theophylline + azithromycin

The combination of theophylline and azithromycin represents a potential drug interaction rather than a single formulated product. This is an important clinical consideration when these medications are prescribed together. Theophylline is a bronchodilator used to treat asthma, COPD, and other chronic lung diseases by relaxing the smooth muscle of bronchial airways[1][7]. It works by inhibiting phosphodiesterase enzymes (particularly type III and IV) and blocking adenosine A2B receptors[7]. Azithromycin is a macrolide antibiotic that differs from other macrolides in its interaction profile. Unlike erythromycin and clarithromycin which strongly interact with theophylline, azithromycin appears to have minimal effect on theophylline metabolism in most cases[1][2]. ## Interaction Profile The interaction between theophylline and azithromycin is generally considered minimal compared to other macrolides. While most macrolides are potent inhibitors of cytochrome P450 isoenzyme 3A4 (CYP3A4) and can significantly interfere with theophylline metabolism, azithromycin has little to no effect on theophylline pharmacokinetics in most cases[2]. The explanation for this difference appears to be azithromycin's inability to induce and bind to the cytochrome P450 IIIA enzyme system that metabolizes theophylline[2]. This makes azithromycin a safer choice when an antibiotic is needed for patients already taking theophylline. However, there is at least one case report suggesting a potential interaction upon discontinuation of azithromycin. In this case, a patient experienced an unexpectedly large decrease (80%) in serum theophylline concentration after azithromycin was discontinued[4]. This suggests that withdrawal of azithromycin may, in some circumstances, affect theophylline levels, possibly by leaving an increased number of active enzyme sites available as azithromycin is cleared from the system[4]. ## Clinical Implications When prescribing these medications together, healthcare providers should: 1. Be aware that while the interaction is generally minimal, individual variations may occur 2. Monitor theophylline levels, particularly when starting or stopping azithromycin therapy 3. Watch for changes in theophylline efficacy or toxicity 4. Consider that changes in theophylline levels may occur not only when adding azithromycin but also when discontinuing it This information is particularly relevant for patients with chronic respiratory conditions like COPD or asthma who may require both bronchodilator therapy and antibiotic treatment for respiratory infections.

Brand names

ZithromaxTheo-24Theo24Theo 24Uniphyl

Other names

azithromycin/theophyllineazithromycin and theophylline co-administration