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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
Q

What is the purpose of starting pain medication before pain begins (e.g. surgery)?

A

If pain control is pre-meditated, it is more effective (reduces windup)

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26
Q

List two drugs/classes that might be useful as a pre-med for pain

A

Acepromazine

Opioids

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27
Q

Where are endogenous opioids secreted from?

A

pituitary gland and hypothalamus

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28
Q

What are the three types of opioid receptors that have been identified?

A

mu, kappa, delta

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29
Q

What are the functions of the mu-1 opioid receptors

A

analgesia, euphoria (addiction)

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30
Q

What are the functions of mu-2 opioid receptors?

A

respiratory depression (central)

constipation (peripheral)

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31
Q

What are the functions of kappa receptors?

A

analgesia (spinal cord)

dysphoria (central)

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32
Q

What are the functions of delta opioid receptors?

A

analgesia, euphoria, (addiction)

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33
Q

What is the biochemical effect of activation of opioid receptors?

A

reduction in cAMP, closure of Ca++ channels, opening of K+ channels, hyperpolarisation, inhibition of neurotransmission

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34
Q

What is the effect of opioids on inhibitory neurons in the midbrain and dorsal horn?

A

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
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35
Q

Which opioid receptors are associated with supraspinal analgesia?

A

mu (+++)

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36
Q

Which opioid receptors are associated with spinal analgesia?

A

All:

mu (++)

delta (++)

kappa (+)

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37
Q

Which opioid receptors are associated with peripheral analgesia?

A

(++) mu and kappa

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38
Q

Which opioid receptors are associated with respiratory depression

A

mu (+++)

delta (++)

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39
Q

Which opioid receptors are associated with pupil constriction?

A

mu (++)

kappa (+)

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40
Q

Which opioid receptors are associated with reduced gastrointestinal motility?

A

All
mu (++)

delta (++)

kappa (+)

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41
Q

Which opioid receptors are associated with euphoria?

A

mu (+++)

delta (?)

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42
Q

Which opioid receptors are associated with dysphoria?

A

kappa (+++)

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43
Q

Which opioid receptors are associated with sedation?

A

mu and kappa (++)

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44
Q

What are the mechanism of action of morphine?

A

Agonist at mu (& delta)

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45
Q

What are the effects of morphine?

A

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

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46
Q

What are the contraindications/precautions of using morphine

A

CI for head trauma

Caution:
Respiratory depression/dysfunction
Neonates (underdeveloped BBB and liver)
Hepatic dysfunction
Pregnancy (cross placenta)
Hypotension

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47
Q

What is the mechanism of action of methadone

A

Opioid receptor agonist

Inhibits NMDA receptors

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48
Q

Are morphine or methadone long acting or short acting?

A

Short acting

Morphine t1/2 dogs = 1 hr

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49
Q

What is the mechanism of action of buprenorophine

A

Very high affinity partial agonist at mu receptors

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50
Q

Is buprenorphine long or short acting?

A

Long acting (6-8+ hr)

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51
Q

What formulations is buprenorphine available in?

A

Injection, sublingual, transdermal

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52
Q

What is the mechanism of action of butorphanol?

A

Strong kappa agonist

Weak mu antagonist

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53
Q

What are the uses of butorphanol?

A

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

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54
Q

Is butorphanol long or short acting?

A

Short acting

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55
Q

What is the mechanism of action of fentanyl?

A

mu agonist

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56
Q

What is the most common route of administration for fentanyl in dogs?

A

Transdermal patches

57
Q

List two considerations when using fentanyl patches

A
  • best penetration on dog groin, but likely to be chewed off
  • therapeutic doses only reached after 10-12 hours
58
Q

What class of drugs is codeine?

A

Opioid

59
Q

What class of drug is pethidine (meperidine)?

A

Opioid

60
Q

What class of drug is oxymorphone?

A

Opioid

61
Q

What class of drug is hydromorphone?

A

Opioid

62
Q

What class of drug is remifentanil?

A

Opioid

63
Q

What is the use of etorphine?

A

Dart gun (10,000x potency of morphine)

64
Q

What are some special considerations for the use of etorphine?

A

Requires special licence, can be highly fatal, requires antidote

65
Q

What is the use of apomorphine?

A

Emetic only (no pain control)

66
Q

What is the mechanism of action of tramadol?

A

Weak mu agonist

noradrenaline and serotoning reuptake inhibitor

muscarinic M1 agonist

67
Q

What is the mechanism of action of amantadine?

A

NMDA antagonist

M1 agonist

68
Q

What is amantadine used for?

A

Chronic pain

69
Q

What is the mechanism of action of maropitant?

A

Antagonist at NK1 (neurokinin 1) receptor (prevents binding of substance P)

70
Q

What is maropitant used for?

A

Anti-emetic

71
Q

What is the mechanism of action of naloxone?

