PHARMACOTHERAPY OF BRONCHIAL ASTHMA

Drug used in the treatment of bronchia asthma can be grouped into three main categories:

1. Bronchodilators
   1. b- Adrenergic agonists which include:
      • Non selective b-agonists e.g. adrenaline
      • Selective b-agonists e.g. salbutamol
   2. Methylxanthines; theophylline derivatives
   3. Muscranic receptor antagonists e.g. Ipratropium bromide
2. Mast cell stabilizers, e.g. cromolyn sodium, nedocromil, ketotifen
3. Antiinflammatory agents: corticosteroids

1.  b- ADRENERGIC AGONISTS (SYMPATHOMIMETIC AGENTS)

1. Non- selective- b-agonists
   1. Epinephrine, ephedrine, isoprotenerol
2. Selective b-agonists
   1. Salbutamol, terbutaline, metaproterenol, salmeterol, formaterol and etc

Mechanism of Action

b-Agonists stimulate adenyl cyclase and increase formation of cAMP in the airway tissues. They have got several pharmacological actions important in the treatment of asthma

• Relax smooth muscles
• Inhibit release of inflammatory mediator or broncho constricting substances from mast cells.
• Inhibit microvasculature leakage
• Increase mucociliary transport

Non-selective b- agonists

1. Cause more cardiac stimulation (mediated by a b1 receptor), they should be reserved for special situation.
2. Epinephrine: very effective, rapidly acting bronchodilator especially preferable for the relief of acute attack of bronchial asthma.
3. Administered by inhalation or subcutaneously.

Side effects include arrhythmia and worsening of angina pectoris, increase blood pressure, tremors etc

Contraindication: – hypertension, arrhythmia,

Ephedrine: compared to epinephrine, it has longer duration of action but more pronounced central effect and lower potency. It can be given orally. The drug is currently infrequently used because of development of more efficacious and beta₂-selective agents.

Selective b₂– selective agonists

Largely replaced non – selective b₂– agonists, are effective after inhaled or oral administration and have got longer duration of action. They are the most widely used sympathomimetics. Commonly used drugs both by oral and inhalation are Salbutamol, terbutaline, metaproterenol, pirbuterol and bitolterol.

Salmeterol and formeterol are new generation, long acting b₂– selective agonists (with duration of action 12 hrs or more). These drugs appear to interact with inhaled corticosteroids to improve asthma control.

Delivery of adrenoreceptor agonists through inhalation results in the greatest local effect on airway smooth muscle with least systemic toxicity.

Side effects

Tremors, anxiety, insomnia, tachycardia, headache, hypertension and etc.

Contraindications: Sympathomimetics are contraindicated in patients with known hypersensitivity to the drugs.

Precautions: They should be used cautiously in patients with hypertension, cardiac dysfunction, hyperthyroidism, glaucoma, diabetes, pregnancy.