MODERATE — Monitor Closely
FDA-documented interaction. Rash incidence increases from ~2% to ~20% with combination. Usually not Stevens-Johnson syndrome but can be difficult to distinguish clinically.
Evidence level: STRONG
If you take allopurinol (for gout) and are prescribed amoxicillin, you have a higher than normal chance of developing a skin rash. The rash is usually not dangerous but can be confused with a drug allergy.
Allopurinol significantly increases the risk of skin rash when combined with ampicillin/amoxicillin. Mechanism is not fully understood but may involve immune-mediated hypersensitivity. FDA allopurinol label documents increased rash risk with ampicillin.
If you develop a rash while taking both medications, contact your doctor. The rash may not be a true amoxicillin allergy — but it needs medical evaluation to rule out more serious reactions.
Follow each medication's specific timing instructions. Amoxicillin — check if it requires an empty stomach or should be taken with food. Allopurinol follows its normal schedule. Complete the full antibiotic course as prescribed.
Higher risk for: those with liver or renal impairment, elderly, concurrent use of nephrotoxic or hepatotoxic drugs, history of C. difficile infection, or those on narrow therapeutic index medications (warfarin, digoxin).
Skin rash (usually maculopapular — flat or raised red spots), itching. Seek immediate care if rash is accompanied by blistering, peeling, mouth sores, or fever.
Warn patients about increased rash risk. A rash with this combination does not necessarily indicate true penicillin allergy. Evaluate carefully before labeling patient penicillin-allergic.
Antibiotic interactions are often temporary (duration of treatment). Space supplements and probiotics 2-3 hours away from antibiotic doses. Ask your pharmacist if timing adjustments can reduce the interaction risk.
If you take allopurinol (for gout) and are prescribed amoxicillin, you have a higher than normal chance of developing a skin rash. The rash is usually not dangerous but can be confused with a drug allergy.
Follow each medication's specific timing instructions. Amoxicillin — check if it requires an empty stomach or should be taken with food. Allopurinol follows its normal schedule. Complete the full antibiotic course as prescribed.
Skin rash (usually maculopapular — flat or raised red spots), itching. Seek immediate care if rash is accompanied by blistering, peeling, mouth sores, or fever.
Antibiotic interactions are often temporary (duration of treatment). Space supplements and probiotics 2-3 hours away from antibiotic doses. Ask your pharmacist if timing adjustments can reduce the interaction risk.
Warn patients about increased rash risk. A rash with this combination does not necessarily indicate true penicillin allergy. Evaluate carefully before labeling patient penicillin-allergic.
Or browse the full interaction database (121,000+ pairs).