Studies on the intestinal absorption mechanism of diazepam in rat

Aim: To investigate the absorption mechanism of diazepam in various intestinal segments. Methods: In situ recirculation and single-pass perfusion were used to study the absorption mechanism of diazepam in rats. The concentrations of diazepam in intestinal fluid was measured by HPLC, and the oil-water partition coefficient of diazepam was caculated. The effects of three kinds of surfactants (Labrasol, Tween-80 and sodium dodecyl sulfate) on the absorption and transport of diazepam were also studied. Results: The absorption rate of diazepamwas obviously influenced by pH of regurgitation fluid and intestinal segments. Diazepam was absorbed in the whole intestine. The absorption rate constant (K_a) was greater in duodenum and jejunum. K_a in duodenum, jejunum, ileum and colon were estimated to be (0.186 ± 0.006) h^-1, (0.170 ± 0.011) h^-1, (0.086 ± 0.023) h^-1 and (0.059 ± 0.012) h^-1, respectively, Labrasol and Tween-80 evidently enhanced the absorption of diazepam in intestine. Conclusion: The absorption of diazepam occured via the simple diffusion.