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Theophylline
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Theophylline is a long-term control medicine. This means it is used daily to maintain control of your lung disease. It is not one of the first medications used for long-term control of lung diseases. There are safer and more effective medicines available. For people with chronic lung disease theophylline may be added to other medicines to improve symptoms and lung function. Theophylline relaxes the muscles around the airways in the lungs so air can flow more easily into the lungs.
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Theophylline is a potent inhibitor of adenosine receptors at therapeutic concentrations, with antagonism of A1- and A2-receptors, although it is less effective against A3-receptors (40). Although adenosine has little effect on normal human airway smooth muscle in vitro, it constricts airways of patients with asthma via the release of histamine and leukotrienes, suggesting that adenosine releases mediators from sensitized mast cells (41). The receptor involved appears to be an A2b-receptor in humans (although an A3-receptor subserves a similar role in rats) (42). Inhaled adenosine monophosphate causes bronchoconstriction in subjects with asthma, and this is prevented by therapeutic concentrations of theophylline (43). This only confirms that theophylline at therapeutic concentrations is capable of antagonizing the effects of adenosine, and this does not necessarily prove that adenosine receptor antagonism is important for its antiasthma effect. However, adenosine antagonism is likely to account for some of the serious side effects of theophylline, such as seizures and cardiac arrhythmias.
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Theophylline has 2 key mechanisms of action. First, theophylline acts to induce smooth muscle relaxation, resulting in bronchodilation. The exact means by which this occurs remain uncertain. The bronchodilatory effects are believed to be secondary to theophylline's inhibition of 2 isoenzymes of phosphodiesterase (ie, PDE III and PDE IV). Second, theophylline acts to suppress the airway response to irritant stimuli. Other actions induced or promoted by theophylline include diaphragmatic contractility, mucociliary clearance, and lowered pulmonary artery pressure.
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Theophylline has bronchodilator properties and is used in the treatment of asthma and COAD. Theophylline produces bronchodilatation in a concentration dependent manner and continuous therapy can reduce the symptoms of chronic asthma, reduce the dosage of oral corticosteroids in steroid dependent asthma, and reduce the requirement for symptomatic use of ß2-agonists. However, theophylline ... reduces dyspnoea in patients with COAD without alteration of their lung function which could be due to a central, cardiovascular of diaphragmatic effect. Despite theophylline being widely available in a large number of proprietary preparations, little is known about its mode of action. Theophyllines are very popular in the USA and on the continent, but some respiratory physicians in this country still have reservations about its use, mainly because of the high incidence of side effects, particularly at the upper limit of its therapeutic range, and the availability of more potent and less toxic alternatives. However, it still retains an important role in the treatment of acute severe asthma.
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Metabolism Following oral dosing, Theophylline does not undergo any measurable first-pass elimination. In adults and children beyond one year of age, approximately 90% of the dose is metabolized in the liver. Biotransformation takes place through demethylation to 1-methylxanthine and 3-methylxanthine and hydroxylation to 1,3-dimethyluric acid. 1-methylxanthine is further hydroxylated, by xanthine oxidase, to 1-methyluric acid. About 6% of a Theophylline dose is N-methylated to caffeine. Theophylline demethylation to 3-methylxanthine is catalyzed by cytochrome P-450 1A2, while cytochromes P-450 2E1 and P-450 3A3 catalyze the hydroxylation to 1,3-dimethyluric acid.
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Theophylline, another long-term asthma control medication, is available as a tablet, capsule, or syrup. Theophylline relaxes the smooth muscles around the airways. A theophylline blood level between 5-15 mcg/ml usually gives relief of symptoms while avoiding side effects. Theophylline is not one of the first medications used for long-term control of asthma or other chronic lung diseases. There are safer and more effective medicines available, such as inhaled steroids and leukotriene modifiers.
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Theophylline