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Anaesthetic FRCA Primary - eLFH Pharmacology > eLFH - Adrenoreceptor Antagonists > Flashcards

eLFH - Adrenoreceptor Antagonists Flashcards

1
Q

Intracellular pathways following adrenoreceptor stimulation

A
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2
Q

Types of adrenergic receptor

A

Alpha and Beta

Subtypes of Alpha 1 and Alpha 2, and Beta 1 and Beta 2 (and Beta 3)

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3
Q

Alpha 1 adrenoreceptor G protein

A

Gq

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4
Q

Effects of Alpha 1 adrenoreceptor stimulation

A

Vascular smooth muscle contraction

Bladder / Uterine contraction

Iris contraction

Intestinal relaxation

Glycogenolysis

Decreased insulin and glucagon secretion

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5
Q

Alpha 2 adrenoreceptor G protein

A

Gi

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6
Q

Effects of Alpha 2 adrenoreceptor stimulation

A

Reduced Noradrenaline release

Vasodilatation of arterioles

Venoconstriction of veins and coronary arteries

Platelet aggregation

Intestinal relaxation

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7
Q

Beta 1, 2 and 3 adrenoreceptor G protein

A

Gs

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8
Q

Effects of Beta 1 adrenoreceptor stimulation

A

Increased HR

Positive inotropy

Increased renin secretion

Lipolysis

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9
Q

Effects of Beta 2 adrenoreceptor stimulation

A

Smooth muscle relaxation including vascular, bronchioles, intestinal, bladder and uterine

Glycogenolysis

Increased insulin and glucagon secretion

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10
Q

Effects of Beta 3 adrenoreceptor stimulation

A

Lipolysis

Thermogenesis (brown fat)

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11
Q

Types of alpha adrenoreceptor antagonists

A

Selective alpha 1 antagonists

Non selective alpha antagonists

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12
Q

Examples of selective alpha 1 antagonists

A

Doxazosin

Prazosin

Terazosin

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13
Q

Use of selective alpha 1 antagonists

A

Essential HTN

Phaeochromocytoma

CCF

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14
Q

Side effects of selective alpha 1 antagonists

A

Postural hypotension (after first doses especially)

Syncope

Increased micturition frequency (bladder muscle relaxation)

Drowsiness

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15
Q

Side effects of non selective alpha antagonists

A

Same as selective alpha 1 side effects + effects of blocking alpha 2 as well

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16
Q

Examples of non selective alpha antagonists

A

Phentolamine

Phenoxybenzamine

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17
Q

Phentolamine mechanism of action

A

Antagonist of alpha 1 and alpha 2 adreno receptors

3x more affinity for alpha 1

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18
Q

Phentolamine route of administration

A

IV

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19
Q

Effects of phentolamine

A

Vasodilatation via alpha 1 antagonism

Increased HR and therefore cardiac output due to increased noradrenaline release via alpha 2 antagonism

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20
Q

Use of phentolamine

A

Hypertensive crisis due to excessive sympathetic activity, MAOi reactions or intra-operative phaeochromocytoma removal

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21
Q

Side effects of phentolamine

A

Nasal congestion - vasodilatation of nasal vessels

Sulphites in preparation can cause bronchospasm in asthmatics

Hypoglycaemia due to raised insulin

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22
Q

Phenoxybenzamine pharmacokinetics

A

Longer acting alpha adrenoreceptor antagonist

More affinity for alpha 1 receptors

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23
Q

Phenoxybenzamine route of administration

A

PO

IV

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24
Q

Use of phenoxybenzamine

A

Pre-op treatment of phaeochromocytoma and hypertensive crisis

25
Q

Phenoxybenzamine mechanism of action

A

Irreversible blockade of alpha adrenoreceptors

Inhibits catecholamine uptake into neurones

26
Q

Phenoxybenzamine duration of action

A

Half life 24 hours

Lasts until new receptors are produced

27
Q

Side effects of phenoxybenzamine

A

Reflex tachycardia due to alpha 2 antagonism

Miosis

Sedation

28
Q

Classification of Beta adrenoreceptor antagonists

A

Non selective action

Selective Beta 1 antagonism (‘cardio selective’)

Can also be classified according to generation - 3rd generation are vasodilatory via alpha 1 antagonism or nitric oxide release

29
Q

Non selective beta receptor antagonist examples

A

Carvedilol

Labetalol

Propranolol

Timolol

Sotalol

30
Q

Selective beta 1 antagonist examples

A

Atenolol

Metoprolol

Esmolol

Bisoprolol

Nebivolol

31
Q

Effects of beta adrenoreceptor antagonists

A

Negative inotropy and chronotropy

Reduces sinoatrial node automaticity

Decreases atrioventricular node conduction

Increases time in diastole increasing O2 supply to myocardium

32
Q

Indications for beta adrenoreceptor antagonist use

A

IHD - angina and post MI

Arrhythmias

Congestive heart failure

Phaeochromocytoma (in conjunction with alpha blockers)

