*Article* **Lidocaine Pharmaceutical Multicomponent Forms: A Story about the Role of Chloride Ions on Their Stability**

**Cristóbal Verdugo-Escamilla 1,\*, Carolina Alarcón-Payer 2, Francisco Javier Acebedo-Martínez 1, Raquel Fernández-Penas 1, Alicia Domínguez-Martín 3,\* and Duane Choquesillo-Lazarte <sup>1</sup>**


**Abstract:** In this investigation, three new crystal forms of lidocaine, and another three of lidocaine hydrochloride with hydroquinone, resorcinol, and pyrogallol were synthetised. All the new forms were characterised using multiple techniques, PXRD, SC-XRD, DSC, and FTIR. The stability of the forms was studied, and, for the more stable forms, i.e., **(lidhcl)** forms, the solubility was determined through FTIR analysis. The new crystalline forms obtained with **(lidhcl)** and the three coformers showed an interesting steric stabilisation mechanism of the oxidation of hydroxybenzenes and showed good physicochemical properties with respect to **(lidhcl)**, constituting a mechanism of modulation of the physicochemical properties.

**Keywords:** lidocaine; cocrystals; mechanochemistry; multicomponent materials; API; pharmaceutical solids; solubility
