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Pharmacology > Pharmacology of pain > Flashcards

Pharmacology of pain Flashcards

1
Q

What is pain?

A

An unpleasant feeling conveyed to the brain by sensory neurons, either from actual or potential perceived injury or discomfort

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2
Q

Describe the structure of nociceptors

A

Free, non-myelinated nerve endings of afferent neurons

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3
Q

What is the function of nociceptors?

A

Specific for the sensation of pain

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4
Q

What modalities stimulate a nociceptor?

A

Noxious stimuli: temperature, mechanical, or chemical

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5
Q

What is the “inflammatory soup”?

A

A mix of inflammatory mediators which are released during tissue injury and potentiate the sensation of pain

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6
Q

What are the mediators involved in the “inflammatory soup”?

A

Serotonin, bradykinin, prostaglanding, K+

Mast cells: histamine and bradykinin

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7
Q

What is the result of the “inflammatory soup”?

A

Hyperalgesia (increased perception of pain)

OR

Allodynia (something that shouldn’t hurt but does)

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8
Q

What are the two types of nerve fibres involved in pain?

A

Type A-delta

Type C

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9
Q

Describe Type A-delta nociceptive fibres

A

myelinated nerve fibres that transmit sharp/fast/localised pain

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10
Q

Describe C type nociceptive fibres

A

Unmyelinated fibres that transmit slow/dull/diffuse pain

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11
Q

Which type of nerve fibres are present in visceral organs?

A

Type C

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12
Q

What is the clinical relevance of having two types of pain receptors?

A

Multimodal pain relief is usually more effective

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13
Q

Which neurotransmitters are involved in pain transmission?

A

Glutamate, substance P, calcitonin gene-related peptide

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14
Q

Which brain region is associated in the perception of pain?

A

Thalamus

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15
Q

Which brain region is involved in the localisation of pain?

A

Somatosensory cortex

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16
Q

Which brain region is involved in behavioural and emotional responses to pain?

A

Hypothalamus and limbic system

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17
Q

What is “dorsal horn windup”?

A

Windup = amplification of chronic pain

(at each synapse in the neuronal pathway, there is opportunity for amplification of the pain signal, in particular the dorsal horn of the spinal cord?

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18
Q

What is the clinical relevance of “wind-up”

A

Wind up is hard to treat, so it is important to treat pain hard and fast

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19
Q

Which endogenous substance are involved in limiting pain?

A

Endogenous opioids

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20
Q

How do endogenous opioids work?

A

Endogenous opioids act to inhbit the release of substance P from nociceptor axon terminals

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21
Q

What is the gate cell theory?

A

Stimulation of afferent fibres inhibits nociceptive transmission in the dorsal horn of the spinal cord.

Gate cell inter-neurons inhibit C fibre transmission

Pain in one place can reduce pain in another place

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22
Q

Name five drug classes that can be used in the pharmacology of analgesia

A

alpha 2 agonists (central)

NMDA antagonists (central

opioids

NSAIDs

Local anaesthetics

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23
Q

What are the signs of pain in animals?

A

Withdrawal

Altered activity level

Decreased appetitite

Agression, fear

vocalisation

species-specific signs

pain scores

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24
Q

Why is pain treatment important?

