Drug Interaction Between Theophylline and Letrozole
Direct Answer
There is no documented clinically significant drug interaction between theophylline and letrozole based on available evidence. These medications can be co-administered without specific dose adjustments or enhanced monitoring beyond what is routinely recommended for each drug individually.
Mechanistic Considerations
Letrozole Metabolism and Drug Interactions
- Letrozole is a nonsteroidal aromatase inhibitor that is generally well-tolerated with minimal drug interaction potential 1
- The drug has been studied extensively in combination with other agents (including tamoxifen) without evidence of significant metabolic interference 2
- No CYP450-mediated interactions with theophylline have been reported in clinical trials or post-marketing surveillance 1, 3
Theophylline Interaction Profile
- Theophylline has well-documented interactions with specific drug classes, particularly macrolide antibiotics (erythromycin), fluoroquinolones (ciprofloxacin), calcium channel blockers (verapamil), and H2-blockers (cimetidine) 4, 5
- These interactions typically involve CYP1A2 inhibition, leading to elevated theophylline levels and potential toxicity 4
- Aromatase inhibitors like letrozole are not known to affect CYP1A2 activity, the primary enzyme responsible for theophylline metabolism 1
Clinical Management
Standard Monitoring Approach
- Continue routine theophylline monitoring based on clinical indication (typically targeting serum levels of 5-15 mcg/mL for chronic therapy)
- Monitor for letrozole-specific adverse effects including hot flushes, arthralgia, and potential effects on lipid profile and bone mineral density 1, 3
- No additional theophylline level monitoring is required solely due to letrozole co-administration
Important Caveats
- Be vigilant for true theophylline-interacting drugs that may be prescribed concurrently, as patients on theophylline are exposed to adversely interacting drugs approximately 17.8% of the time they receive theophylline 5
- If theophylline toxicity develops (seizures, arrhythmias, gastrointestinal symptoms), investigate other potential drug interactions or dosing errors rather than attributing it to letrozole 4
Patient Population Considerations
- Both medications are commonly used in postmenopausal women (letrozole for breast cancer, theophylline for respiratory conditions) 6
- No dose adjustment of either medication is required based on co-administration alone