Methods: Oseltamivir uptake profile and its inhibition with excess peptides were examined by using Caco-2 and HeLa cells stably expressing human PEPT1 (HeLa/ PEPT1). To examine the contribution of PEPT1 in gastrointestinal absorption of oseltamivir in vivo, simultaneous administration of casein, glycyl-sarcosine (Gly-Sar) and milk with oseltamivir was conducted in rats. We also evaluated the effect of milk on the pharmacokinetics of oseltamivir in healthy volunteers. The predictability of the extent of milk inhibition of intestinal oseltamivir absorption in humans was examined by using duodenal transit time and inhibitory rate by excess peptides in Caco-2 cells.
Results: Oseltamivir uptake by Caco-2 and HeLa/ PEPT1 cells were temperature- and concentration-dependent (Km = 6.5 mM and 8.6 mM, respectively) and one-half to two-third was inhibited by PEPT1 inhibitors such as 10 mM Gly-Sar or Trp-Gly. Plasma concentration of oseltamivir after oral administration in rats was greatly decreased by milk (62%), casein (82%) and 125 mM Gly-Sar (82%) compared with the control group. Plasma concentration of oseltamivir was lower in humans from time 0 to 2hrs, when taken with milk, while AUC0-∞was not affected significantly. Urinary excretion of oseltamivir and active metabolite Ro 64-0802 was decreased to 78% of control by milk. The prediction was roughly consistent with the observed value for the inhibitory ratio of milk for oseltamivir absorption in humans.
Conclusions: Our in vitro study suggested that the gastrointestinal absorption of oseltamivir was mediated by PEPT1 at least in part and inhibited by dietary peptides. In vivo pharmacokinetic study confirmed that intestinal absorption of oseltamivir was interacted with milk peptides in both rats and humans, while the extent of the inhibition was different. This may be due to differences in the regional expression and the contribution of PEPT1 on the gastrointestinal absorption of oseltamivir between rats and humans.