Now let us move on to pharmacology. 1st we have is the beta-adrenoceptor agonistBETA-ADRENOCEPTOR AGONISTSPrototypes and Pharmacokinetics:Beta-adrenoceptor agonists are important drugs used to reverse asthmatic bronchoconstriction.Direct-acting α2-selective agonists are the main sympathomimetics used for this purpose.Indirect-acting sympathomimetics like ephedrine, once used, are now obsolete.Short-acting direct-acting agents include albuterol, terbutaline, and metaproterenol, commonly used for their rapid bronchodilator effects in relieving acute symptoms of asthma.Long-acting β2 agonists (LABA) such as salmeterol, formoterol, indacaterol, and vilanterol are also used, but indacaterol and vilanterol are only approved for COPD.Beta agonists are mainly given through inhalation, reducing systemic side effects and delivering the drug directly to the airway smooth muscle.Older drugs have durations of action of 6 hours or less, while salmeterol, formoterol, indacaterol, and vilanterol last 12–24 hours.Mechanism and Effects:Beta-adrenoceptor agonists stimulate adenylyl cyclase, increasing cyclic adenosine monophosphate (cAMP) in smooth muscle cells.This increase in cAMP leads to a powerful bronchodilator response.Clinical Use and Toxicity:Short-acting sympathomimetics (e.g., albuterol, metaproterenol, terbutaline) are first-line therapy for acute asthma, lasting for 4 hours or less.Long-acting agents (e.g., salmeterol, formoterol) are used for prophylaxis due to their 12-hour duration of action.Long-acting agents should not be used for acute episodes due to slow onset of action; they are more effective when combined with corticosteroids.Short-acting β agonists are the most effective bronchodilators and are life-saving for acute asthma.Skeletal muscle tremor is a common adverse effect, and beta2 selectivity is relative, with high doses having significant β1 effects.Cardiac effects like tachycardia can occur even with inhalation, and excessive use can lead to arrhythmias and tremors.Excessive use of short-acting sympathomimetics can lead to loss of responsiveness (tolerance, tachyphylaxis).Patients with COPD, who often have concurrent cardiac disease, may experience arrhythmias even at normal dosages.