(T1430-06-35) Investigation of In Vitro Buccal Permeation Mechanisms of Compound A

Purpose: Buccal delivery is an attractive administration route since therapeutics get absorbed mainly through the buccal mucosa, which bypasses enzymatic degradation in the gastrointestinal tract as well as the hepatic first-pass metabolism. Understanding drug buccal permeation mechanisms is important for formulation development. In vitro permeation test (IVPT) using buccal mucosal tissues has been commonly used in selection of new chemical entities and formulation development. The objective of the present study was to identify key parameters that can affect buccal permeation of a basic compound A.

Methods: The in vitro permeation studies were conducted using a vertical diffusion cell (VDC) apparatus with a 0.38 cm² contact area. Porcine buccal tissues were used as the model membrane. Different parameters such as concentration and pH on the buccal permeation of compound A were studied. Antioxidants (i.e., 0.1% L-ascorbic acid (AA) and 0.1% sodium metabisulfite (SA)) were added in the media to stabilize compound A. Phosphate buffer (0.02 M, pH 6.8) containing 0.1% AA and 0.1% SA was utilized as the receptor medium. The study duration was kept at 12 hours to ensure that the integrity of the buccal mucosal tissues was well maintained. Receptor media were taken at pre-determined time points and analyzed using a validated high performance liquid chromatography (HPLC) method. The animal tissue integrity was monitored before and after IVPT by measuring the thickness of buccal tissues and histopathological staining via hematoxylin and eosin (H&E)

Results: As shown in Figure 1a, the IVP flux of compound A under the pH (6.8) of the artificial saliva fluid was enhanced with increase in drug concentration from 0.44 mg/mL to a saturated concentration (1.91 mg/mL). The cumulative drug permeation amount over 12 hours showed a good correlation (R²>0.97) to the drug concentration (Figure 1b). In addition, the permeation flux was enhanced when pH was increased from 4.7 to 6.8 when tested at 0.9 mg/mLconcentration (Figure 2a). The pH impact from pH 6.8 to pH 7.4 was studied at a lower concentration (0.45 mg/mL) due to the limited solubility of compound A at neutral pH. Further increasing pH from 6.8 to 7.4 did not result in significant buccal permeation change (Figure 2b). The permeation coefficient was calculated and showed in Table 1.

Conclusion: A validated IVPT method via a VDC apparatus using excised buccal tissues can assist in understanding of drug permeation through the buccal mucosa. Our study demonstrated that there was a linear correlation between the dosed compound A concentration to the cumulative permeated drug amount, which indicated that the permeation of compound A through the buccal mucosa is dominated by passive diffusion. At higher pH’s (up to pH 6.8), unionized fraction of compound A was increased, resulting in enhanced buccal permeation. This result indicated that compound A permeation through the buccal mucosa was mainly through the transcellular route. Since the unionized fraction of compound A did not have a significant increase from pH 6.8 to 7.4, drug permeation was similar under these pH conditions. Our study successfully elucidated the permeation mechanisms of compound A through the buccal mucosa. The knowledge obtained will be used to assist in future product development.

Acknowledgments: This project was supported by SUNOVION Pharmaceuticals.

Figure 1. (a) In vitro permeation flux profiles of compound A with different concentrations at pH 6.8 (mean ± S.D.) and (b) correlation between the cumulative permeated drug amount over 12 hours and dosed drug concentration (mean ± S.D.).



Figure 2. In vitro permeation flux profiles of compound A under different pH’s at concentrations of (a) 0.9 mg/mL and (b) 0.45 mg/mL (mean ± S.D.).



Table 1. Permeation coefficient of compound A at different pH’s and concentrations (mean ± S.D.).