Enhancement of the solubility and oral bioavailability of altrenogest through complexation with hydroxypropyl-β-cyclodextrin

Altrenogest (ALT), a synthetic progestogen, serves a critical role in estrus synchronization among animals like gilts and mares. However, its practical application in animal husbandry is hampered due to its poor solubility and limited oral bioavailability. To address this challenge, a solvent evaporation method was employed to create an inclusion complex of ALT with hydroxypropyl-β-cyclodextrin (ALT/HP-β-CD). The formation of this inclusion complex was confirmed by scanning electron microscopy, power X-ray diffraction, differential scanning calorimetry, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, and docking calculations. In addition, we further conducted pharmacokinetic investigation involving gilts, comparing ALT/HP-β-CD inclusion complex to an ALT oral solution. The physicochemical characterization results unveiled a transformation of ALT's crystal morphology into an amorphous state, with ALT effectively entering the cavity of HP-β-CD. Compared with ALT, the solubility of ALT/HP-β-CD inclusion complex increased by 1026.51-fold, and its dissolution rate demonstrated significant improvement. Pharmacokinetic assessments further revealed that the oral bioavailability of ALT/HP-β-CD inclusion complex surpassed that of the ALT oral solution, with a relative bioavailability of 114.08 %. In conclusion, complexation with HP-β-CD represents a highly effective approach to improve both the solubility and oral bioavailability of ALT.