A

Reduced suffering

Improved healing/reduced healing time

Increased food intake and prevention of catabolism

Stops self mutilation

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25
What is the purpose of starting pain medication before pain begins (e.g. surgery)?
If pain control is pre-meditated, it is more effective (reduces windup)
26
List two drugs/classes that might be useful as a pre-med for pain
Acepromazine Opioids
27
Where are endogenous opioids secreted from?
pituitary gland and hypothalamus
28
What are the three types of opioid receptors that have been identified?
mu, kappa, delta
29
What are the functions of the mu-1 opioid receptors
analgesia, euphoria (addiction)
30
What are the functions of mu-2 opioid receptors?
respiratory depression (central) constipation (peripheral)
31
What are the functions of kappa receptors?
analgesia (spinal cord) dysphoria (central)
32
What are the functions of delta opioid receptors?
analgesia, euphoria, (addiction)
33
What is the biochemical effect of activation of opioid receptors?
reduction in cAMP, closure of Ca++ channels, opening of K+ channels, hyperpolarisation, inhibition of neurotransmission
34
What is the effect of opioids on inhibitory neurons in the midbrain and dorsal horn?
Opioids -\> inhibit GABA release in the PAG (periaquaductal grey matter) -\> potientiate inhibitory neurons - \> inhibit release of substance P -\> decrease pain transmission - \> open K+ channels in nociceptor nerve endings -\> hyperpolarisation
35
Which opioid receptors are associated with supraspinal analgesia?
mu (+++)
36
Which opioid receptors are associated with spinal analgesia?
All: mu (++) delta (++) kappa (+)
37
Which opioid receptors are associated with peripheral analgesia?
(++) mu and kappa
38
Which opioid receptors are associated with respiratory depression
mu (+++) delta (++)
39
Which opioid receptors are associated with pupil constriction?
mu (++) kappa (+)
40
Which opioid receptors are associated with reduced gastrointestinal motility?
All mu (++) delta (++) kappa (+)
41
Which opioid receptors are associated with euphoria?
mu (+++) delta (?)
42
Which opioid receptors are associated with dysphoria?
kappa (+++)
43
Which opioid receptors are associated with sedation?
mu and kappa (++)
44
What are the mechanism of action of morphine?
Agonist at mu (& delta)
45
What are the effects of morphine?
Bradycardia Respiratory depression Antitussive (decreased coughing) Emesis (stimulates chemosensory trigger zone) Decrease GIT Species dependent effects: Dogs, humans: CNS depression + miosis Other spp: Excititation and mydriasis
46
What are the contraindications/precautions of using morphine
CI for head trauma Caution: Respiratory depression/dysfunction Neonates (underdeveloped BBB and liver) Hepatic dysfunction Pregnancy (cross placenta) Hypotension
47
What is the mechanism of action of methadone
Opioid receptor agonist Inhibits NMDA receptors
48
Are morphine or methadone long acting or short acting?
Short acting Morphine t1/2 dogs = 1 hr
49
What is the mechanism of action of buprenorophine
Very high affinity partial agonist at mu receptors
50
Is buprenorphine long or short acting?
Long acting (6-8+ hr)
51
What formulations is buprenorphine available in?
Injection, sublingual, transdermal
52
What is the mechanism of action of butorphanol?
Strong kappa agonist Weak mu antagonist
53
What are the uses of butorphanol?
Effective visceral analgesic Good antitussive and premed in combination with other drugs Mild sedative in dogs (not cats) Sedative and analgesic in horses and cattle
54
Is butorphanol long or short acting?
Short acting
55
What is the mechanism of action of fentanyl?
mu agonist
56
What is the most common route of administration for fentanyl in dogs?
Transdermal patches
57
List two considerations when using fentanyl patches
- best penetration on dog groin, but likely to be chewed off - therapeutic doses only reached after 10-12 hours
58
What class of drugs is codeine?
Opioid
59
What class of drug is pethidine (meperidine)?
Opioid
60
What class of drug is oxymorphone?
Opioid
61
What class of drug is hydromorphone?
Opioid
62
What class of drug is remifentanil?
Opioid
63
What is the use of etorphine?
Dart gun (10,000x potency of morphine)
64
What are some special considerations for the use of etorphine?
Requires special licence, can be highly fatal, requires antidote
65
What is the use of apomorphine?
Emetic only (no pain control)
66
What is the mechanism of action of tramadol?
Weak mu agonist noradrenaline and serotoning reuptake inhibitor muscarinic M1 agonist
67
What is the mechanism of action of amantadine?