A

Competitive opioid antagonist (esp mu)

72
Q

What is the use of naloxone?

A

Antidote for opioid overdose

73
Q

What is the use of diprenorphine?

A

Antidote for etorphine

74
Q

Is naloxone long or short acting?

A

Short acting (90 min)

75
Q

Which opioid agonists are the shortest acting (IM administration)?

A

Fentanyl (30-60 min)

Pethidine (90 min)

76
Q

Which opioids are the longest acting (IM administration)?

A

Buprenorphine (6-12 hr)

77
Q

Which opioids have an intermediate duration of action (IM administration)?

A

Butorphanol (2-6 hr)

Methadone (4-6 hr)

Morphine (4-6 hr)

78
Q

Is codeine long or short acting?

A

Intermediate (PO 3-4 h)

79
Q

What are the indication for opioids?

A

Chronic pain
Pre-emptive analgesia for surgery

80
Q

What are some of the potentially beneficial properties of opioids, other than analgesia?

A

Sedative
Antitussive
Emetics
Decreased GIT motility

81
Q

What is the indication for lopermide?

A

Diarrhoea (i.e. antidiarrhoeal)

82
Q

What is the mechanism of action of loperamide?

A

Opioid receptor agonist in the GIT (doesn’t enter blood)

83
Q

Why are opioids considered a useful drug?

A

Highly effective
Variable durations of action
Reversable
Can be used in anaesthesia
Can be used in combination with other agents

84
Q

What is the function of Phospholipase A2?

A

Enzyme: Release of arachadonic acid from membrane phospholipids (following inflammatory stimuli)

85
Q

What are the three pathways for the breakdown of arachadonic acid?

A

1: Cyt P450/Epoxygenase -> ETTs
2: COX (cyclooxygenases) -> Prostanoids (e.g. prostaglandins)
3: LOX (lipoxygenases) -> e.g. leukotrienes

86
Q

What is the mechanism of action of corticosteroids?

A

Inhibits phosopholipase A2

87
Q

What is the mechanism of action of asprin/NSAIDs

A

Inhibits COX1 and/or COX2

88
Q

What is the mechanism of action of zileuton?

A

LOX inhibitor

89
Q

What is the mechanism of action of montelukast/zafirlukast?

A

Leukotriene inhibitors

90
Q

What is a primary difference between COX1 and COX2?

A

COX1: constitutive

COX2: inducable

91
Q

What are the primary functions of constituative prostglandins?

A

Protect gastric mucosa

Platelet aggregation

Increase Renal and GIT blood flow

Macrophage differentiation

92
Q

What are the primary functions of inducable prostaglandins?

A

Recruit inflammatory cells

Sensitize nociceptors

Regulate hypothalamic temperature

93
Q

What is the traditional perception of inhibiting COX 1 or 2 enzymes? Why is this no longer true?

A

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
Q

Name two important metabolites of COX 1

A

Prostaglandin E2

Thromboxane A2

95
Q

What are the normal functions of prostaglandin E2?

A

Vasodilation

Nociceptor sensitization

Increased gastric mucus secretion

Increased gastric acid secretion

Increased bicarbonate secretion

Increased gastric mucosal cell turnover

96
Q

What are the normal functions of Thromboxane A2?

A

Vasoconstriction

Increased platelet activation

97
Q

What are the effects of inhibition of COX1?

A

Inhibition =

Reduced nociception sensitization

Reduced gastric protection (-> perforation, ulcers)

Anticoagulant effect

98
Q

What are three important metabolites of COX2?

A

Prostaglandin E2

Prostacyclin (PGI2)

Lipoxins

99
Q

What are the normal functions of prostacyclin (PGI2)

A

Vasodilation (esp cardiac aa)

Inhibition of platelet aggregation

Increased Na excretion (inhibited reabsorption)

Altered renal blood flow

100
Q

What is the normal function lipoxins

A

Anti-inflammatory effects and modulation of inflammatory response

101
Q

What are the limtations of describing COX selectivity?

A

Assay method (in vitro vs in vivo)

Species differences

102
Q

Which NSAIDs are considered to be selective for COX 2 in dogs?

A

Carprofen
Phenylbutazone
Tolfenamic acid
Meloxicam

103
Q

Name 4 NSAIDs that might be considered for routine use in cats

A

Ketoprofen

Tolenamic acid

Meloxicam

Robenacoxib

104
Q

Name two of the first choice NSAIDs for dogs

A

Carprofen

Meloxicam

105
Q

Would you use Flunixin meglumine in a dog?

A

No -> can cause major GI bleed

106
Q

Name four NSAIDS used in horses

A

Phenylbutazone
Phenylbutazone + ramifenazone
Flunixin meglumine
Meloxicam

107
Q

Would you use Flunixin meglumine in a horse?

