Purpose. The purpose of this work was to determine the jejunal permeability of cyclosporin A (CsA) in humans and whether formulation variables modulate the effects of P‐glycoprotein (P‐gp) on the permeability of CsA in Caco‐2 cells.
Methods. A solution containing CsA, phenylalanine, propranolol, polyethyleneglycol (PEG) 400, and PEG 4000 was perfused through a 10‐cm jejunal segment in 12 subjects. Caco‐2 transport studies were performed using previously reported methodology.
Results. The mean Peff (±SD) of CsA in humans was 1.65 (0.53). The mean permeabilities for phenylalanine, propranolol, and PEG 400 were 4.54 (2.39), 2.90 (1.28), and 0.83 (0.51) × 10\‐4 cm/s, respectively. The presence of surfactants significantly decreased the permeabilities of CsA in both directions in Caco‐2 cells.
Conclusions. The results suggest that the effects of surfactants via micellar solubilization and inhibition of P‐gp efflux on CsA transport in Caco‐2 cells are significant. CsA can rightly be classified as a low solubility‐high permeability Class II BCS drug and its highly variable absorption from Sandimmune® oral formulations is the result of poor dissolution characteristics.
