ß2 Agonists

ß2-adrenoceptor agonists are probably the most common prescribed medication in respiratory practice. They are used in the treatment of asthma and the reversible element of airways obstruction commonly found in patients with COPD. Although there are several different types of ß2-agonist, most are pharmacologically similar and all are used in a similar fashion. All ß2-agonists are commonly administered by inhalation of the drug as an aerosol (either from a metered dose inhaler (MDI) or a nebuliser) or as powder delivery systems.

Theophylline works as a bronchodilator by the relaxation of bronchial smooth muscle. Theophylline has also been shown to increase the force of contraction of the diaphragm in patients with COPD. Theophylline produces bronchodilatation in a concentration dependent manner and continuous therapy can reduce the symptoms of chronic asthma. However, theophylline also reduces dyspnoea in patients with COPD without alteration of their lung function that could be due to a central, cardiovascular of diaphragmatic effect.

One of the factors that limits the usefulness of theophylline is the high incidence of side effects within the therapeutic range and the narrow therapeutic index. As plasma levels exceed normal therapeutic range the frequency of side effects increases, the most common being a sinus tachycardia, nausea, tremor and indigestion. Indigestion is probably due theophylline increasing gastric secretion and relaxing the gastro-oesophageal sphincter causing gastro-oesophageal reflux.