Acyclovir and Tizanidine Interaction
Drug interaction information between Acyclovir and Tizanidine.
Acyclovir and Tizanidine have a documented minor interaction in FDA labeling.
FDA drug labeling documents a minor-severity interaction between Acyclovir and Tizanidine. 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
Acyclovir blocks a specific liver enzyme that breaks down tizanidine. This causes the muscle relaxant to stay in your body at much higher levels, which can be dangerous.
What To Do
You should avoid taking these two medications together to prevent serious side effects.
FDA Label Information
7.2 Moderate or Weak CYP1A2 Inhibitors Concomitant use of tizanidine with moderate or weak CYP1A2 inhibitors (e.g., zileuton, antiarrhythmics [amiodarone, mexiletine, propafenone, and verapamil], cimetidine, famotidine, oral contraceptives, acyclovir, and ticlopidine) should be avoided.
Acyclovir Also Interacts With
- Bictegravir/Emtricitabine/Tenofovir minor
- Cidofovir minor
- Emtricitabine/Tenofovir minor
- Meperidine minor
- Tenofovir Disoproxil minor
Tizanidine Also Interacts With
- Ciprofloxacin major
- Fluvoxamine major
- Famotidine moderate
- Verapamil minor
- Amiodarone minor
Frequently Asked Questions
Can I take Acyclovir and Tizanidine together?
This is a minor interaction. You should avoid taking these two medications together to prevent serious side effects.
How serious is the interaction between Acyclovir and Tizanidine?
This interaction is classified as "minor" severity by the FDA. Minor interactions are unlikely to cause significant problems but should still be mentioned to your healthcare provider.
Why do Acyclovir and Tizanidine interact?
Acyclovir blocks a specific liver enzyme that breaks down tizanidine. This causes the muscle relaxant to stay in your body at much higher levels, which can be dangerous.
Understanding the Acyclovir and Tizanidine Interaction
FDA-approved prescribing information for these two drugs flags their combination as a minor-severity interaction. Acyclovir belongs to the Antiviral (Nucleoside Analog) class and Tizanidine belongs to the Central Alpha-2 Agonist (Muscle Relaxant) class - two categories that can collide when co-prescribed. The mechanism described in FDA labeling is: Acyclovir blocks a specific liver enzyme that breaks down tizanidine. 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. Acyclovir has 7 total documented interactions on file in this dataset, and Tizanidine has 17. 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: You should avoid taking these two medications together to prevent serious side effects. 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 Acyclovir or Tizanidine 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.