
Specific COX-2 inhibitors
48
Give two examples of non-selective COX inhibitors
Flunixin Ketoprofen
49
Give two examples of preferential COX-2 inhibitors
Meloxicam Carprofen
50
Give two examples of specific COX-2 inhibitors
Fibrocoxib Robenacoxib
51
Give an example of a non-COX inhibiting NSAID
Grapiprant
52
What is the mechanism of action for Grapiprant?
Grapiprant is an EP4 prostaglandin receptor antagonist. EP4 receptors mediate pain caused by inflammation, thus inhibition of this receptor prevents the binding of prostaglandin resulting in an analgesic effect
53
Why does grapiprant have fewer adverse effects than other NSAIDS?
Grapiprant does not inhibit the physiological production of prostaglandins resulting in fewer adverse effects
54
What is the mechanism of action for local anaesthetics?
Local anaesthetics prevent the initiation and conduction of action potentials through blocking the voltage-gated sodium channels of nociceptive afferent (sensory) nerve fibres
55
What are the two desirable effects of local anaesthetics?
Analgesia Antiarrhythmic
56
Which local anaesthetic is antiarrhythmic?
Lidocaine
57
Are local anaesthetics weak acids or weak bases?
Local anaesthetics are weak bases
58
Why are inflamed tissues resistant to local anaesthetics?
Inflammatory tissue has an acidic environment, which means the equilibrium will shift to the left and more of the local anaesthetic will exist in its charged form, reducing the quantity of uncharged drug available to cross the cell membrane
59
How does protein binding influence the duration of action of local anaesthetics?
Local anaesthetics have the ability to bind to local structural proteins. The higher degree of protein binding increases the duration of action as there will be a larger reservoir of drug available
60
Why is bicarbonate sometimes added to local anaesthetics?
Bicarbonate increases the pH causing the equilibrium to shift to the right to increase the quantity of local anaesthetic in its unionised form (uncharged) to increase the quantity of drug that can cross the cell membranes and carry out it's effect - increasing speed of onset
61
Why is adrenaline sometimes added to local anaesthetics?
Adrenaline acts on α1 adrenoreceptors on vascular smooth muscle which causes a local vasoconstriction which will limit the blood flow to the area which will decrease the volume of blood that can wash the drug away. This will increase the length of time the local anaesthetic can enter surrounding cells, prolonging it's effect
62
When are harmful side affects to local anaesthetics most likely to occur?
Harmful affects are most likely to occur following an overdose of local anaesthetics or accidental intravenous administration
63
What are the harmful affects that local anaesthetics can have on the central nervous system?
Convulsions Depression Coma Death
64
What are the harmful affects that local anaesthetics can have on the cardiovascular system?
Bradycardia Hypotension
65
What are perineural anaesthetic blocks?
Perineural anaesthetic blocks involve injecting local anaesthetic around the nerves to provide desensitisation to the surrounding structures
66
What kind of perineural anaesthetic block could you do to desensitise the forelimb?
Brachial plexus block
67
What kind of perineural anaesthetic block could you do to desensitise the hindlimb?
Femoral and sciatic block | Good for hindlimb amputations
68
What kind of perineural anaesthetic block could you do to desensitise the digits?
Digital block
69
Why are α2 agonists useful adjunctive drugs when used with local anaesthetics?
α2 adrenoreceptor agonists can be used adjunct to local anaesthetics in perineural blocks to prolong their effect ## Footnote *α2 agonists cause vasoconstriction which will limit the blood flow to the area which will decrease the volume of blood that can wash the drug away which will increase the length of time the local anaesthetic can enter surrounding tissues*
70
What are the two main regions used for local anaesthetic epidurals?
Lumbosacral Coccygeal
71
Which regions of the body are desensitised by a lumbosacral local anaesthetic epidural?
Abdomen *(depending on drug dose)* Hindlimbs Perineum
72
Which regions of the body are desensitised by a coccygeal local anaesthetic epidural?
Perineum Tail
73
When is epidural administration of local anaesthetics contraindicated?
Patients with haemostatic disorders Patients with pyoderma
74
Why is epidural administration of local anaesthetics contraindicated in patients with haemostatic disorders?
If you cause bleeding when introducing the needle into the epidural space, a patient with a haemostatic disorder won't be able to clot which can result in blood accumulating and haematoma formation in the epidural space causing spinal cord compression
75
Why is epidural administration of local anaesthetics contraindicated in patients with pyoderma?
In patients with pyoderma you can introduce bacteria into the epidural space when injecting the local anaesthetic
76
How do you carry out intravenous regional anaesthesia?
Inject the local anaesthetic distal to a tourniquet to prevent the local anaesthetic from spreading into the systemic circulation
77
Which local anaesthetic drug can you use for intravenous regional anaesthesia?
Adrenaline free preparation of lidocaine
78
Which local anaesthetic drug should you NEVER use for intravenous regional anaesthesia?
Bupivicaine
79
When are lidocaine infusions indicated?
Lidocaine infusions are indicated to manage visceral pain
80
Why should you never use lidocaine infusions in cats?
Cats are more prone to drug accumulation and toxicity
81
What is emla cream?
Emla cream is a local anaesthetic cream made by a mix of lidocaine and prilocaine. This is especially useful for patients with very sensitive skin such as rabbits
82
What is oral transmucosal administration?
Oral transmucosal administration is the absorption of a drug through the buccal mucosa into the systemic circulation
83
What is the main benefit of oral transmucosal administration compared to oral administration?
Oral transmucosal administration reduces the impact of first pass metabolism so the bioavailability is greater than it would be following ingestion
84
What is transdermal administration?
Transdermal administration is when lipid soluble, potent drugs are absorbed through the skin into the systemic circulation
85
Give an example of an opioid drug that can be administered transdermally
Fentanyl patch
86
What are the two main advantages of a fentanyl patch?
Allows for opioid treatment at home Long duration of action (three days)
87
What are the four disadvantages of a fentanyl patch?
Takes time to reach peak effect Variable uptake Problems with adhesion of the patch Risk of recreational abuse by owners
88
How long does it take a fentanyl patch to reach it's peak effect in dogs?
24 hours
89
How long does it take a fentanyl patch to reach it's peak effect in cats?
12 hours
90
Which three analgesic drugs are commonly used for combined infusions?
Morphine Lidocaine Ketamine
91
Which factors should you consider when choosing analgesic drugs?
1. Patient pain severity, health status and temperament 2. Procedure invasiveness and possible complications 3. Environment in which the drug is being given *(i.e. at home? at the practice?)* 4. Convenience/practicality and affordability for the client 5. Controlled drug legislation and veterinary medicine register

MODULE 14 - Patient Support (24 decks)

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