NMDA antagonist M1 agonist
68
What is amantadine used for?
Chronic pain
69
What is the mechanism of action of maropitant?
Antagonist at NK1 (neurokinin 1) receptor (prevents binding of substance P)
70
What is maropitant used for?
Anti-emetic
71
What is the mechanism of action of naloxone?
Competitive opioid antagonist (esp mu)
72
What is the use of naloxone?
Antidote for opioid overdose
73
What is the use of diprenorphine?
Antidote for etorphine
74
Is naloxone long or short acting?
Short acting (90 min)
75
Which opioid agonists are the shortest acting (IM administration)?
Fentanyl (30-60 min) Pethidine (90 min)
76
Which opioids are the longest acting (IM administration)?
Buprenorphine (6-12 hr)
77
Which opioids have an intermediate duration of action (IM administration)?
Butorphanol (2-6 hr) Methadone (4-6 hr) Morphine (4-6 hr)
78
Is codeine long or short acting?
Intermediate (PO 3-4 h)
79
What are the indication for opioids?
Chronic pain Pre-emptive analgesia for surgery
80
What are some of the potentially beneficial properties of opioids, other than analgesia?
Sedative Antitussive Emetics Decreased GIT motility
81
What is the indication for lopermide?
Diarrhoea (i.e. antidiarrhoeal)
82
What is the mechanism of action of loperamide?
Opioid receptor agonist in the GIT (doesn't enter blood)
83
Why are opioids considered a useful drug?
Highly effective Variable durations of action Reversable Can be used in anaesthesia Can be used in combination with other agents
84
What is the function of Phospholipase A2?
Enzyme: Release of arachadonic acid from membrane phospholipids (following inflammatory stimuli)
85
What are the three pathways for the breakdown of arachadonic acid?
1: Cyt P450/Epoxygenase -\> ETTs 2: COX (cyclooxygenases) -\> Prostanoids (e.g. prostaglandins) 3: LOX (lipoxygenases) -\> e.g. leukotrienes
86
What is the mechanism of action of corticosteroids?
Inhibits phosopholipase A2
87
What is the mechanism of action of asprin/NSAIDs
Inhibits COX1 and/or COX2
88
What is the mechanism of action of zileuton?
LOX inhibitor
89
What is the mechanism of action of montelukast/zafirlukast?
Leukotriene inhibitors
90
What is a primary difference between COX1 and COX2?
COX1: constitutive COX2: inducable
91
What are the primary functions of constituative prostglandins?
Protect gastric mucosa Platelet aggregation Increase Renal and GIT blood flow Macrophage differentiation
92
What are the primary functions of inducable prostaglandins?
Recruit inflammatory cells Sensitize nociceptors Regulate hypothalamic temperature
93
What is the traditional perception of inhibiting COX 1 or 2 enzymes? Why is this no longer true?
Originally thought better to specifically inhibit COX 2 (inducable), as COX 1 has normal homeostatic/protective functions In reality not this simple - specific inhibition of COX2 may be less effective & have procoagulant effects
94
Name two important metabolites of COX 1
Prostaglandin E2 Thromboxane A2
95
What are the normal functions of prostaglandin E2?
Vasodilation Nociceptor sensitization Increased gastric mucus secretion Increased gastric acid secretion Increased bicarbonate secretion Increased gastric mucosal cell turnover
96
What are the normal functions of Thromboxane A2?
Vasoconstriction Increased platelet activation
97
What are the effects of inhibition of COX1?
Inhibition = Reduced nociception sensitization Reduced gastric protection (-\> perforation, ulcers) Anticoagulant effect
98
What are three important metabolites of COX2?
Prostaglandin E2 Prostacyclin (PGI2) Lipoxins
99
What are the normal functions of prostacyclin (PGI2)
Vasodilation (esp cardiac aa) Inhibition of platelet aggregation Increased Na excretion (inhibited reabsorption) Altered renal blood flow
100
What is the normal function lipoxins
Anti-inflammatory effects and modulation of inflammatory response
101
What are the limtations of describing COX selectivity?
Assay method (in vitro vs in vivo) Species differences
102
Which NSAIDs are considered to be selective for COX 2 in dogs?
Carprofen Phenylbutazone Tolfenamic acid Meloxicam
103
Name 4 NSAIDs that might be considered for routine use in cats
Ketoprofen Tolenamic acid Meloxicam Robenacoxib
104
Name two of the first choice NSAIDs for dogs
Carprofen Meloxicam
105
Would you use Flunixin meglumine in a dog?
No -\> can cause major GI bleed
106
Name four NSAIDS used in horses
Phenylbutazone Phenylbutazone + ramifenazone Flunixin meglumine Meloxicam
107
Would you use Flunixin meglumine in a horse?
Yes - good for colic
108
Name 3 NSAIDs for use in ruminants
Ketoprofen Flunixine meglumine Meloxicam
109
