Purpose: The development of in vitro- in vivo correlation (IVIVC) has remained a huge challenge for the complex parenteral controlled release drug products such as microspheres. Nevertheless, we have recently developed level A IVIVC for microspheres containing small molecule hydrophobic drugs such as Naltrexone and Risperidone1,2. In order to further explore the concept of development of IVIVC for microspheres containing hydrophilic molecules, especially large molecule such as peptides, the present study was conducted to understand challenges involved and possibility of establishing level A IVIVCs for such products.
Methods: Leuprolide acetate (LA) was chosen as a model peptide and PLGA with similar molecular weight to that of the commercial product Lupron Depot® (one month) was used to prepare LA microspheres. Different process parameters (e.g. solvent system, homogenization speed) were investigated in order to obtain compositionally equivalent LA microspheres with manufacturing differences. Critical quality attributes (e.g. drug loading, particle size, porosity, morphology etc.) of the prepared microspheres were investigated. Furthermore, in vitro release testing of the prepared LA microspheres was conducted using a sample-and-separate method. In vivo release testing was conducted using rabbit model and collected plasma samples were analysed using LC-MS. The in vivo plasma concentration vs time profiles were deconvoluted using Loo-Riegelman method and used to establish the IVIVC. Developed IVVICs were validated by determination of % prediction error (PE) using WinNonlin 6.4, PK/PD software.
Results: Despite the differences in the manufacturing processes, all the prepared LA microsphere formulations had similar peptide loading (8.5%, w/w) and hence, compositionally equivalent. However, differences in critical quality attributes such as particle size, porosity and drug distribution was observed due to minor changes in manufacturing processes. This in turn resulted in alteration of drug release characteristics such as %burst release and release rates. For example, formulation F1, prepared using methylene chloride (DCM) and methanol, had low burst release compared to formulation F3 that was prepared using DCM and dimethyl sulfoxide (DMSO). This might be because of the differences in the solubility of PLGA polymer and peptide in different cosolvent systems, leading to differences in polymer solidification and drug diffusion rate. Moreover, formulations prepared using the same solvent system but with weaker emulsification force had larger particle size (Figure 1) and hence, slower release rate. The overall in vitro-release profiles of peptide microspheres were biphasic with burst release phase followed by slow and continuous release, which is significantly different than that of microspheres containing hydrophobic drug (lag phase, slow release and fast release1,2. The sample-and separate in vitro release testing method was able to differentiate changes in the release characteristics of the prepared peptide microsphere formulations (Figure 2). Similar differences were observed in the in vivo release profiles with relatively lower burst release compared to the respective in vitro release profiles (Figure 3). This might be because of the less permeability of the hydrophilic peptide, which results in the lower plasma concentration and hence, low burst release. A level A IVIVC was established between fraction release in vitro and fraction absorbed in vivo using time scaling. The % PE of the developed IVIVC was acceptable (<10% for Cmax and AUC)) as per U.S.FDA guideline4.
Conclusion: Despite the differences in the in vitro and in vivo release profiles (% burst release and release rate), an affirmative level A IVIVC was developed using the developed in vitro release testing method in a rabbit model for peptide microspheres.
The present work together with our previous work on the development of IVIVC1.2 shows that it is possible to develop IVIVC for variety of parenteral controlled release microsphere drug products with differences in critical quality attributes and release profiles.
Jie Shen– Assistant Professor, University of Rhode Island, kingston, Rhode Island
Yuan Zou– Staff Fellow, United States Food and Drug Administration
Yan Wang– Staff Fellow, United States Food and Drug Administration
Stephanie Choi– Chemist, US Food and Drug Administration, Maryland
Diane Burgess– Distinguished Professor of Pharmaceutics, University of Connecticut, Storrs, Connecticut