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Beta Blockers

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Colorful pills on ECG

Lets talk beta blockers – because they are so commonly used, it would be silly not to touch on this class of meds.  Whether you are a physician assistant student or a practicing physician assistant, you need to know about beta blockers.

First off, all beta blockers end with the suffix –lol.  Example: Metoprolol, Atenolol, Labetalol, etc.

There are two types of beta blockers:

  1. Non-caridio selective
  2. Caridio selective

They are also divided into three generations.
First generation beta blockers are non-selective and block both Beta-1 and Beta-2 receptors.
Second generation beta blockers are cardio selective and only target Beta-1 receptors.
Third generation beta blockers are non-selective but also cause vasodilation.  The vasodilation occurs through nitric oxide and by blocking the alpha receptors.   

 

First Generation: Propranolol, Nadolol, Timolol.
Second Generation: Metoprolol, Atenolol, Bisoprolol, Esmolol,
Third Generation: Carvedilol and Labetolol

 

Remember, the lungs have Beta-2 receptors (2 lungs) and the heart has Beta-1 receptors (1 heart).  Beta-1 receptors are also found in the kidney (beta blockers allow for decreased renin secretion – preventing the RAAS).  Beta-2 receptors are also found within the vasculature (beta blockers may cause vasoconstriction).

Make note, that at higher drug levels, this cardioselectivity will be lost.

Beta blockers compete with norepinephrine and epinephrine for receptor binding sites. When stimulating Beta-1 receptors, the SA node and AV node are also stimulated.  Therefore, beta blockers prevent norepinephrine/epinephrine from stimulating the AV and SA node. This allows the heart to slow down, decreases contractility, and in turn decreases oxygen demand.  Slowing the conduction through the AV node will also allow for suppression of tachyarrhythmias.

In summary, they decrease heart rate, contractility, and contraction. 

Very important, only three beta blockers have been shown to decrease mortality in CHF: Bisporolol, Carvediolol, and Metoprolol Succinate (longer half life than tartrate).

 

Possible Adverse Reactions:
1. Bradycardia
2. Vasospasm
3. Worsening claudication in PAD
4. Bronchospasm
5. Decreased libido/impotence
6. Depression
7. Mask diabetic hypoglycemic symptoms
8. Hypotension
9. Hypoglycemia or hyperglycemia
10. Hyperkalemia

 

Contraindications:
1. Asthma/COPD – Non Cardio Selective
2. Bradycardia
3. Second/Third degree heart block
4. Cardiogenic Shock
5. Symptomatic peripheral arterial disease
6. Acute CHF exacerbation
7. Pulmonary edema