Treatment of bronchial asthma by sympathomimetic drugs.
Sympathomimetic Drugs or adrenergic agents are drug of choice for bronchodilation. The most probable mechanism of action of adrenergic drugs is that they stimulate beta receptors. This stimulation result in increased cAMP production in bronchial muscle cell and hence relaxes the bronchial muscles.
Increased cAMP production in the mast cell also decreases the mediator release due to antigen antibody reactions. The adrenergic drugs should be used with up most care in the hypertensive patients and patients receiving digitalis. The most preferred route for administration of sympathomimetics is through inhalation.
Individual sympathomimetics for the treatment of asthma.
Adrenaline- Adrenaline is sympathomimetic drug with alpha, beta1 and beta2 agonist activity. The antiasthmatic action of adrenaline is due to its strong affinity to beta2 receptor. As this drug is not selective in its action because it also associated with rise of blood pressure and cardiac stimulation so adrenaline is no more drug of choice for asthma.
Ephedrine- Ephedrine is also sympathomimetic drug with alpha, beta1 and beta2 agonist activity. It causes slow bronchodilation which lasts from 3 to 5 hours. Ephedrine is now seldom used in the treatment of asthma due to its low efficacy and side effects. Earlier ephedrine was used in combination for the treatment of mild and moderate asthma.
Isoprenaline- Isoprenaline is beta1 and beta2 agonist. The bronchodilation caused by the isoprenaline last for 1 to 2 hours. This drug was removed from the market due to its induced tachycardia due to beta1 stimulation.
4. Orciprenaline- The action of orciprenaline is similar to isoprenaline but it is slightly more selective beta2 agonist than isoprenaline. Orciprenaline is an orally effective antiasthmatic and have a bronchodilating effect ranging from 3 to 4 hours. The emergence of new more selective beta2 agonist has resulted in the withdrawal of this drug from the market.
5. Salbutamol (Albuterol) – Salbutamol is highly selective beta2 agonist. This drug is safer and long lasting than isoprenaline but have similar efficacy. The major side effects of salbutamol are cardiac arrests, palpitation, restlessness, nervousness, throat irritation and ankle edema.
6. Terbutaline- Terbutaline has almost similar mechanism action and pharmacological properties as of salbutamol. At present, salbutamol and terbutaline are the most popular drugs for asthma. They are administered through inhalation. It is seen in most of the cases that both of the drugs doesn’t produce any response after some time.