- CAS No.: 315-30-0
- Type: Antigout
ALLOPURINOL Pharmacology: Allopurinol and its active metabolite, oxypurinol, inhibit xanthine oxidase, the enzyme responsible for the conversion of hypoxanthine to xanthine and of xanthine to uric acid. Inhibition of this enzyme accounts for the major pharmacological effects of allopurinol. In addition, allopurinol increases reutilization of hypoxanthine and xanthine for nucleotide and nucleic acid synthesis, via an action involving the enzyme hypoxanthine-guanine phosphoribosyltransferase (HGPRTase). The resultant increase in nucleotide concentration leads to feedback inhibition of de novo purine synthesis. Allopurinol thereby decreases uric acid concentrations in both serum and urine. Accompanying the decrease in uric acid produced by allopurinol is an increase in serum and urine concentrations of hypoxanthine and xanthine. Plasma concentrations of these oxypurines are only slightly increased, and renal clearance is rapid and greater than that of uric acid. In the absence of allopurinol, normal urinary output of oxypurines is almost solely in the form of uric acid. After administration of allopurinol, it is composed of hypoxanthine, xanthine and uric acid. Since each has its independent solubility, the concentration of uric acid in plasma is reduced without exposing the urinary tract to an excessive load of uric acid, thus decreasing the risk of crystalluria. By lowering the uric acid concentration in plasma below its limits of solubility, allopurinol facilitates dissolution of tophi. Indications: The treatment of gout, either primary, or secondary to hyperuricemia which occurs in polycythemia vera, myeloid metaplasia or other blood dyscrasias. Allopurinol is also indicated in the treatment of primary or secondary uric acid nephropathy, with or without accompanying symptoms of gout. Allopurinol may be useful in patients with gouty nephropathy, in those who form renal urate stones, and in those with unusually severe disease. Allopurinol may be given prophylactically to prevent tissue urate deposition or renal calculi as well as acute urate nephropathy and resultant renal failure in patients with leukemias, lymphomas or other malignancies who are receiving radiation therapy or antineoplastic drugs that will result in elevated serum uric acid concentrations. To prevent the occurrence and recurrence of uric acid stones and renal calcium lithiasis in patients with hyperuricemia and/or hyperuricosuria.
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