Amoxicillin and Allopurinol Interaction
Drug interaction information between Amoxicillin and Allopurinol.
Amoxicillin and Allopurinol have a documented moderate interaction in FDA labeling.
FDA drug labeling documents a moderate-severity interaction between Amoxicillin and Allopurinol. This page displays the available source-record category and label text. The category is not an individual risk estimate or medication-combination direction.
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.
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.
Amoxicillin Also Interacts With
- Lansoprazole major
- Rabeprazole major
- Theophylline major
- Probenecid moderate
- Estradiol minor
Allopurinol Also Interacts With
- Pegloticase major
- Cyclosporine moderate
- Amoxicillin/Clavulanate moderate
- Warfarin minor
- Theophylline minor
Frequently Asked Questions
What SPL severity band is on file for Amoxicillin + Allopurinol?
Compiled FDA labeling labels this pair moderate. That is a source-record field, not an individual medication-combination decision.
Which drug in this pair has the larger labeled-interaction portfolio?
Amoxicillin has 12 labeled pairs on file vs Allopurinol's 10. In the moderate band specifically: Amoxicillin has 2 (also Probenecid); Allopurinol has 3 (also Cyclosporine, Amoxicillin/Clavulanate).
What mechanism field is on file for Amoxicillin and Allopurinol?
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.
Amoxicillin carries more major-labeled pairs than Allopurinol
SPL source-record counts only. This page's band is moderate · classes on file: Amoxicillin (Penicillin Antibiotic); Allopurinol (Xanthine Oxidase Inhibitor).
Amoxicillin has 3 major-labeled pairs vs Allopurinol's 1. This page itself is in the moderate band, not the major band.
3 major · 2 moderate · 7 minor · 12 total
- Other moderate peers for Amoxicillin
- Probenecid
1 major · 3 moderate · 6 minor · 10 total
- Other moderate peers for Allopurinol
- Cyclosporine
- Amoxicillin/Clavulanate
Sources: FDA Drug Labels (SPL) via openFDA (2026). This is for informational purposes only and is not medical advice. This registry does not provide individual medication-combination directions.
Read our methodology - how this data is sourced, computed, and verified.