Pharmaceutical salt of isoniazid-orotic acid with optimized solubility, dissolution rate, and tabletability

Isoniazid (INH) is a first-line antitubercular drug characterized by its high solubility and rapid absorption following oral administration, which poses challenges in maintaining sustained therapeutic concentrations. To address this issue, we have developed a novel pharmaceutical salt of INH with orotic acid (OA). Single-crystal Xray diffraction (XRD) analysis revealed that intermolecular proton transfer occurs between the carboxyl group of OA and the pyridine nitrogen site of INH, resulting in a salt comprising INHH+ cations and OA- anions. Solubility and dissolution studies indicated that INH-OA exhibits significantly reduced solubility and decelerated intrinsic dissolution rate (IDR). Specifically, solubility reductions were observed to be 74.24% in pH 1.2 HCl solution and 90.29% in pH 6.8 phosphate buffer solution. The IDR of the salt was found to be 2.62% and 0.96% of that of pure INH in pH 1.2 and pH 6.8 aqueous media, respectively. Additionally, INH-OA demonstrated improved tablet- ability. These findings suggest that the formation of this salt significantly enhances the pharmaceutical properties of INH.