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A drug interaction between zafirlukast and theophylline
R K Katial1, R C Stelzle, M W Bonner
1Department of Allergy and Immunology, Walter Reed Army Medical Center, Washington, DC 20307, USA.
Archives of Internal Medicine
|August 13, 1998
Summary
Zafirlukast may increase theophylline levels, potentially causing toxicity in asthma patients. Close monitoring of theophylline levels is recommended when co-prescribing these medications.
Area of Science:
- Pharmacology
- Clinical Medicine
- Drug Interactions
Background:
- Zafirlukast is an asthma medication with a favorable safety profile.
- Theophylline is a common asthma treatment.
- Potential drug interactions require careful evaluation.
Observation:
- A case study involving a 15-year-old asthma patient revealed a significant interaction.
- Concurrent zafirlukast use led to a 7-fold increase in serum theophylline levels.
- Theophylline levels rose to a toxic range, necessitating dose adjustments.
Findings:
- Zafirlukast administration significantly elevated theophylline serum concentrations.
- Theophylline metabolism, primarily via cytochrome P450 (CYP 1A2), may be inhibited by zafirlukast.
- This interaction contrasts with manufacturer data and highlights a potential risk.
Implications:
- Physicians should closely monitor theophylline levels in patients also taking zafirlukast.
- The potential for serious drug-drug interactions exists for asthma patients on combination therapy.
- Further research into the metabolic pathways of zafirlukast and theophylline is warranted.