Drug interactions
Isoniazid + Theophylline
Severity: Moderate
Isoniazid and Theophylline: moderate interaction.
Last updated Sources: US FDA label
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Isoniazid may raise theophylline concentrations in some patients, with a risk of toxicity. The effect is variable and appears to depend on acetylator status.
What this interaction means in plain words
Isoniazid and Theophylline can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Isoniazid belongs to Anti Bacterial; Theophylline belongs to Respiratory.
Why it happens
Isoniazid inhibits hepatic CYP1A2 and other P450 enzymes that metabolize theophylline.
What to do
Monitor theophylline levels and signs of toxicity when isoniazid is started, and reduce the theophylline dose if needed.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Isoniazid and Theophylline, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 7 days on the web. No card needed.
References
- Theophylline (Anhydrous) - FDA drug label (DailyMed) — openFDA / DailyMed
Other interactions of Theophylline
- Riociguat + Theophylline Contraindicated
- Adenosine + Theophylline Major
- Apalutamide + Theophylline Major
- Bupropion + Theophylline Major
- Carvedilol + Theophylline Major
- Cimetidine + Theophylline Major
Other interactions of Isoniazid
Frequently asked questions
Can I take Isoniazid with Theophylline?
MediHelp rates the interaction as moderate. Isoniazid and Theophylline can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Isoniazid may raise theophylline concentrations in some patients, with a risk of toxicity. The effect is variable and appears to depend on acetylator status.
How serious is the interaction between Isoniazid and Theophylline?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor theophylline levels and signs of toxicity when isoniazid is started, and reduce the theophylline dose if needed.
What other medicines interact with Theophylline?
MediHelp also lists interactions of Theophylline with, for example, Riociguat, Adenosine, Apalutamide. The full list is on the Theophylline page.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
