Solid-state characterization of novel active pharmaceutical ingredients: cocrystal of a salbutamol hemiadipate salt with adipic acid (2:1:1) and salbutamol hemisuccinate salt

The production of salt or cocrystalline forms is a common approach to alter the physicochemical properties of pharmaceutical compounds. The goal of this work was to evaluate the impact of anion choice (succinate, adipate, and sulfate) on the physicochemical characteristics of salbutamol forms. Novel crystals of salbutamol were produced by solvent evaporation: a cocrystal of salbutamol hemiadipate with adipic acid (salbutamol adipate, SA), salbutamol hemisuccinate tetramethanolate (SSU.MeOH), and its desolvated form (SSU). The crystalline materials obtained were characterized using thermal, X-ray, nuclear magnetic resonance, Fourier transform infrared spectroscopy, dynamic vapor sorption (DVS), and elemental analysis. The crystal forms of SA and SSU.MeOH were determined to be triclinic, (Pī), and monoclinic, (P2(1) /n), respectively. DVS analysis confirmed that SSU and SA do not undergo hydration under increased relative humidity. Both thermal and elemental analyses confirmed the stoichiometry of the salt forms. The aqueous solubilities of SA and SSU were measured to be 82 ± 2 mg/mL (pH 4.5 ± 0.1) and 334 ± 13 mg/mL (pH 6.6 ± 0.1), respectively. Measured values corresponded well with the calculated pH solubility profiles. The intrinsic dissolution rate of cocrystallized SA was approximately four times lower than that of SSU, suggesting its use as an alternative to more rapidly dissolving salbutamol sulfate.