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SNS inhibitors
Drugs that inhibit the sympathetic nervous system are often used in the treatment of cardiovascular disease
- uses
- classes
- mechanism
- dose and half-life
- adverse drug reactions
- counter-indications and drug interactions
- metabolism and excretion
- dependency
Uses
- moderate to severe hypertension
- angina
- congestive heart failure
- acute coronary syndromes, though no real evidence of improving outcomes
Classes
Centrally acting
- act on the BP control centre in the brain
- thought that they act on α2 receptors to inhibit NE release
- side effects include sedation
- methyldopa
- clonidine
Beta-blockers
- decrease cardiac output (both HR and contractility)
- also decrease renin release, leading to lowered Na, water retention and vasodilation
- can be used (off-label) for stage fright
- makes exercise difficult
- propanolol: β1 and β2 antagonist
- metoprolol: β1 antagonist
- atenolol
- acebutamol
- bisoprolol
Alpha-blockers
- block α1 receptors on vascular smooth muscle cells, increasing vasodilation
- parazosin
Mechanism
- competitively inhibits beta1 receptors reducing HR, contractility, BP, and MVO2
- increases duration of diastole
Dose and Half Life
oral therapy sufficient in most case of ACS, though IV metoprolol can also be done 5mgx3 over 15 min
Adverse Drug Reactions
increasing doses of beta blockers causes loss of cardioselectivity and
short term
- avoid acute adminstration in unstable patients with hypotension or overt HF
- bradycardia and heart block
- bronchospasm
- peripheral vasoconstricion
- fatigue, lethargy
long term
- depression, vivid dreams, nightmares
Counter-Indications and Drug Interactions
- absolute: asthma
relative:
- tendency to bronchospasm
- insulin dependent T2DM
- conduction system disease
- peripheral vascular disease
Metabolism and Excretion