In rare cases allopurinol causes severe, possibly lethal hypersensitive reactions that are manifested by different skin reactions (even toxic epidermolysis is possible), fever, eosinophilia, lymphadenopathies, vasculitis, renal and hepatic disorders, and hematological anomalies. Apparently subjects with renal failure are particularly endangered. Occasionally there are isolated occurrences of hematological anomalies and hepatitis.

In general, skin rashes (makulopapular exanthema, urticaria, purpura, etc.) are relatively frequent. Allopurinol should be discontinued immediately in those cases. At the beginning of the treatment, gout seizures can occur more frequently. Other side-effects (nausea, diarrhea) are rare. Whether allopurinol favours the development of cataracts is unclear.

Allopurinol: Interactions

The dissimilation of azathioprine and mercaptopurine is dependent on the xanthine oxidase: reduce dose to 25% when allopurinol is administered concomitantly! Allopurinol can also increase the effect of cyclophosphamide (bone marrow depression) and chlorine propamide (danger of hypoglycemia).

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