The potential of microdialysis to estimate rifampicin concentrations in the lung of guinea pigs

Pharmacokinetics of tilmicosin in chicken joints based on a novel microdialysis sampling method

Microdialysis is a continuous direct sampling technique used in live animals to study pharmacokinetic (PK) characteristics of drugs directly in target organs. The antibiotic tilmicosin used to treat arthritis in chickens caused by Mycoplasma synoviae. However, the PK study of tilmicosin in chicken joint has not been reported. The aim of this study was to explore the PK characteristics and penetration of tilmicosin by microdialysis incorporated with High-Performance Liquid Chromatography Mass Spectrometry (HPLC-MS/MS). An articular cavity microdialysis sampling model was established by determining in vivo and in vitro recovery results. Tilmicosin was orally administered to chickens and flow rate testing combined with retro-dialysis were used to determine tilmicosin concentration in the target synovial space. HPLC-MS/MS quantification of tilmicosin from plasma and joint dialysate indicated that recovery was negatively correlated with flow rate and the optimal perfusion rate was determined to be 1.0 μL/min. The AUC, C_max , MRT and t_1/2 in plasma were 4.6, 3.0, 2.2 and 1.6 times higher than in the joint dialysate, respectively, but T_max did not significantly differ. The penetration of tilmicosin from plasma to joint (AUC_dialysate /AUC_plasma ) was 0.24 and indicated tilmicosin concentration in joints was much lower than that of plasma. Microdialysis technology provides a novel technique to study pharmacokinetics directly in target tissues and our study provides a reference for the clinical use of tilmicosin for treatment of M. synoviae infections in articular cavities.

Effect of CYP3A4 Inhibitors and Inducers on Pharmacokinetics and Pharmacodynamics of Saxagliptin and Active Metabolite M2 in Humans Using Physiological-Based Pharmacokinetic Combined DPP-4 Occupancy

We aimed to develop a physiological-based pharmacokinetic and dipepidyl peptidase 4 (DPP-4) occupancy model (PBPK-DO) characterized by two simultaneous simulations to predict pharmacokinetic (PK) and pharmacodynamic changes of saxagliptin and metabolite M2 in humans when coadministered with CYP3A4 inhibitors or inducers. Ketoconazole, delavirdine, and rifampicin were selected as a CYP3A4 competitive inhibitor, a time-dependent inhibitor, and an inducer, respectively. Here, we have successfully simulated PK profiles and DPP-4 occupancy profiles of saxagliptin in humans using the PBPK-DO model. Additionally, under the circumstance of actually measured values, predicted results were good and in line with observations, and all fold errors were below 2. The prediction results demonstrated that the oral dose of saxagliptin should be reduced to 2.5 mg when coadministrated with ketoconazole. The predictions also showed that although PK profiles of saxagliptin showed significant changes with delavirdine (AUC 1.5-fold increase) or rifampicin (AUC: a decrease to 0.19-fold) compared to those without inhibitors or inducers, occupancies of DPP-4 by saxagliptin were nearly unchanged, that is, the administration dose of saxagliptin need not adjust when there is coadministration with delavirdine or rifampicin.