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Simultaneous determination of allopurinol and benzbromarone in presence of the active metabolite oxipurinol

Marianne Nebsen, Mohamed K.Abd El-Rahman, Maissa Y.Salem, Mohamed G.El-Bardicy, Amira M.El-Kosasy

Simple, sensitive, selective and precise spectrophotometric, spectrodensitometric and HPLCmethods were developed and validated for the simultaneous determination of allopurinol (AL)&benzbromarone (BZ) in presence of oxipurinol (OX) which is the active metabolite ofAL. In the spectrophotometric methods, BZ was determined by the application of direct spectrophotometry and measuring its zero-order (D0) absorption spectra at its ëmax=356 nm.ALwas determined bymeasuring the peak amplitude of the second derivative curve (D2) at 281.4 nm or by measuring the peak amplitude of the second derivative of the ratio spectra curve (DD2) at 282.4 nmafter using a spectrumof 8ug/ml BZ as a divisor. The TLC-densitometric method depends on the difference in Rf values using acetone: chloroform: NH3 (5: 4: 0.01 v/v/v) as a mobile phase. The spots of the two drugs were scanned at 250 and 356 nm. The HPLCmethod was based on the separation of the drugs on a reversed phase column using a mobile phase of 0.01 M phosphate buffer pH: 4.0- acetonitrile-methanol (50:30: 20 v/v/v) with UV detection of the effluent at 250 nm. The proposed methods were used to determine both drugs in their pure powder formand in pharmaceutical dosage forms.