24. Drugs used in bronchial asthma.

Antiasthmatic drugs

Antiasthmatic drugs are medications used to manage and alleviate symptoms of asthma. They work through various mechanisms to reduce inflammation, prevent bronchoconstriction, and improve airflow in the lungs.

Classification

1. Corticosteroids: Beclometasone
2. Selective beta agonist: Salbutamol
3. Antimuscarinic: Tiotropium
4. Mast cell stabilisers: Cromolyn sodium
5. Leukotriene antagonist: Montelukast
6. Monoclonal antibodies: Omalizumab

(Montelukast is especially useful for exercise-induced and allergic asthma. Cromolyn sodium is less commonly used now due to lower efficacy compared to newer agents.)

Pharmacodynamics

• Corticosteroids exert their pharmacodynamic effects by suppressing inflammation, reducing airway hyperresponsiveness, and inhibiting mucus production by altering gene expression and cytokine release.
• Selective beta agonists stimulate beta2-adrenergic receptors in airway smooth muscle, leading to bronchodilation through increased intracellular cAMP levels.
• Antimuscarinic agents block muscarinic receptors (especially M3), reducing bronchoconstriction and mucus secretion.
• Mast cell stabilisers prevent the release of inflammatory mediators, such as histamine and leukotrienes, from mast cells, thus inhibiting allergic responses.

• Leukotriene antagonists block leukotriene D4 receptors (CysLT1), which reduces bronchoconstriction, eosinophilic inflammation, and mucus secretion.
• Monoclonal antibodies target specific immune pathways involved in asthma, such as IgE (Omalizumab) or interleukins (e.g., IL-5, IL-4, IL-13 in newer agents), to reduce airway inflammation and hyperresponsiveness.