Dynamic dialysis: an efficient technique for large-volume sample desalting.

Dialysis is a well-known technique for laboratory separation. However, its efficiency is commonly restricted by the dialyzer volume and its passive diffusion manner. In addition, the sample is likely to be precipitated and inactive during a long dialysis process. To overcome these drawbacks, a dynamic dialysis method was described and evaluated. The dynamic dialysis was performed by two peristaltic pumps working in reverse directions, in order to drive countercurrent parallel flow of sample and buffer, respectively. The efficiency and capacity of this dynamic dialysis method was evaluated by recording and statistically comparing the variation of conductance from retentate under different conditions. The dynamic method was proven to be effective in dialyzing a large-volume sample, and its efficiency changes proportionally to the flow rate of sample. To sum up, circulating the sample and the buffer creates the highest possible concentration gradient to significantly improve dialysis capacity and shorten dialysis time.

Food and bile micelle binding of zwitterionic antihistamine drugs.

Background and purpose: The food effects on oral drug absorption are challenging to predict from in vitro data. Food intake has been reported to reduce the oral absorption of several zwitterionic antihistamine drugs. However, the mechanism for this negative food effect has not been clear. The purpose of the present study was to evaluate the bile micelle and food binding of zwitterionic antihistamine drugs as a possible mechanism for the negative food effects on their oral drug absorption. Experimental approach: Bilastine (BIL), cetirizine (CET), fexofenadine (FEX), and olopatadine (OLO) were employed as model drugs. The fed/fasted AUC ratios of BIL, CET, FEX, and OLO after oral administration are reported to be 0.60 to 0.7, 0.92, 0.76 to 0.85, and 0.84, respectively. The unbound fraction (f u) of these drugs in the fasted and fed state simulated intestinal fluids (FaSSIF and FeSSIF, containing 3 and 15 mM taurocholic acid, respectively) with or without FDA breakfast homogenate (BFH) was measured by dynamic dialysis. Key results: The FeSSIF/ FaSSIF fu ratios were 0.90 (BIL), 0.46 (CET), 0.76 (FEX), and 0.78 (OLO). In the presence of BFH, the fu ratios were reduced to 0.52 (BIL), 0.22 (CET), 0.39 (FEX), and 0.44 (OLO). Conclusion: Despite being zwitterion at pH 6.5, the antihistamine drugs were bound to bile micelles. Bile micelle and food binding were suggested to cause a negative food effect on the oral absorption of these drugs. However, the AUC ratio was not quantitatively predicted by using FeSSIF + BFH.

Food and bile micelle binding of quaternary ammonium compounds.

Background and Purpose: Physiologically-based biopharmaceutics modeling (PBBM) has been widely used to predict the oral absorption of drugs. However, the prediction of food effects on oral drug absorption is still challenging, especially for negative food effects. Marked negative food effects have been reported in most cases of quaternary ammonium compounds (QAC). However, the mechanism has remained unclear. The purpose of the present study was to investigate the bile micelle and food binding of QACs as a mechanism of the negative food effect. Experimental Approach: Trospium (TRS), propantheline (PPT), and ambenonium (AMB) were selected as model QAC drugs. The oral absorption of these QACs has been reported to be reduced by 77% (TRS), > 66% (PPT), and 79% (AMB), when taken with food. The fasted and fed state simulated intestinal fluids (FaSSIF and FeSSIF, containing 3 and 15 mM taurocholic acid, respectively) with or without FDA breakfast homogenate (BFH) were used as the simulated intestinal fluid. The unbound fraction (fu) of the QACs in these media was measured by dynamic dialysis. Key Results: The fu ratios (FeSSIF/ FaSSIF) were 0.67 (TRS), 0.47 (PPT), and 0.76 (AMB). When BFH was added to FeSSIF, it was reduced to 0.39 (TRS), 0.28 (PPT), and 0.59 (AMB). Conclusion: These results suggested that bile micelle and food binding play an important role in the negative food effect on the oral absorption of QACs.

Mechanistic model and analysis of doxorubicin release from liposomal formulations.

Reliable and predictive models of drug release kinetics in vitro and in vivo are still lacking for liposomal formulations. Developing robust, predictive release models requires systematic, quantitative characterization of these complex drug delivery systems with respect to the physicochemical properties governing the driving force for release. These models must also incorporate changes in release due to the dissolution media and methods employed to monitor release. This paper demonstrates the successful development and application of a mathematical mechanistic model capable of predicting doxorubicin (DXR) release kinetics from liposomal formulations resembling the FDA-approved nanoformulation DOXIL® using dynamic dialysis. The model accounts for DXR equilibria (e.g. self-association, precipitation, ionization), the change in intravesicular pH due to ammonia release, and dialysis membrane transport of DXR. The model was tested using a Box-Behnken experimental design in which release conditions including extravesicular pH, ammonia concentration in the release medium, and the dilution of the formulation (i.e. suspension concentration) were varied. Mechanistic model predictions agreed with observed DXR release up to 19h. The predictions were similar to a computer fit of the release data using an empirical model often employed for analyzing data generated from this type of experimental design. Unlike the empirical model, the mechanistic model was also able to provide reasonable predictions of release outside the tested design space. These results illustrate the usefulness of mechanistic modeling to predict drug release from liposomal formulations in vitro and its potential for future development of in vitro - in vivo correlations for complex nanoformulations.

Mucoadhesivity and release properties of quaternary ammonium-chitosan conjugates and their nanoparticulate supramolecular aggregates: an NMR investigation.

Selective relaxation rate measurements effectively proved the affinity of dexamethasone 21-phosphate disodium salt for quaternary ammonium-chitosan conjugates, their thiolated derivatives and the corresponding nanostructured aggregates. Affinity was also probed by dynamic dialysis. The release profile of dexamethasone loaded nanoparticles was defined by quantitative NMR and interrupted dialysis experiments, and mucoadhesivity of empty nanoparticles was effectively probed by selective relaxation rate measurements.