Diltiazem and Theophylline Interaction
Drug interaction information between Diltiazem and Theophylline.
Diltiazem and Theophylline have a documented major interaction in FDA labeling.
FDA drug labeling documents a major-severity interaction between Diltiazem and Theophylline. Major interactions are generally avoided, moderate ones may need monitoring or a dose adjustment, and minor ones are usually low-risk. This page shows the documented mechanism and guidance. Label-documented interactions are not a complete safety review, so always confirm your own medications with a pharmacist or doctor. Educational information, not medical advice.
How They Interact
Diltiazem can slow down the liver's ability to break down theophylline. This can cause the medicine to build up in your body and reach toxic levels.
What To Do
Your doctor may need to lower your theophylline dose while you are taking diltiazem. Watch for signs of too much medicine, such as nausea, tremors, or a fast heartbeat.
FDA Label Information
albuterol, systemic and inhaled mebendazole amoxicillin medroxyprogesterone ampicillin, with or without sulbactam methylprednisolone atenolol metronidazole azithromycin metoprolol caffeine, dietary ingestion nadolol cefaclor nifedipine co-trimoxazole (trimethoprim and sulfamethoxazole) nizatidine diltiazem norfloxacin dirithromycin ofloxacin enflurane omeprazole famotidine prednisone, prednisolone felodipine ranitidine finasteride rifabutin hydrocortisone roxithromycin isoflurane Sorbitol (purgative doses do not inhibit theophylline absorption) isoniazid sucralfate isradipine terbutaline,...
Diltiazem Also Interacts With
- Ezetimibe major
- Ezetimibe/Simvastatin major
- Simvastatin major
- Rifampin moderate
- Digoxin moderate
Theophylline Also Interacts With
- Metoprolol major
- Albuterol major
- Omeprazole major
- Amoxicillin major
- Famotidine major
Frequently Asked Questions
Can I take Diltiazem and Theophylline together?
This is a major interaction. Your doctor may need to lower your theophylline dose while you are taking diltiazem. Watch for signs of too much medicine, such as nausea, tremors, or a fast heartbeat.
How serious is the interaction between Diltiazem and Theophylline?
This interaction is classified as "major" severity by the FDA. Major interactions may be life-threatening or cause serious side effects.
Why do Diltiazem and Theophylline interact?
Diltiazem can slow down the liver's ability to break down theophylline. This can cause the medicine to build up in your body and reach toxic levels.
Understanding the Diltiazem and Theophylline Interaction
FDA-approved prescribing information for these two drugs flags their combination as a major-severity interaction. Diltiazem belongs to the Calcium Channel Blocker class and Theophylline belongs to the Methylxanthine Bronchodilator class - two categories that can collide when co-prescribed. The mechanism described in FDA labeling is: Diltiazem can slow down the liver's ability to break down theophylline. Severity tiers matter: major flags generally advise avoidance, moderate flags often require monitoring or dose adjustment, and minor flags may only call for awareness.
Context around a specific patient determines real-world impact. Diltiazem has 46 total documented interactions on file in this dataset, and Theophylline has 86. Each additional medication compounds the interaction surface, which is why pharmacists run full-profile checks rather than evaluating one pair at a time. FDA-derived guidance for this pair is: Your doctor may need to lower your theophylline dose while you are taking diltiazem. Timing of doses, renal and hepatic function, age, and other concurrent prescriptions all shape whether a labeled interaction matters clinically.
An interaction flag is not a verdict. A large share of labeled interactions are managed routinely in clinical practice, the fix may be as simple as spacing doses or adding a monitoring test. Others require the prescriber to choose a different medication entirely. This page surfaces FDA-sourced labeling and openFDA data for educational purposes only; it is not medical advice and cannot account for your full clinical picture. Never start, stop, or adjust either Diltiazem or Theophylline based on a web page, speak with your prescriber or pharmacist before making any change.
Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. Always consult your healthcare provider about drug interactions.
Read our methodology - how this data is sourced, computed, and verified.