The only consistently observed drug-related side effects is a transient elevation of urine and serum uric acid levels. This rise in uric acid is due to degradation of inosine to uric acid as occurs in the metabolism of the natural purine, inosine, in humans. Infrequent and transient side effects are skin rashes or itching, fatigue or malaise and diarrhea. In rare instance, transient headaches, vertigo, nervousness or insomnia, constipation and polyuria (increased frequency of urination) have been recorded, the frequency of these side effects has no approached statistical significance in over all post-marketing surveillance data.