Beta Adrenergic Blockers

• Beta Adrenergic Blockers inhibit the stimulation of beta-adrenergic receptors (β1 and β2), leading to decreased heart rate, cardiac output, and oxygen demand.
• Beta Adrenergic Blockers are commonly used for hypertension, angina, heart failure, arrhythmias, and anxiety disorders.

Structure-Activity Relationship (SAR) of Beta Blockers

• The SAR of beta blockers is important for understanding their pharmacological properties:
  1. Aromatic Ring: Essential for receptor binding.
  2. Ethanolamine Side Chain: Required for beta receptor interaction.
  3. Hydrophobic Groups: Affect lipid solubility and penetration into the CNS.
  4. Para-substitutions: Increase beta-1 selectivity.
  5. Presence of Additional Functional Groups: Determines cardioselectivity and intrinsic sympathomimetic activity (ISA).

Classification:

1. Non-Selective Beta Blockers (β1 and β2 blockers)

   • These block both β1 (cardiac) and β2 (bronchial and vascular) receptors, leading to decreased heart rate but also potential bronchoconstriction.
   • Example drugs: Propranolol, Metipranolol

2. Selective Beta-1 Blockers (Cardioselective beta blockers)

   • These preferentially block β1 receptors in the heart, reducing heart rate and cardiac workload with minimal effects on β2 receptors (lungs).
   • Example drugs: Atenolol, Betaxolol, Bisoprolol, Esmolol, Metoprolol

3. Mixed Alpha and Beta Blockers

   • These block both alpha and beta receptors, leading to a combined effect of vasodilation and reduced cardiac output.
   • Example drugs: Labetalol, Carvedilol

Effects of Beta Blockers

• Decrease heart rate (negative chronotropic effect)
• Reduce myocardial contractility (negative inotropic effect)
• Lower blood pressure
• Decrease renin release from the kidneys
• Reduce oxygen demand of the heart (useful in angina)
• Bronchoconstriction (in non-selective beta blockers)

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