Would you use phenylbutazone in a ruminant?
No - drug residues
110
What is the mechanism of action of tepoxalin?
Inhibits LOX and COX (dual inhibitor)
111
What are the effects of inhibiting LOX?
Thought to be - preserve gastric mucosal integrity - prevent inflammatory mediators - assist in analgesia
112
What are the uses for NSAIDs in veterinary medicine?
Pre-emptive analgesia for surgery/painful procedures Analgesioa for acute pain (trauma/injury) Treatment of chronic pain Treatment for some neoplasia (COX2 -\> new bv) | (care: can decrease renal blood flow)
113
What are some considerations for the GIT when using NSAIDs?
Selective COX2 inhibitors have decreased adverse effects Consider pre-existing GI ulcers Consider gastroprotectants
114
What are some considerations for the renal system when using NSAIDs?
Prostaglandins important in renal dynamics (help maintain normal GFR)
115
What are some considerations when using NSAIDs in cardiac patients?
Cardiac patients: NSAIDs decrease renal blood flow ACE inhibitors vasodilate efferent arteriole Diuretics decrease blood volume and renal perfusion (Triple whammy)
116
What are some considerations regarding the hepatic system when using NSAIDs?
Intrinisic (dose-dependent) toxicity (OD) Idiosyncratic (dose-independent) toxicity (label dose) Onset of clinical signs variable (days - weeks)
117
What are some considerations regaring the skeletal system when using NSAIDs?
Chondroprotective??? May retard early fracture repair Should be avoided in very young animals
118
What are some other agents that may assist in analgesia and inflammatory disease?
Local anaesthetics Chondroprotectants DMARDS (Disease-modifying antirheumatic drugs)
119
What are some adjunct therapies used as chondroprotective agents?
Polysuphated glucosaminoglycans Pentosan polysulphate Sodium hyaluronate Glucosamine and chondroitin sulphate Glucosamine (??? nutraceutical)
120
What is the use of adequan?
IM for joint infection in horses
121
What is the mechanism of action of Adequan?
Enhance cartilage regeneration and inhibit metalloprotease enzymes that damage cartilage
122
What is the use of cartrophen (pentosan polysulfate)?
Injection or PO for arthritis/degenerative joint disease in dogs and horses
123
What is the mechanism of action of Cartrophen (pentosan polysulfate)?
Modulates cytokines Preserves proteoglycans Stimulate hyaluronic acid synthesis
124
What are corticosteroids?
Cholesterol based hormones
125
What is a primary function of glucocorticoids?
Glucose metabolism
126
What is a primary function of mineralocorticoids?
Ion metabolism (Na, K, Cl)
127
What are the effects of corticosteroids on inflammation?
Stabilise cell membranes and prevent release of arachidonic acid and histamines (disruption of the inflammatory mediator pathways)
128
What are the effects of glucocorticoids on immune function?
Immunosuppression Cytotoxic to T lymphocytes at high concentration Cause a reduction in neutrophil movement Reduction in dendritic (antigen presenting) cells
129
What are some of the uses of corticosteroids?
Control over some allergies (e.g. asthma) Reduce inflammation and excessive scarring Control immune-mediated disease
130
What are some negative issues with use of glucocorticosteroids?
- delay healing - increase susceptibility of infections - may activate latent infections - antagonise insuline - no analgesia NB: adverse side effects related to dose/frequency
131
What are two short-acting glucocorticoids?
Cortisone Hydrocortisone
132
What are three intermediate acting glucocorticoids?
Prednisone/Prednisolone Methylprednisolone Triamcinalone
133
What are three long-acting glucocortcoids?
Flumethasone Dexamethsone Betamethasone
134
What are the potential routs of administration of glucocorticoids?
``` Oral Injectable (IV, IM, SC, Intra-articular, intralesional) ``` Topical (eye, skin, ears) Inhalation
135
Can glucocorticoids and NSAIDs be given simultaneously?
No
136
What are the recommendations for chronic dosing of glucocorticoids?
Inital induction of 5-7 days Decrease dose frequency to maintenance daily dose When treatment is over, reduce daily dose, than decrease frequency to ever other day Should be administed for the shortest reasonable period of time
137
Why is it important to taper off the dose of glucocorticoids?
Body's natural cortisol will be depressed Prevent iatrogenic hyperadrenocorticism
138
What are some examples of DMARDs?
Disease modifying anti rhumetic drugs\* TNFalpha inhibitors Methotrexate Cyclosporine Slphasalazine \* especially used in human medicine

Pharmacology (12 decks)

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