A female client with chronic obstructive pulmonary disease (COPD) takes anhydrous theophylline, 200 mg P.O. every 8 hours. During a routine clinic visit, the client asks the nurse how the drug works. What is the mechanism of action of anhydrous theophylline in treating a nonreversible obstructive airway disease such as COPD?
A. It makes the central respiratory center more sensitive to carbon dioxide and stimulates the respiratory drive.
B. It inhibits the enzyme phosphodiesterase, decreasing degradation of cyclic adenosine monophosphate, a bronchodilator.
C. It stimulates adenosine receptors, causing bronchodilation.
D. It alters diaphragm movement, increasing chest expansion and enhancing the lung’s capacity for gas exchange.
Correct Answer: A. It makes the central respiratory center more sensitive to carbon dioxide and stimulates the respiratory drive.
Anhydrous theophylline and other methylxanthine agents make the central respiratory center more sensitive to CO2 and stimulate the respiratory drive. Theophylline is indicated for the treatment of the symptoms and reversible airflow obstruction associated with chronic asthma and other chronic lung diseases, e.g., emphysema and chronic bronchitis.
Option B: Inhibition of phosphodiesterase is the drug’s mechanism of action in treating asthma and other reversible obstructive airway diseases — not COPD. At larger doses, theophylline inhibits phosphodiesterase causing increased cyclic adenosine monophosphate resulting in increased levels of adrenergic activation and catecholamine release.
Option C: Methylxanthine agents inhibit rather than stimulate adenosine receptors. One mechanism is that theophylline blocks adenosine receptors, which has both therapeutic and toxic effects such as bronchodilation, tachycardia, cardiac arrhythmias, seizures, and cerebral vasoconstriction.
Option D: Although these agents reduce diaphragmatic fatigue in clients with chronic bronchitis or emphysema, they don’t alter diaphragm movement to increase chest expansion and enhance gas exchange. Theophylline causes endogenous release of catecholamines through indirect stimulation of beta-1 and beta-2 receptors, which at therapeutic levels cause desired bronchodilation.
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