Zafirlukast Theophylline

Administration of zafirlukast and aspirin increases plasma levels of zafirlukast, When zafirlukast is administered with warfarin, there is an increased effect of the anti coagulant. Administration of zafirlukast and theophylline or erythromycin may result in a decreased level of zafirlukast. Administration of montelukast with other drugs has not revealed any adverse responses. Administration of montelukast with aspirin and NSAIDs is avoided in patients with known aspirin sensitivity. Administration of zileuton with propranolol increases the activity or the propranolol with theophylline increases serum theophylline levels and with warfarin may increase prothrombin time (PT). A prothrombin blood test should be done regularly in the event dosages of warfarin need to be decreased. 

Drugs that may affect zafirlukast include aspirin, erythromycin, and theophylline. Drugs that may be affected by zafirlukast include warfarin. 

Zafirlukast and montelukast are well tolerated. Zafirlukast increases plasma concentrations of warfarin and decreases the concentrations of theophylline and erythromycin. In rare cases, treatment of patients with CysLT receptor antagonists is associated with the development of Churg-Strauss syndrome, a condition marked by acute vasculitis, eosinophilia, and a worsening of pulmonary symptoms. Because these symptoms often appear when patients are given the leukotriene receptor antagonists when they are being weaned from oral corticosteroid therapy, it is not clear whether they are related to the action of the antagonists or are due to a sudden reduction in corticosteroid therapy. 

Katial RK, Stelzle RC, Bonner MW, Marino M, Cantilena LR, Smith LJ. A drug interaction between zafirlukast and theophylline. Arch Intern Med 1998 158(15) 1713-1715. 

Theophylline [the OFF i lin] is a bronchodilator that relieves airflow obstruction in chronic asthma, and decreases the symptoms of the chronic disease. Previously the main-stay of asthma therapy, theophylline has been largely replaced with (3-agonists and corticosteroids. Theophylline is well absorbed by the gastrointestinal tract, and several sustained-release preparations are available. The drug has a narrow therapeutic window, and an overdose of the drug may cause seizures or potentially fatal arrhythmias. Further, theophylline interacts adversely with many drugs. See pp. 450-451 for a description of newly approved drugs, zileuton, zafirlukast, and montelukast. 

THEOPHYLLINE LEUKOTRIENE RECEPTOR ANTAGONISTS -ZAFIRLUKAST Possibly t theophylline levels. Also possibly 4 zafirlukast levels Mutual alteration of metabolism Be aware watch for features of theophylline toxicity and measure levels... 

The plasma concentrations of zafirlukast are reduced when it is administered concurrently with theophylline (7). Conversely, zafirlukast can increase serum theophylline concentrations. 

A 15-year-old girl with asthma, who had taken theophylline 300 mg bd for several years, with serum concentrations of about 61 pmol/l started to take zafirlukast (9). Her serum theophylline concentration increased to 133 pmol/l. Rechallenge confirmed the effect. 

---