*Article* **Application of Sucrose Acetate Isobutyrate in Development of Co-Amorphous Formulations of Tacrolimus for Bioavailability Enhancement**

**Eman M. Mohamed 1,2, Sathish Dharani 1, Mohammad T. H. Nutan 3, Phillip Cook 4, Rajendran Arunagiri 4, Mansoor A. Khan <sup>1</sup> and Ziyaur Rahman 1,\***


**Abstract:** The focus of the present work was to develop co-amorphous dispersion (CAD) formulations of tacrolimus (TAC) using sucrose acetate isobutyrate as a carrier, evaluate by in vitro and in vivo methods and compare its performance with hydroxypropyl methylcellulose (HPMC) based amorphous solid dispersion (ASD) formulation. CAD and ASD formulations were prepared by solvent evaporation method followed by characterization by Fourier transformed infrared spectroscopy, X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), dissolution, stability, and pharmacokinetics. XRPD and DSC indicated amorphous phase transformation of the drug in the CAD and ASD formulations, and dissolved more than 85% of the drug in 90 min. No drug crystallization was observed in the thermogram and diffractogram of the formulations after storage at 25 ◦C/60% RH and 40 ◦C/75% RH. No significant change in the dissolution profile was observed after and before storage. SAIB-based CAD and HPMC-based ASD formulations were bioequivalent as they met 90% confidence of 90–11.1% for Cmax and AUC. The CAD and ASD formulations exhibited Cmax and AUC 1.7–1.8 and 1.5–1.8 folds of tablet formulations containing the drug's crystalline phase. In conclusion, the stability, dissolution, and pharmacokinetic performance of SAIB-based CAD and HPMC-based ASD formulations were similar, and thus clinical performance would be similar.

**Keywords:** tacrolimus; sucrose acetate isobutyrate; amorphous solid dispersion; dissolution; stability; pharmacokinetics
