Beta Blockers Flashcards
(21 cards)
Beta blocker indications
Hypertension Angina HF Arrhythmia (AF, A. flutter, SVT) Thyrotoxicosis Migraine prophylaxis Anxiety
Where are B1 receptors found?
Heart
Kidneys
Where are B2 receptors found?
Blood vessels
Bronchi
Kidneys
B-blocker mechanism of action
Antagonise post-synaptic B-adrenoreceptors with varying selectivity
Connected to cAMP pathway which initiates NE release
Commonly used B-blockers and their selectivity
Metoprolol – B1
Atenolol – B1
Propanolol – B1/2
Labetalol – B1/2 + alpha (used in pregnancy)
Water soluble B-blockers
E.g., atenolol
Excreted via kidneys, long half life
Lipid soluble B-blockers
E.g., propanolol, metoprolol
Metabolised by liver, short half life. Can be encapsulated to prolong metabolism.
B-blocker pharmacokinetics
Well-absorbed orally Sustained release preparations available Some IV preparations Variable lipophilicity More lipophilic = better at crossing BBB
Effects of B-blockers on CNS
Lower BP - Reduce CO - Reset baroreceptors - Renin inhibition - Direct sympathetic activity reduction Negatively chronotropic
Inotropic effects of B-blockers
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
Respiratory effects of B-blockers
B2 receptor antagonism therefore contraindicated in asthmatics
Eye effects of B-blockers
Reduce aqueous humour production, give topically
Metabolic effects of B-blockers
Decrease gluconeogensis via B2 receptors
Slow down hypoglycaemia resolution and mask some symptoms of hypoglycaemia therefore care must be taken in diabetics
Thyroid effects of B-blockers
T4- —> T3 conversion under control of B receptors therefore can inhibit T3 production and relieve thyrotoxicosis symptoms
Use propanolol
Adverse effects of B-blockers
Asthma exacerbation Hypotension Bradycardia Vasospasm Fatigue Impotence Nightmares Withdrawal
How do B-blockers cause withdrawal?
Long-term use can upregulate post-synaptic receptors therefore slow retraction of drug necessary
B-blocker interactions
Contraindicated with verapamil (marked negative chronotropic effect)
Diltiazem (caution but acceptable)
Other BP lowering drugs
Antidiabetics (hypoglycaemia awareness)
B-blockers in angina
Reduce heart rate and cardiac work
Metoprolol and atenolol
B-blockers post-MI
Decrease arrhythmia
Decrease ventricular rupture
Increase cardiac remodelling
B-blockers in heart failure
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)
B-blockers and hypertension
Not 1st choice, but if patient also has AF and/or HF, should be considered
Metoprolol
