Thermodynamic Insights into Isoniazid Solubility in PEG 300 + Water Mixtures

Solubility studies are essential for developing more efficient dosing processes and systems. The solubility of INH in a mixture of PEG 300 (1) + water (2) was evaluated at various temperatures using UV/Vis spectrophotometry and the shaking flask method. Solubility increased by 150% at 288.15 K and 298% at 318.15 K, reflecting the temperature dependence of solubility when transitioning from pure water to pure PEG 300. Generally, the solubility of INH is an endothermic process favoured by entropy. Its affinity increases with PEG 300 proportion in the mixtures, transitioning from an enthalpic to an entropic mechanism as it approaches the pure solvent. Ultimately, it is concluded that PEG 300 acts as an excellent, eco-friendly cosolvent that could help to optimise more sustainable pharmaceutical systems.