(T1130-01-02) In Vitro Digestion-Diffusion Model for Predicting In Vivo Performance of Lipid-Based Formulations

Purpose: Lipid-based formulations (LBFs) are known as successful products to improve oral absorption of poorly water-soluble drugs by circumventing the dissolution process from a solid state in the GI tract [1,2]. However, LBFs account for a small percentage of pharmaceutical products in the market. The main reason for the paucity of LBFs in the market is the lack of mechanistic and quantitative models that can predict drug release from LBFs under conditions mimicking the GI environment, with only a few studies on the in vitro-in vivo correlation (IVIVC) of LBFs [3,4]. The purpose of this study was to predict in vivo performance of LBFs using data from the in vitro Franz diffusion cell system. This system needs only a small amount/volume of formulation on the donor side (≈ 1 g/1 mL), which allows us to screen formulations in an early development phase. First, the in vivo oral absorption in rats and in vitro dissolution profiles of a BCS Class II drug formulated in three different LBFs were determined. Then, in vitro permeation during the digestion of LBFs was evaluated using a Franz diffusion cell that contained a dialysis membrane. Finally, in vitro dissolution and permeation profiles for all LBFs were compared with in vivo systemic exposure to assess the predictive accuracy of the in vitro Franz diffusion cell for LBFs.

Methods: As model LBFs, the type IIIA-MC (30% [w/w] Captex 300, 30% Capmul MCM, 40% Kolliphor EL), type IIIB-MC (10% Captex 300, 10% Capmul MCM, 60% Kolliphor EL, 20% Transcutol HP), and type IV (50% Kolliphor EL, 50% Transcutol HP) formulations were prepared. Fenofibrate (FEN) was selected as a model drug and loaded at 60 mg/g into each LBF. For in vivo studies, FEN formulated into each LBF was orally administered to rats at 6.0 mg/kg (dose concentration: 1.5 mg/mL), and blood samples were collected over 24 h. In the in vitro studies, each LBF was dispersed in simulated intestinal fluid (pH 6.5) at a final concentration of 1.5 mg/mL, equivalent to that used in the in vivo study. Five minutes after dispersing the LBF, a pancreatic lipase solution was added to initiate lipid digestion, and 1 mL of this solution was immediately applied to the donor side of the Franz diffusion cell. Samples were collected from the receiver side filled with HBSS containing 4.5% BSA. Also, the dissolved concentration of FEN was observed after initiating digestion. FEN concentration was analyzed using HPLC or LC-MS/MS. The area under the dissolved concentration- and plasma concentration-time curves (AUC_dissolved and AUC_plasma) were calculated using the trapezoidal method.

Results: In the in vivo oral study, all LBFs showed similar plasma concentration-time profiles for fenofibric acid, a metabolite of FEN, showing no significant differences in AUC_plasma, C_max, and T_max. This result was consistent with the reported data [5]. In contrast, in vitro dissolution study, the type IIIA-MC formulation showed a significantly lower dissolved concentration of FEN than the type IIIB-MC and type IV formulations throughout the experiment. Type IIIB-MC and type IV formulations showed similar dissolved concentration-time profiles. The calculated AUC_dissolved value for type IIIA formulation was approximately 3-fold lower than those for the type IIIB-MC and type IV formulations. This result indicated that the medium-chain lipids composed of the type IIIA-MC (lipid-rich) formulation were quickly digested, its solubilization capacity dropped, and FEN ultimately precipitated. In contrast, both type IIIB-MC and IV (both surfactant-rich) formulations were less digestible by pancreatin, maintaining high solubilazation capacity throughout the experiments. In general, the dissolved concentration is the sum of the solubilized concentration in the lipid droplets and the free concentration in the bulk aqueous phase. Therefore, the dissolved concentration-time profile and its AUC_dissolved value might not predict in vivo performance of LBFs. In the in vitro release study, all LBFs showed similar permeated amount-time profiles. These results were in good agreement with the current in vivo results. Thus, the Franz diffusion cell mounted with the dialysis membrane would successfully detect the free drug released from LBFs. The release study revealed that free FEN concentrations in the bulk aqueous phase were almost the same for all LBFs, while the dissolution study showed large differences in the solubilized concentrations between lipid-rich (type IIIA-MC) and surfactant-rich (type IIIB-MC/IV) formulations during lipid digestion. This discrepancy indicated the importance of detection of free drug, which can permeate the dialysis membrane/epithelium cells.

Conclusion: The findings indicated that in vitro Franz diffusion cell mounted with the dialysis membrane would help predict the in vivo performance and establish an IVIVC of LBFs in an early development phase.

References: [1] Adv Drug Deliv Rev. 60 (2008) 625-637.
[2] Adv Drug Deliv Rev. 101 (2016) 167-194.
[3] Acta Pharm Sin B. 11 (2021) 2469-2487.
[4] AAPS J. 16 (2014) 539-549.
[5] Pharm Res. 33 (2016) 970-982.