Allopurinol and Amoxicillin Interaction
Drug interaction information between Allopurinol and Amoxicillin.
Allopurinol and Amoxicillin have a documented moderate interaction in FDA labeling.
FDA drug labeling documents a moderate-severity interaction between Allopurinol and Amoxicillin. 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
Taking these two medicines at the same time increases the chance that you will develop a skin rash. It is not fully known if the drugs themselves or the high uric acid levels in the body cause this reaction.
What To Do
Watch for any signs of a skin rash and contact your healthcare provider immediately if one appears.
FDA Label Information
( 7.1 ) Concomitant use of Amoxicillin and Clavulanate Potassium and oral anticoagulants may increase the prolongation of prothrombin time.( 7.2 ) Co-administration with allopurinol increases the risk of rash. 7.3 Allopurinol The concurrent administration of allopurinol and amoxicillin increases the incidence of rashes in patients receiving both drugs as compared to patients receiving amoxicillin alone. It is not known whether this potentiation of amoxicillin rashes is due to allopurinol or the hyperuricemia present in these patients.
Allopurinol Also Interacts With
- Pegloticase major
- Cyclosporine moderate
- Amoxicillin/Clavulanate moderate
- Warfarin minor
- Theophylline minor
Amoxicillin Also Interacts With
- Lansoprazole major
- Rabeprazole major
- Theophylline major
- Probenecid moderate
- Estradiol minor
Frequently Asked Questions
Can I take Allopurinol and Amoxicillin together?
This is a moderate interaction. Watch for any signs of a skin rash and contact your healthcare provider immediately if one appears.
How serious is the interaction between Allopurinol and Amoxicillin?
This interaction is classified as "moderate" severity by the FDA. Moderate interactions may worsen your condition or change how your medications work.
Why do Allopurinol and Amoxicillin interact?
Taking these two medicines at the same time increases the chance that you will develop a skin rash. It is not fully known if the drugs themselves or the high uric acid levels in the body cause this reaction.
Understanding the Allopurinol and Amoxicillin Interaction
FDA-approved prescribing information for these two drugs flags their combination as a moderate-severity interaction. Allopurinol belongs to the Xanthine Oxidase Inhibitor class and Amoxicillin belongs to the Penicillin Antibiotic class - two categories that can collide when co-prescribed. The mechanism described in FDA labeling is: Taking these two medicines at the same time increases the chance that you will develop a skin rash. 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. Allopurinol has 10 total documented interactions on file in this dataset, and Amoxicillin has 12. 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: Watch for any signs of a skin rash and contact your healthcare provider immediately if one appears. 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 Allopurinol or Amoxicillin 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.