Salbutamol (Albuterol)

• Salbutamol (also known as Albuterol) is a short-acting β₂-adrenergic receptor agonist (SABA) used primarily as a bronchodilator to relieve symptoms of asthma, chronic obstructive pulmonary disease (COPD).
• It works by relaxing the smooth muscles in the airways, leading to bronchial dilation and easier breathing.

Chemical Structure & Formula

• Chemical Formula: C₁₃H₂₁NO₃
• Structure:
• 

Mechanism of Action (Detailed)

• Salbutamol is a selective β2-adrenergic agonist → Bronchodilation & Smooth muscle relaxation.

• β2 Activation:

  • Relaxes bronchial smooth muscle → Bronchodilation.
  • Inhibits inflammatory mediators in mast cells → Reduces airway inflammation.
  • Increases mucociliary clearance → Removes mucus from airways.

Structure-Activity Relationship (SAR)

1. Aromatic Ring Substitution:

   • Two OH groups at 3,5-position (resorcinol-type): gives β2-selectivity and prevents COMT metabolism.

2. β-OH on Ethanolamine Chain:

   • Required for direct interaction with β2 receptors.

3. N-substitution:

   • Bulky t-butyl group on nitrogen: provides β2-selectivity over β1.

4. Stereochemistry:

   • (R)-enantiomer has more activity; commercial salbutamol is usually a racemic mixture.

5. Resistance to COMT:

   • Lack of catechol (1,2-dihydroxy) structure makes it more orally bioavailable.

Synthesis of Salbutamol

Side Effects of Salbutamol

• Tachycardia & Palpitations (mild β1 activation at high doses).
• Tremors (β2 stimulation in skeletal muscle).
• Hypokalemia (β2-mediated intracellular K+ uptake).
• Hyperglycemia (mild increase in glycogenolysis).

Clinical Uses of Salbutamol

• Bronchial asthma (first-line rescue inhaler).
• COPD (acute symptom relief).
• Exercise-induced bronchospasm prevention.

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