A

Yes - good for colic

108
Q

Name 3 NSAIDs for use in ruminants

A

Ketoprofen
Flunixine meglumine
Meloxicam

109
Q

Would you use phenylbutazone in a ruminant?

A

No - drug residues

110
Q

What is the mechanism of action of tepoxalin?

A

Inhibits LOX and COX (dual inhibitor)

111
Q

What are the effects of inhibiting LOX?

A

Thought to be

  • preserve gastric mucosal integrity
  • prevent inflammatory mediators
  • assist in analgesia
112
Q

What are the uses for NSAIDs in veterinary medicine?

A

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
Q

What are some considerations for the GIT when using NSAIDs?

A

Selective COX2 inhibitors have decreased adverse effects

Consider pre-existing GI ulcers

Consider gastroprotectants

114
Q

What are some considerations for the renal system when using NSAIDs?

A

Prostaglandins important in renal dynamics (help maintain normal GFR)

115
Q

What are some considerations when using NSAIDs in cardiac patients?

A

Cardiac patients:
NSAIDs decrease renal blood flow
ACE inhibitors vasodilate efferent arteriole
Diuretics decrease blood volume and renal perfusion
(Triple whammy)

116
Q

What are some considerations regarding the hepatic system when using NSAIDs?

A

Intrinisic (dose-dependent) toxicity (OD)
Idiosyncratic (dose-independent) toxicity (label dose)
Onset of clinical signs variable (days - weeks)

117
Q

What are some considerations regaring the skeletal system when using NSAIDs?

A

Chondroprotective???
May retard early fracture repair
Should be avoided in very young animals

118
Q

What are some other agents that may assist in analgesia and inflammatory disease?

A

Local anaesthetics

Chondroprotectants

DMARDS (Disease-modifying antirheumatic drugs)

119
Q

What are some adjunct therapies used as chondroprotective agents?

A

Polysuphated glucosaminoglycans

Pentosan polysulphate

Sodium hyaluronate

Glucosamine and chondroitin sulphate

Glucosamine (??? nutraceutical)

120
Q

What is the use of adequan?

A

IM for joint infection in horses

121
Q

What is the mechanism of action of Adequan?

A

Enhance cartilage regeneration and inhibit metalloprotease enzymes that damage cartilage

122
Q

What is the use of cartrophen (pentosan polysulfate)?

A

Injection or PO for arthritis/degenerative joint disease in dogs and horses

123
Q

What is the mechanism of action of Cartrophen (pentosan polysulfate)?

A

Modulates cytokines

Preserves proteoglycans

Stimulate hyaluronic acid synthesis

124
Q

What are corticosteroids?

A

Cholesterol based hormones

125
Q

What is a primary function of glucocorticoids?

A

Glucose metabolism

126
Q

What is a primary function of mineralocorticoids?

A

Ion metabolism (Na, K, Cl)

127
Q

What are the effects of corticosteroids on inflammation?

A

Stabilise cell membranes and prevent release of arachidonic acid and histamines (disruption of the inflammatory mediator pathways)

128
Q

What are the effects of glucocorticoids on immune function?

A

Immunosuppression

Cytotoxic to T lymphocytes at high concentration

Cause a reduction in neutrophil movement

Reduction in dendritic (antigen presenting) cells

129
Q

What are some of the uses of corticosteroids?

A

Control over some allergies (e.g. asthma)

Reduce inflammation and excessive scarring

Control immune-mediated disease

130
Q

What are some negative issues with use of glucocorticosteroids?

A
  • delay healing
  • increase susceptibility of infections
  • may activate latent infections
  • antagonise insuline
  • no analgesia
    NB: adverse side effects related to dose/frequency
131
Q

What are two short-acting glucocorticoids?

A

Cortisone

Hydrocortisone

132
Q

What are three intermediate acting glucocorticoids?

A

Prednisone/Prednisolone

Methylprednisolone

Triamcinalone

133
Q

What are three long-acting glucocortcoids?

A

Flumethasone

Dexamethsone

Betamethasone

134
Q

What are the potential routs of administration of glucocorticoids?

A 
Oral
Injectable (IV, IM, SC, Intra-articular, intralesional)

Topical (eye, skin, ears)

Inhalation

135
Q

Can glucocorticoids and NSAIDs be given simultaneously?

A

No

136
Q

What are the recommendations for chronic dosing of glucocorticoids?

A

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
Q

Why is it important to taper off the dose of glucocorticoids?

A

Body’s natural cortisol will be depressed

Prevent iatrogenic hyperadrenocorticism

138
Q

What are some examples of DMARDs?

A

Disease modifying anti rhumetic drugs*

TNFalpha inhibitors

Methotrexate

Cyclosporine

Slphasalazine

* especially used in human medicine

Pharmacology (12 decks)

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