Photochemical Mechanism of Riboflavin-Induced Degradation of Famotidine and a Suggested Pharmaceutical Strategy for Improving Photostability.

The present study aimed to clarify the mechanism of photodegradation of famotidine with riboflavin (FMT/RF), and to develop a photochemically stabilized formulation of FMT/RF. Photochemical properties of RF were characterized by UV-VIS spectral analysis, reactive oxygen species (ROS) assay, and photostability testing. Pharmacokinetic study was conducted in rats after intravenous administration of FMT (1 mg/kg) formulation containing RF (0.01 mg/kg). The UV-VIS spectral pattern of RF partly overlapped with the sunlight spectrum, and ROS generation from photoirradiated RF was remarkable; thus, RF had high photoreactive potential. In the photostability testing, after irradiation (250 W/m(2)), degradation rate for FMT in FMT/RF was ca. 11-fold higher than that in FMT alone. The addition of radical scavengers to FMT/RF led to attenuated photodegradation of FMT/RF; in particular, the addition of L-ascorbic acid (vitamin C; VC) to FMT/RF showed ca. 86% inhibition of the photodegradation of FMT/RF. The pharmacokinetic study on FMT indicated that the addition of VC (1 mg/kg) to FMT/RF had no significant impact on the pharmacokinetic behavior of FMT. These findings suggest that ROS-mediated photochemical reaction would be involved in the photodegradation pathway of FMT/RF, and the complementary use of VC might be an attractive approach to improve the photostability of FMT/RF.

[Specific variability of teicoplanin protein binding in patients receiving continuous hemodiafiltration-comparison with hypoalbuminemia patients].

Variation in protein binding ratio (PBR) of teicoplanin (TEIC) was investigated in continuous hemodiafiltration (CHDF) patients. TEIC is classified as a high PBR drug (≧90%), and it was reported that the PBR of TEIC decreased with an decrease in the serum albumin level in hypoalbuminemia patients. However, few reports can be found about the variation of PBR of TEIC for CHDF patient. An antibiotic activity is directly determined by the level of unbound antibiotics species (Cfree) in the target site, namely, an increase in the Cfree enhances the risks of TEIC as well as the therapeutic effect against Methicillin-resistant Staphylococcus aureus (MRSA). In this study, both the total concentration (Ctotal) and Cfree of TEIC were determined and the PBRs were compared between a patient with normal albumin level, hypoalbuminemia patients and CHDF patients. Similarly to the previous report, the lowering of PBR of TEIC was demonstrated in the hypoalbuminemia patients. On the other hand, the CHDF patients showed lower value of PBR suggesting some change in the protein binding ability, although showed higher values of serum albumin level in comparison with the hypoalbuminemia patients. It was not necessary to measure the Cfree value for the hypoalbuminemia patient routinely, but the monitoring of Cfree as well as Ctotal for the CHDF patients can be important for the proper TEIC use because of the potential specialty of PBR.