**4. Conclusions**

This study investigates the encapsulation of antipsychotic drug RSP by RM-β-CD and the compatibility of the inclusion complex with several excipients commonly used in pharmaceutical dosage forms. The RSP/RM-β-CD binary product was obtained using the kneading method and was evaluated by experimental and theoretical approaches. The experimental results provided by thermal methods, powder X-ray diffractometry, and UATR-FTIR spectroscopy demonstrate the inclusion complex formation between RSP and RM-β-CD in 1:1 molar ratio as the solubility studies indicated. As a result of inclusion complex formation, the RSP solubility was increased by 2.58-fold as compared with free RSP, highlighting the solubilizing effect of CD.

Since the corroboration of thermoanalytical data suggested that the inclusion complex is compatible with three of the selected excipients (namely STR, CEL, and MgSTE), but incompatible with LCT, two complementary investigational tools were used, namely UATR-FTIR spectroscopy and PXRD. These last two instrumental techniques allow the evaluation of compatibility/incompatibility between the components of a complex matrix in ambient conditions. It was shown that interactions between the RSP/RM-β-CD and LCT occur in solid state even under ambient conditions, and they are accentuated by the thermal stress. In the development of new generic forms containing RSP formulated as a supramolecular adduct with RM-β-CD, precautions should be taken in the selection of excipients, without using lactose in the final product.

**Author Contributions:** Conceptualization, L.S., I.-M.T., A.L., O.S. and I.L.; data curation, I.-M.T.; formal analysis, A.L. and D.C.; investigation, L.S., I.-M.T., A.L., G.V., P.B., M.M., R.-M.V. and O.S.; methodology, L.S., G.V., R.-M.V. and I.L.; project administration, L.S.; resources, I.-M.T., D.C., G.V., P.B. and M.M.; software, R.-M.V.; supervision, A.L. and I.L.; validation, I.-M.T., A.L., O.S. and I.L.; visualization, A.L., D.C. and G.V.; writing—original draft, L.S., I.-M.T. and O.S.; writing—review and editing, L.S., A.L., O.S. and I.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.

**Sample Availability:** Samples of the compounds are available in limited quantity from the authors.
