The objective of this study was to investigate the impact of different hydrophobic ion pairs (HIP) on the oral bioavailability of the model drug octreotide in pigs.
Octreotide was ion paired with the anionic surfactants deoxycholate, decanoate and docusate differing in lipophilicity. These hydrophobic ion pairs were incorporated in self-emulsifying drug delivery systems (SEDDS) based on BrijO10, octyldodecanol, propylene glycol and ethanol in a concentration of 5 mg/ml. SEDDS were characterized regarding size distribution, zeta potential, stability towards lipase, log DSEDDS/release medium and mucus diffusion behavior. The oral bioavailability of octreotide was evaluated in pigs via LC-MS/MS analyses.
Most efficient ion pairing was achieved at a molar ratio of 1:3 (peptide: surfactant). SEDDS containing the octreotide-deoxycholate, -decanoate and -docusate ion pair exhibited a mean droplet size of 152 nm, 112 nm and 191 nm and a zeta potential of − 3.7, − 4.6 and − 5.7 mV, respectively. They were completely stable towards degradation by lipase and showed a log DSEDDS/release medium of 1.7, 1.8 and 2.7, respectively. The diffusion coefficient of these SEDDS was in the range of 0.03, 0.11 and 0.17 × 10− 9 cm2/s, respectively. In vivo studies with these HIPs showed no improvement in the oral bioavailability in case of octreotide-decanoate. In contrast, octreotide-deoxycholate and octreotide-docusate SEDDS resulted in a 17.9-fold and 4.2-fold higher bioavailability vs. control.
According to these results, hydrophobic ion pairing could be identified as a key parameter for SEDDS to achieve high oral bioavailability.