Allopurinol (1H-pyrazolo[3,4-d]pyrimidin-4-ol) (Fig. 1) is a commonly used drug in the treatment of chronic gout or hyperuricaemia associated with leukaemia, radiotherapy, antineoplastic agents and treatment with Allopurinol is a structural isomer of hypoxanthine (a naturally occurring purine in the body) and acts to inhibit xanthine oxidase. In the presence of xanthine oxidase, allopurinol will be converted to alloxanthine (Fig. 2), after that the formation of uric acid from xanthine and hypoxanthine will be inhibited | Journal of Physical Science Vol. 19 2 23-30 2008 23 Spectrophotometric Determination of Allopurinol in Tablet Formulation Wejdan Shakir Khayoon1 Mouyad Qassim Al-Abaichy2 Mohamed Jasim2 and Mohamad Affan Al-Hamadany2 1School of Chemical Sciences Universiti Sains Malaysia 11800 USM Pulau Pinang Malaysia department of Chemistry College of Science Baghdad University Al-Jaderya Baghdad Iraq Corresponding author wijdansh2007@ Abstract A new spectrophotometric method for the determination of allopurinol drug was investigated. The proposed method was based on the reaction of the intended drug with catechol and Fe II to form a blue soluble complex which was measured at Ảmax 580 nm. A graph of absorbance versus concentration shown that Beer s law was obeyed over the concentration range of 2-10 pg mT1 with molar absorptivity of x 1031 moT1 cm-1 and Sandell sensitivity of x 10 2 pg cm-. A recovery percentage of 100 with RSD of was obtained. The proposed method was applied successfully for the determination of allopurinol drug in tablets with a good accuracy and precision. The optimum condition for the color development has also been investigated. Keywords allopurinol spectrophotometric methods tablet 1. INTRODUCTION Allopurinol 1H-pyrazolo 3 4-d pyrimidin-4-ol Fig. 1 is a commonly used drug in the treatment of chronic gout or hyperuricaemia associated with leukaemia radiotherapy antineoplastic agents and treatment with Allopurinol is a structural isomer of hypoxanthine a naturally occurring purine in the body and acts to inhibit xanthine oxidase. In the presence of xanthine oxidase allopurinol will be converted to alloxanthine Fig. 2 after that the formation of uric acid from xanthine and hypoxanthine will be inhibited. This enzyme is responsible for the successive oxidation of hypoxanthine and xanthine resulting in the production of uric acid the product of human purine In addition to block uric acid production .