Oral Delivery of a Renin Inhibitor Compound Using Emulsion Formulations

The oral delivery of O-(N-morpholino-carbonyl-3-L-phenylaspartyl-L-leucinamide of (2S,3R,4S)-2-amino-l-cyclohexyl-3,4-dihydroxy-6-methylheptane (I), a new renin inhibitor, was studied in the in vivo rat model using emulsion formulations. The components of the emulsion formulations were chosen based on their proposed effects on membrane structure, membrane fluidity, and solute transport. The percent absolute bioavailability (%AB) of I was increased from 0.3% (water suspension) to 5.1% when long-chain unsaturated fatty acid (oleic acid, linoleic acid, etc.)- and mono- and diglyceride (monolein, dilaurin, etc.)-containing emulsion formulations were used. Considering very high first-pass liver extraction of the compound (80%), it is suggested that emulsion formulations increased the intestinal transport of the compound significantly. The solubility of I in aqueous media with and without bile salt (20 mM) was found to be low (~1 µg/ml). Incubation in 0.01 N HC1 did not affect the particle size of the emulsion. The titration of oleic acid/monoolein emulsion in a pH 6.5 medium with a mixed bile salt system indicated reduction in the particle size of the emulsion. Drug precipitation was observed above 30 mM bile salt concentrations. No drug crystals could be detected in the intestinal contents of the rats when emulsion formulations were ingested. These results suggest that in the intestine of the animals, the particle size of the emulsions is reduced in the presence of bile fluid while the drug resides primarily in the oil phase. The mechanism of enhanced transport of I from the emulsion formulations is discussed along with the possibility of cotransport for the drug and oil. Emulsion formulations can be a potential delivery form for low-bioavailable lipid-soluble drugs.