Investigating the Relationship between In Vitro and In Vivo Performance: The Role of Drug Loading, Release Rate, and
Emily G Benson1, Hitesh S Purohit2, Geoff G Z Zhang2
1Department of Industrial and Molecular Pharmaceutics, College of Pharmacy, Purdue University, West Lafayette, Indiana 47907, United States.
Molecular Pharmaceutics
|March 19, 2026
Summary
Amorphous solid dispersions (ASDs) with hypromellose (HPMC) show improved drug release and absorption. Higher drug loading impacts phase separation and release rates, but still outperforms crystalline forms.
Area of Science:
- Pharmaceutical Sciences
- Materials Science
- Drug Delivery
Background:
- Amorphous solid dispersions (ASDs) enhance oral absorption of poorly water-soluble drugs.
- Hypromellose (HPMC) is a common polymer in ASDs, but its drug release mechanisms are not fully understood.
- Tacrolimus/HPMC ASDs were investigated to elucidate these mechanisms.
Purpose of the Study:
- To investigate the morphology of phase separation in tacrolimus/HPMC ASDs using confocal fluorescence microscopy (CFM).
- To evaluate the in vitro and in vivo release and absorption performance of ASDs at various drug loadings (DL).
- To correlate formulation performance with drug release mechanisms and morphology.
Main Methods:
- Confocal fluorescence microscopy (CFM) to visualize phase separation morphology.
- In vitro release studies measuring drug and polymer release rates.
- In vivo pharmacokinetic studies in fasted dogs.
Main Results:
- At 10% DL and above, a drug-rich network formed, with HPMC diffusing into the solution.
- HPMC release was 10x faster than tacrolimus at 10% DL, while congruent at 5% DL.
- ASDs demonstrated significantly improved in vivo absorption compared to crystalline tacrolimus, especially at 10% and 50% DL.
Conclusions:
- CFM revealed distinct phase separation morphologies influencing drug release.
- Drug release rates and supersaturation extent varied with drug loading.
- Tacrolimus/HPMC ASDs offer superior oral absorption compared to crystalline forms, with potential for further optimization.
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