Asthma beta-adrenoceptor agonists

Beta-adrenoceptor agonists can prodnce or worsen hypoxia acutely in patients with asthma by increasing ventilation-perfusion inequality. It is not known whether this effect is clinically important in patients with asthma not severe enough to require hospital treatment (where supplementary oxygen is standard therapy). 

An alternative hypothesis has been proposed to explain why beta2-agonists lose their bronchoprotective effect while retaining a bronchodilator effect. The beta2-agonists currently available for treating asthma consist of racemic mixtures of equal amounts of two stereoisomers, the i -isomer (or L-isomer), which is the beta-adrenoceptor agonist, and the 5-isomer (o-isomer) which is inactive. 

The most commonly used bronchodUators are the beta-adrenoceptor agonists. In some patients, a muscarinic blocking drug (eg, ipratropium) has a useful bronchodilating effect. Cromolyn and nedocromil inhibit the degranulation of mast cells and are useful as prophylactic agents in some patients. They are not useful in an acute attack. Systemic corticosteroids are reserved for patients with severe asthma who do not respond adequately to other agents, but inhaled steroids (eg, beclomethasone) are standard prophylactic therapy for aU individuals with moderate or severe recurrent asthma... 

Beta Adrenoceptor Agonists - Beta adrenoceptors have been divided into subclasses based on the relative activities of various sympathomimetic amines on different target tissues. For example, beta-1 receptors are found in the heart and beta-2 receptors are found in bronchlolar and other smooth muscle. The potent beta adrenoceptor stimulant Isoproterenol, a common agent for the treatment of asthma, is nonselectlve and may cause undesirable cardiac stimulation at doses which relax bronchlolar smooth muscle. Besides direct effects on bronchial smooth muscle, these compounds inhibit mediator release from skln or passively sensitized human lung and also inhibit antigen-stimulated histamine synthesis in human leucocytes. ... 

The search for potent beta-adrenoceptor agonists (P2-agonists) for the treatment of asthma or chronic bronchitis has a long history and presumably started with the first reports on dyspnea in Chinese textbooks from 2600 The isolation and characterization of adrenaline in... 

Anderson SD, Brannan JD. Long-acting beta 2-adrenoceptor agonists and exercise-induced asthma lessons to guide us in the future. Paediatr Drugs. 2004 6 161-175. 

Q10 Beta-adrenoceptor antagonists are contraindicated in patients with asthma or respiratory obstructive diseases, bradycardia, heart block or heart failure. Adrenergic agonists are contraindicated in patients with closed-angle glaucoma and should be used cautiously in patients with hypertension or heart disease. Parasympathomimetics cause poor night vision and dimming of vision, because of development of miosis, headache and brow ache. Carbonic anhydrase inhibitors have a weak diuretic action and can induce depression, drowsiness, paraesthesia, electrolyte disturbance such as hypokalaemia, acidosis and lack of appetite. 

Taylor DR, Drazen JM, Herbison GP, Yandava CN, Hancox RJ, Town GI. Asthma exacerbations during long term beta agonist use influence of beta[2] adrenoceptor polymorphism. Thorax 2000 55[9] 762 767. 

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