Beta Blockers

Question 1

Beta blocker indications

Answer 1

Hypertension
Angina
HF
Arrhythmia (AF, A. flutter, SVT)
Thyrotoxicosis
Migraine prophylaxis
Anxiety

Question 2

Where are B1 receptors found?

Answer 2

Heart

Kidneys

Question 3

Where are B2 receptors found?

Answer 3

Blood vessels
Bronchi
Kidneys

Question 4

B-blocker mechanism of action

Answer 4

Antagonise post-synaptic B-adrenoreceptors with varying selectivity
Connected to cAMP pathway which initiates NE release

Question 5

Commonly used B-blockers and their selectivity

Answer 5

Metoprolol – B1
Atenolol – B1
Propanolol – B1/2
Labetalol – B1/2 + alpha (used in pregnancy)

Question 6

Water soluble B-blockers

Answer 6

E.g., atenolol

Excreted via kidneys, long half life

Question 7

Lipid soluble B-blockers

Answer 7

E.g., propanolol, metoprolol

Metabolised by liver, short half life. Can be encapsulated to prolong metabolism.

Question 8

B-blocker pharmacokinetics

Answer 8

Well-absorbed orally
Sustained release preparations available
Some IV preparations
Variable lipophilicity
More lipophilic = better at crossing BBB

Question 9

Effects of B-blockers on CNS

Answer 9

Lower BP
- Reduce CO
- Reset baroreceptors
- Renin inhibition
- Direct sympathetic activity reduction
Negatively chronotropic

Question 10

Inotropic effects of B-blockers

Answer 10

Acute: negative
Long-term: positive
Therefore can be used carefully in HF patients to improve condition, but can worsen fluid overload and decrease contractility if given acutely

Question 11

Respiratory effects of B-blockers

Answer 11

B2 receptor antagonism therefore contraindicated in asthmatics

Question 12

Eye effects of B-blockers

Answer 12

Reduce aqueous humour production, give topically

Question 13

Metabolic effects of B-blockers

Answer 13

Decrease gluconeogensis via B2 receptors

Slow down hypoglycaemia resolution and mask some symptoms of hypoglycaemia therefore care must be taken in diabetics

Question 14

Thyroid effects of B-blockers

Answer 14

T4- —> T3 conversion under control of B receptors therefore can inhibit T3 production and relieve thyrotoxicosis symptoms
Use propanolol

Question 15

Adverse effects of B-blockers

Answer 15

Asthma exacerbation
Hypotension
Bradycardia
Vasospasm
Fatigue
Impotence
Nightmares
Withdrawal

Question 16

How do B-blockers cause withdrawal?

Answer 16

Long-term use can upregulate post-synaptic receptors therefore slow retraction of drug necessary

Question 17

B-blocker interactions

Answer 17

Contraindicated with verapamil (marked negative chronotropic effect)
Diltiazem (caution but acceptable)
Other BP lowering drugs
Antidiabetics (hypoglycaemia awareness)

Question 18

B-blockers in angina

Answer 18

Reduce heart rate and cardiac work

Metoprolol and atenolol

Question 19

B-blockers post-MI

Answer 19

Decrease arrhythmia
Decrease ventricular rupture
Increase cardiac remodelling

Question 20

B-blockers in heart failure

Answer 20

In the damaged heart, the ratio of receptors shifts, increasing the relative proportions of B2 and a1 receptors, therefore carvedilol, a mixed B/a antagonist/antioxidant is a good choice, or metoprolol (B1)

Question 21

B-blockers and hypertension

Answer 21

Not 1st choice, but if patient also has AF and/or HF, should be considered
Metoprolol