Intestinal Permeability of ß-Lapachone and Its Cyclodextrin Complexes and Physical Mixtures.

BACKGROUND AND OBJECTIVES: ß-Lapachone (ßLAP) is a promising, poorly soluble, antitumoral drug. ßLAP combination with cyclodextrins (CDs) improves its solubility and dissolution but there is not enough information about the impact of cyclodextrins on ßLAP intestinal permeability. The objectives of this work were to characterize ßLAP intestinal permeability and to elucidate cyclodextrins effect on the dissolution properties and on the intestinal permeability. The final goal was to evaluate CDs influence on the oral absorption of ßLAP. METHODS: Binary systems (physical mixtures and inclusion complexes) including ßLAP and CDs (ß-cyclodextrin: ßCD, random-methyl-ß-cyclodextrin: RMßCD and sulfobutylether-ß-cyclodextrin: SBEßCD) have been prepared and analysed by differential scanning calorimetry. ßLAP (and its combinations with CDs) absorption rate coefficients and effective permeability values have been determined in vitro in MDCK or MDCK-Mdr1 monolayers and in situ in rat by a closed loop perfusion technique. RESULTS: DSC results confirmed the formation of the inclusion complexes. ßLAP-CDs inclusion complexes improve drug solubility and dissolution rate in comparison with physical mixtures. ßLAP presented a high permeability value which can provide complete oral absorption. Its oral absorption is limited by its low solubility and dissolution rate. Cyclodextrin (both as physical mixtures and inclusion complexes) showed a positive effect on the intestinal permeability of ßLAP. Complexation with CDs does not reduce ßLAP intestinal permeability in spite of the potential negative effect of the reduction in free fraction of the drug. CONCLUSIONS: The use of RMßCD or SBEßCD inclusion complexes could benefit ßLAP oral absorption by enhancing its solubility, dissolution rate and permeability.

Variability of permeability estimation from different protocols of subculture and transport experiments in cell monolayers.

INTRODUCTION: In vitro models with high predictive ability have been revealed as strong tools for pharmaceutical industry. However, the variability in permeability estimations complicates the comparison and combination of data from different laboratories and it makes necessary the careful validation of the model and the continuous suitability demonstration. The adequate standardization of pre-experimental, experimental and post-experimental factors might help to reduce the inter- and intra-laboratory variability in permeability values. METHODS: The objective of this paper is the evaluation of the effect of passage number, experimental protocol, time after seeding and calculation method on the permeability values and their variability in transport experiments in Caco-2, MDCK and MDCK-MDR1 cells. Metoprolol, Lucifer yellow and Rhodamine-123 were used to check the performance of the cell lines. Protocols used differ mainly in the differentiation time and the filter support coating with collagen. Data was analyzed with sink and non-sink approaches. The final purpose was to explore pre-experimental, experimental and post-experimental conditions in order to select the best experimental scenarios for permeability assays. RESULTS: Results indicated that for passive diffusion studies, coating helps cell differentiation in a more stable manner in all cell lines compared to protocol without coating which showed permeability changes with passages and more variable values. In both protocols the paracellular route became more restricted with higher passage numbers. Functionality of P-gp assessed with Rhodamine permeability did not change with passage number in Caco-2 cells with any of the protocols but increased in both protocols in MDCK and MDCK-MDR1 cells. Protocol without coating showed the less variable results in these cell lines. Rhodamine permeabilities increased with higher maturation times due to a higher expression of the transporter. Nevertheless for compounds absorbed by passive diffusion there was not a clear trend neither in permeability values nor in variability. DISCUSSION: As a conclusion, we have confirmed the influence of maturation conditions and passage number in permeability values and in their variability. Based on our results protocol with coating would be more adequate for studies of compounds absorbed by passive diffusion but the protocol without coating gave us better results for studies about P-gp interactions.

Permutation Test (PT) and Tolerated Difference Test (TDT): two new, robust and powerful nonparametric tests for statistical comparison of dissolution profiles.

The most popular way of comparing oral solid forms of drug formulations from different batches or manufacturers is through dissolution profile comparison. Usually, a similarity factor known as (f2) is employed; However, the level of confidence associated with this method is uncertain and its statistical power is low. In addition, f2 lacks the flexibility needed to perform in special scenarios. In this study two new statistical tests based on nonparametrical Permutation Test theory are described, the Permutation Test (PT), which is very restrictive to confer similarity, and the Tolerated Difference Test (TDT), which has flexible restrictedness to confer similarity, are described and compared to f2. The statistical power and robustness of the tests were analyzed by simulation using the Higuchi, Korsmayer, Peppas and Weibull dissolution models. Several batches of oral solid forms were simulated while varying the velocity of dissolution (from 30 min to 300 min to dissolve 85% of the total content) and the variability within each batch (CV 2-30%). For levels of variability below 10% the new tests exhibited better statistical power than f2 and equal or better robustness than f2. TDT can also be modified to distinguish different levels of similarity and can be employed to obtain customized comparisons for specific drugs. In conclusion, two new methods, more versatile and with a stronger statistical basis than f2, are described and proposed as viable alternatives to that method. Additionally, an optimized time sampling strategy and an experimental design-driven strategy for performing dissolution profile comparisons are described.

A new mathematical approach for the estimation of the AUC and its variability under different experimental designs in preclinical studies.

The aim of the present work was to develop a new mathematical method for estimating the area under the curve (AUC) and its variability that could be applied in different preclinical experimental designs and amenable to be implemented in standard calculation worksheets. In order to assess the usefulness of the new approach, different experimental scenarios were studied and the results were compared with those obtained with commonly used software: WinNonlin® and Phoenix WinNonlin®. The results do not show statistical differences among the AUC values obtained by both procedures, but the new method appears to be a better estimator of the AUC standard error, measured as the coverage of 95% confidence interval. In this way, the new proposed method demonstrates to be as useful as WinNonlin® software when it was applicable.