Forced Degradation and Stability-Indicating Study for the Binary Mixture of Allopurinol and Thioctic Acid Using Validated HPLC-DAD Method.

Background: Careful review of the scientific databases revealed that no stability-indicating analytical method is available for the binary mixture of allopurinol (ALO) and thioctic acid (THA).
Objective: A comprehensive stability-indicating HPLC-DAD procedure has been executed for concurrent analysis of ALO and THA.
Method: Successful chromatographic separation of the cited drugs was reached using a Durashell C18 column (4.6 × 250 mm, 5 µm particle size). The mobile phase consisted of a mixture of acidified water (pH 4.0) using phosphoric acid and acetonitrile pumped in gradient elution mode. For quantification of ALO and THA, their respective peak areas were recorded at 249 and 210 nm. A systematic validation of analytical performance was investigated in terms of system suitability, linearity, ranges, precision, accuracy, specificity, robustness, detection, and quantification limits.
Results: ALO and THA peaks emerged at retention times 4.26 and 8.15 min, respectively. Linear ranges for ALO and THA were 5-100 and 10-400 µg/mL, respectively, with correlation coefficient values exceeding 0.9999. Both drugs were exposed to conditions of neutral, acidic, and alkaline hydrolysis, oxidation, and thermal decomposition. Stability-indicating features have been demonstrated by resolution of the drugs from their forced degradation peaks. For verification of peak identity and purity, the diode-array detector (DAD) was used. In addition, degradation pathways for the cited drugs were postulated. Furthermore, separation of both analytes from about 13 medicinal compounds of different therapeutic classes disclosed optimum specificity of the proposed method.
Conclusions: Advantageous application of the validated HPLC method for the concurrent analysis of ALO/THA in their tablet dosage form was accomplished.
Highlights: So far, the described HPLC-DAD method is considered the first detailed stability-indicating analytical study for this pharmaceutical mixture.
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