In Vitro Dissolution Profile of Nitazoxanide Oral Suspension: Applying an HPLC Method in Drug Solubility and Chemical Stability Studies, With a Direct Impact on In Vitro Release

Abstract

Nitazoxanide is a broad‐spectrum prodrug widely used against protozoa, helminthes, and anaerobic bacteria. Due to its hydrophobicity, this drug exhibits limited water solubility, making its release from the formulation critical. Furthermore, its rapid degradation into tizoxanide (the in vivo active form) requires analytical considerations to ensure reliable quantification during quality control. This study aimed to develop a discriminative in vitro dissolution test for nitazoxanide powder for oral suspension (20 mg/mL), comparing the reference product (Annita) with a commercially available generic formulation. Drug quantification was performed using a previously validated HPLC method. Solubility studies were conducted using various surfactants (sodium dodecyl sulfate, Tween 80, cetylpyridinium chloride) and specific pH values. Stability was monitored via HPLC and LC‐MS to assess the conversion of nitazoxanide into tizoxanide. Dissolution conditions were optimized based on the solubility and stability data. The optimized dissolution medium consisted of pH 7.4 phosphate buffer with 5% cetylpyridinium chloride, using USP Apparatus 2 (paddles) at 100 rpm and 37°C. This method achieved 100% dissolution for both products within 60 min and demonstrated discriminative potential (similarity factor f 2 = 32.90). The study confirmed the rapid conversion of nitazoxanide into tizoxanide in alkaline media, requiring careful attention during drug quantification to ensure the reliability of the analytical results. Thus, the proposed dissolution test was successfully developed, incorporating a detailed experimental analysis of how drug solubility and stability influence in vitro release, thereby allowing for a deeper exploration of solubility and chemical stability aspects.