Buspirone Hydrochloride Polymorphism: Stability, Solubility, Flow Properties, and Manufacturing Implications

Area of Science:

• Pharmaceutical Sciences
• Solid-State Chemistry
• Drug Development

Background:

• Buspirone hydrochloride, an anxiolytic, exists in two interconvertible polymorphic forms.
• Polymorphism significantly influences drug physicochemical properties and therapeutic efficacy.
• Neglecting polymorphism in pharmaceutical analysis can lead to inconsistent results and compromised drug performance.

Purpose of the Study:

• To investigate the polymorphism, stability, solubility, and flow properties of commercial buspirone hydrochloride samples.
• To understand how polymorphic transformations affect pharmaceutical performance.
• To identify the most effective analytical methods for distinguishing polymorphic forms.

Main Methods:

• Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and powder X-ray diffraction (PXRD) for structural characterization.
• Carr index and Hausner ratio for flow and density properties.
• High-performance liquid chromatography (HPLC) for solubility evaluation in physiologically relevant pH media.

Main Results:

• Commercial samples showed variations: one contained a mixture of Form 1 and Form 2, the other exclusively Form 2.
• Form 2 converted to the more thermodynamically stable Form 1 under stress conditions (humidity and temperature).
• DSC was the most effective method for distinguishing polymorphic forms and identifying mixtures; both forms exhibited poor flow properties and pH-dependent solubility.

Conclusions:

• Buspirone hydrochloride Form 1 demonstrates greater thermodynamic stability than Form 2.
• Polymorphic transformations and poor flow properties necessitate formulation adjustments for effective drug delivery.
• Findings support preliminary Biopharmaceutics Classification System (BCS) Class I or III classification, pending permeability studies.