Thyrotoxicosis (propranolol)

Migraine prophylaxis

Glaucoma

33
Q

Side effects of beta adrenoreceptor antagonists

A

Cool extremities with reduced peripheral circulation

Bronchospasm in susceptible people

Masks hypoglycaemia symptoms

Some cross blood brain barrier

Urinary retention

Increased uterine tone

34
Q

Effects of beta adrenoreceptor antagonists when they cross blood brain barrier

A

Hallucinations

Nightmares

Depression

35
Q

Intrinsic sympathomimetic activity definition

A

A property that some beta blockers possess

Partial agonism of beta adrenoreceptors if endogenous catecholamine levels are low - sympathomimetic effects

If endogenous catecholamine levels are high then acts as antagonist of beta receptors

36
Q

Examples of beta receptor antagonists with intrinsic sympathomimetic activity

A

Timolol

Acebutolol

Pindolol

37
Q

Intended benefits of beta blockers with intrinsic sympathomimetic activity

A

Theoretically less likely to cause bradycardia but not been shown to be beneficial post MI

38
Q

Use of beta receptor antagonists in cardiac failure

A

Some beta blockers shown to reduce hospital admissions and improve long term survival

Mechanism of action is poorly understood and no clear classification of beta blockers are beneficial - can be non-selective or beta 1 selective, and of different generations (other method of classifying beta blockers)

39
Q

Examples of beta adrenoreceptor antagonists that are beneficial in heart failure

A

Carvedilol (most successful)

Bisoprolol

Metoprolol

40
Q

Possible mechanisms of action of beta blockers in providing benefit to cardiac failure patients

A

Reduction in harmful cardiac remodelling - blocks excessive chronic sympathetic stimulation of the heart

Reduction in renin secretion - reduces heart O2 demand by lowering extracellular volume

41
Q

Phaeochromocytoma definition

A

Tumour of chromaffin cells in adrenal medulla
(or in other paraganglia of sympathetic nervous system)

Increased circulating catecholamines (norad, adrenaline, dopamine)

Rare

42
Q

Symptoms of phaeochromocytoma

A

Noradrenaline - HTN refractory to treatment

Adrenaline and Dopamine - episodic panic attacks and palpitations

43
Q

Management of phaeochromocytoma

A

Surgical

Pharmacological treatment pre-op

44
Q

Goals of pharmacological treatment pre-op for phaeochromocytoma

A

Good BP control

Treatment of significant arrhythmias

Restoration of circulating blood volume

45
Q

Pharmacological treatment pre-op in phaeochromocytomas

A

Alpha adrenoreceptor antagonist first

Beta receptor antagonists often needed after alpha blockers due to side effect of tachycardia or if tumour predominately secretes adrenaline or dopamine

46
Q

Theoretical risk if beta blockers started before alpha blockers in phaeochromocytoma

A

Increasing peripheral vasoconstriction causing hypertensive crisis

Beta blockade removes protective action of beta 2 peripheral vasodilatation

47
Q

Intraoperative agents of choice

A

Esmolol

Propranolol

Labetalol

Phenoxybenzamine

Doxazosin

48
Q

Features of Esmolol

A

Relatively cardio selective

Fast onset and offset

49
Q

Esmolol dose and route of administration

A

25 - 100 mg boluses IV

Can be given as infusion 50 - 150 microgram/kg/min

50
Q

Propranolol dose intraoperatively

A

1 mg over 1 minute

Repeated as necessary

51
Q

Labetalol mechanism of action

A

Selectively antagonises alpha 1 and beta adrenoreceptors

1:3 alpha : beta when given PO
1:7 alpha : beta when given IV

Reduces BP by decreasing HR, CO and SVR

52
Q

Metabolism of Labetalol

A

Metabolised in liver

Significant first pass effect

50% plasma protein bound

53
Q

Benefits of Labetalol use

A

No significant effect on airways or cerebral perfusion

54
Q

Indications for Labetalol use

A

Pregnancy induced hypertension

Phaeochromocytoma

Deliberate perioperative hypotension

55
Q

Side effects of Labetalol

A

Same as other beta blocker side effects

Also can cause jaundice

56
Q

Advantages of phenoxybenzamine use in phaeochromocytomas

A

Long duration of action

57
Q

Disadvantages of phenoxybenzamine use in pheaochromocytomas

A

Also blocks alpha 2 which regulates noradrenaline release and can result in tachycardias requiring beta blockade

Treatment stopped 24-48 hours prior to surgery but residual blockade can remain which is unresponsive to alpha agonists

58
Q

Advantages of doxazosin use in phaeochromocytomas

A

Selective alpha 1 antagonist - no associated tachycardias, less beta blocker requirement

Long duration of action

Does not cross blood brain barrier

59
Q

Disadvantages of doxazosin use in phaeochromocytomas

A

Postural hypotension can be severe at onset on treatment

Massive catecholamine surges during surgery can displace drug from receptor

Anaesthetic FRCA Primary - eLFH Pharmacology (10 decks)

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