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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
Phenoxybenzamine mechanism of action
Irreversible blockade of alpha adrenoreceptors Inhibits catecholamine uptake into neurones
26
Phenoxybenzamine duration of action
Half life 24 hours Lasts until new receptors are produced
27
Side effects of phenoxybenzamine
Reflex tachycardia due to alpha 2 antagonism Miosis Sedation
28
Classification of Beta adrenoreceptor antagonists
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
Non selective beta receptor antagonist examples
Carvedilol Labetalol Propranolol Timolol Sotalol
30
Selective beta 1 antagonist examples
Atenolol Metoprolol Esmolol Bisoprolol Nebivolol
31
Effects of beta adrenoreceptor antagonists
Negative inotropy and chronotropy Reduces sinoatrial node automaticity Decreases atrioventricular node conduction Increases time in diastole increasing O2 supply to myocardium
32
Indications for beta adrenoreceptor antagonist use
IHD - angina and post MI Arrhythmias Congestive heart failure Phaeochromocytoma (in conjunction with alpha blockers) Thyrotoxicosis (propranolol) Migraine prophylaxis Glaucoma
33
Side effects of beta adrenoreceptor antagonists
Cool extremities with reduced peripheral circulation Bronchospasm in susceptible people Masks hypoglycaemia symptoms Some cross blood brain barrier Urinary retention Increased uterine tone
34
Effects of beta adrenoreceptor antagonists when they cross blood brain barrier
Hallucinations Nightmares Depression
35
Intrinsic sympathomimetic activity definition
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
Examples of beta receptor antagonists with intrinsic sympathomimetic activity
Timolol Acebutolol Pindolol
37
Intended benefits of beta blockers with intrinsic sympathomimetic activity
Theoretically less likely to cause bradycardia but not been shown to be beneficial post MI
38
Use of beta receptor antagonists in cardiac failure
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
Examples of beta adrenoreceptor antagonists that are beneficial in heart failure
Carvedilol (most successful) Bisoprolol Metoprolol
40
Possible mechanisms of action of beta blockers in providing benefit to cardiac failure patients
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
Phaeochromocytoma definition
Tumour of chromaffin cells in adrenal medulla (or in other paraganglia of sympathetic nervous system) Increased circulating catecholamines (norad, adrenaline, dopamine) Rare
42
Symptoms of phaeochromocytoma
Noradrenaline - HTN refractory to treatment Adrenaline and Dopamine - episodic panic attacks and palpitations
43
Management of phaeochromocytoma
Surgical Pharmacological treatment pre-op
44
Goals of pharmacological treatment pre-op for phaeochromocytoma
Good BP control Treatment of significant arrhythmias Restoration of circulating blood volume
45
Pharmacological treatment pre-op in phaeochromocytomas
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
Theoretical risk if beta blockers started before alpha blockers in phaeochromocytoma
Increasing peripheral vasoconstriction causing hypertensive crisis Beta blockade removes protective action of beta 2 peripheral vasodilatation
47
Intraoperative agents of choice
Esmolol Propranolol Labetalol Phenoxybenzamine Doxazosin
48
Features of Esmolol
Relatively cardio selective Fast onset and offset
49
Esmolol dose and route of administration
25 - 100 mg boluses IV Can be given as infusion 50 - 150 microgram/kg/min
50
Propranolol dose intraoperatively
1 mg over 1 minute Repeated as necessary
51
Labetalol mechanism of action
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
Metabolism of Labetalol
Metabolised in liver Significant first pass effect 50% plasma protein bound
53
Benefits of Labetalol use
No significant effect on airways or cerebral perfusion
54
Indications for Labetalol use
Pregnancy induced hypertension Phaeochromocytoma Deliberate perioperative hypotension
55
Side effects of Labetalol
Same as other beta blocker side effects Also can cause jaundice
56
Advantages of phenoxybenzamine use in phaeochromocytomas
Long duration of action
57
Disadvantages of phenoxybenzamine use in pheaochromocytomas
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
Advantages of doxazosin use in phaeochromocytomas
Selective alpha 1 antagonist - no associated tachycardias, less beta blocker requirement Long duration of action Does not cross blood brain barrier
59
Disadvantages of doxazosin use in phaeochromocytomas
Postural hypotension can be severe at onset on treatment Massive catecholamine surges during surgery can displace drug from receptor

Anaesthetic FRCA Primary - eLFH Pharmacology (11 decks)

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