The objective of this study was to build a novel method to control gastric acidity under fasting condition for evaluating the bioavailability of an oral formulation in dogs. As a method for controlling gastric acidity, pretreatments by intramuscular pentagastrin administration, oral hydrochloric acid administration and oral water administration were examined. Pentagastrin and hydrochloric acid pretreatments insufficiently decreased the gastric pH, in some cases, with the remaining contents in the stomach, i.e. feces or highly viscous mucus, to possibly prevent lowering of the pH as a cause. On the other hand, pretreatment by administration of water could successfully achieve two objectives: elimination of gastric contents and acidity control by increasing gastrointestinal peristalsis and gastric acid secretion. A comparative bioavailability study of orally dosed cinnarizine, which is a weakly basic drug with a pH-dependent solubility, conducted by water pretreatment in dogs showed a significantly higher plasma concentration-time profile than that in not-acidified dogs pretreated by a proton pump inhibitor, omeprazole dosed intravenously. This result confirmed the validity of the pretreatment by oral water as a method to control the gastric acidity in dogs. A simple and safe method for controlling gastric acidity without placing an excessive load on the dog by only administering water, which utilizes the physiological functions of animals, is considered highly reproducible and useful as a model for evaluating the bioavailability of oral formulations.

The aim of this study is to clarify the effect of hydrophilic ethylene oxide (EO) chain length in steareths on the physicochemical characteristics, gene expression efficiency and cytotoxicity of plasmid DNA (pDNA)/poly-L-ornithine (PLO)/niosomes (consisting of non-ionic surfactants [NISs], polyoxyethylene stearyl ethers [steareths]) ternary complexes. Niosomes were prepared with NISs, a series of steareth (steareth-2, steareth-5 and steareth-20) or Tween 80, cholesterol, and octadecylamine of cationic lipid, followed by complexing with pDNA encoding luciferase gene and PLO. The physicochemical characteristics, gene expression efficiency and cytotoxicity of the prepared pDNA/PLO/niosome ternary complexes were evaluated. The particle size and ζ potential of steareth niosomes and pDNA/PLO/steareth niosome ternary complexes decreased with lengthening of the EO chain in steareth. All complexes showed a high pDNA condensation ability, and pDNA/PLO/steareth-2 niosome ternary complexes possessed the highest protective effect in the presence of polyanion, dextran sulfate. The transfection efficiency and cell viability of pDNA/PLO/steareth niosome ternary complexes also decreased with the lengthening of the EO chain. Among the pDNA/PLO/niosome ternary complexes, the pDNA/PLO/steareth-2 niosome ternary complexes showed the highest transfection efficiency and almost no cell damage. In conclusion, it was suggested that the EO chain length in steareths affects the physicochemical characteristics, gene expression efficiency and cytotoxicity of pDNA/PLO/steareth niosome ternary complexes. Furthermore, we pointed out that the pDNA/PLO/steareth-2 niosome ternary complexes might deliver genes efficiently and safely. Further study is required to more elevate the transfection efficiency, stability and safety of pDNA/PLO/steareth-2 niosome ternary complexes, such as using target compounds.