Elucidation of Degradation Behavior of Nitrazepam and Other Benzodiazepines in Artificial Gastric Juice: Study on Degradability of Drugs in Stomach (II).

The degradation behavior of eight benzodiazepines (BZPs): alprazolam, etizolam, diazepam, triazolam, nitrazepam (NZP), flunitrazepam (FNZ), bromazepam, and lorazepam, in artificial gastric juice was monitored by a LC/photodiode array detector (PDA) to estimate their pharmacokinetics in the stomach. For drugs that were degradable, such physicochemical parameters as reaction rate constant were measured to evaluate the effect of storage conditions on drug degradability, such as whether the degradation proceeds faster by increasing storage temperature, or whether the degradation reaction is reversible by adjusting pH. As a result, it was confirmed that although the eight BZPs degraded in artificial gastric juice, most of them could be restored when pH was increased, and the restoration rates differed depending on the pH and the type of BZP. As for NZP, an Arrhenius plot was drawn to obtain the physicochemical parameters, such as activation energy and activation entropy involved in the degradation reaction, and the reaction kinetics was discussed. In addition, two substances were confirmed as the degradation products of NZP in artificial gastric juice: one was a reversible degradation product (A) (intermediate) and the other was an irreversible degradation product (B) (final degradation product). The intermediate was identified as 2-amino-N-(2-benzoyl-4-nitrophenyl)-acetamide, and the final degradation product was 2-amino-5-nitrobenzophenone. Therefore, when detecting NZP in human stomach contents, such as during judicial dissection, it would be prudent to target NZP as well as the intermediate (A) and the final degradation product (B).

Evaluation of a thiodipeptide, L-phenylalanyl-Ψ[CS-N]-L-alanine, as a novel probe for peptide transporter 1.

L-Phenylalanyl-Ψ[CS-N]-l-alanine (Phe-Ψ-Ala), a thiourea dipeptide, was evaluated as a probe for peptide transporter 1 (PEPT1). Uptake of Phe-Ψ-Ala in PEPT1-overexpressing HeLa cells was significantly higher than that in vector-transfected HeLa cells and the Km value was 275 ± 32 µM. The uptake was pH-dependent, being highest at pH 6.0, and was significantly decreased in the presence of PEPT1 inhibitors [glycylsarcosine (Gly-Sar), cephalexin, valaciclovir, glycylglycine, and glycylproline]. In metabolism assay using rat intestinal mucosa, rat hepatic microsomes, and human hepatocytes, the amount of Phe-Ψ-Ala was unchanged, whereas phenylalanylalanine was extensively decomposed. The clearance, distribution volume, and half-life of intravenously administered Phe-Ψ-Ala in rats were 0.151 ± 0.008 L/h/kg, 0.235 ± 0.012 L/kg, and 1.14 ± 0.07 h, respectively. The maximum plasma concentration of orally administered Phe-Ψ-Ala (2.31 ± 0.60 µg/mL) in the presence of Gly-Sar was significantly decreased compared with that in the absence of glycylsarcosine (3.74 ± 0.44 µg/mL), suggesting that the intestinal absorption of Phe-Ψ-Ala is mediated by intestinal PEPT1. In conclusion, our results indicate that Phe-Ψ-Ala is a high-affinity, metabolically stable, non-radioactive probe for PEPT1, and it should prove useful in studies of PEPT1, e.g., for predicting drug-drug interactions mediated by PEPT1 in vitro and in vivo.