Dear Thinh, Hi I can understand your concern regarding the safety of Allopurinol. Apart form precipitating acute gouty arthritis during initial therapy, the most common side effects of Allopurinol include skin rashes, drowsiness or dizziness, vomiting, loose motions and abdominal pain. Other less common side effects peripheral neuritis, vasculities, include bone marrow toxicity, liver damage, bone marrow suppression, and aplastic anemia. Liver toxicity and interstitial nephritis have been reported. Since you have decreased renal function, the half life in the plasma gets prolonged hence you require lower doses of Allopurinol than those with normal renal function. And you also need be observed closely for the possible side effects during administration of Allopurinol. Therefore, a dose of 200 mg per day or 300 mg twice a week, or perhaps less, may be sufficient to maintain the reduced serum uric acid levels. Hope this answers your query.