Characterization of Substrates and Inhibitors for the In Vitro Assessment of Bcrp Mediated Drug–Drug Interactions

Purpose   In vitro assessment of drug candidates' affinity for multi-drug resistance proteins is of crucial importance for the prediction of in vivo pharmacokinetics and drug–drug interactions. To have well described experimental tools at hand, the objective of the study was to characterize substrates and inhibitors of Breast Cancer Resistance Protein (BCRP) and P-glycoprotein (P-gp). Methods  Madin–Darbin canine kidney cells overexpressing mouse Bcrp (MDCKII-Bcrp) were incubated with various Bcrp substrates, or a mixture of substrate and inhibitor to either the apical (A) or basolateral (B) compartment of insert filter plates. Substrate concentrations in both compartments at time points t = 0 h and t = 2 h were determined by LC–MS/MS, and respective permeation coefficients (P _app) and efflux ratios were calculated. Results  The Bcrp inhibitor Ko143 blocked topotecan and ABZSO transport in a concentration-dependent manner. P-gp inhibitors ivermectin, LY335979, PSC833, and the P-gp/Bcrp inhibitor ritonavir did not influence Bcrp mediated topotecan transport, however, blocked ABZSO transport. Additionally, neither was ABZSO transport influenced by topotecan, nor topotecan transport by ABZSO. Conclusions  Data suggest different modes of substrate and inhibitor binding to Bcrp. In order to not overlook potential drug–drug interactions when testing drug candidates for inhibitory potential towards Bcrp, distinct Bcrp probe substrates should be used.     

In Vitro and In Silico Strategies to Identify OATP1B1 Inhibitors and Predict Clinical Drug–Drug Interactions

Purpose  

To establish in vitro and in silico models that predict clinical drug–drug interactions (DDIs) with the OATP1B1 (SLCO1B1) transporter.     

Assessment of ABCG2-mediated transport of xenobiotics across the blood–milk barrier of dairy animals using a new MDCKII in vitro model

The ATP-binding cassette (ABC) efflux transporter ABCG2 represents the main route for active secretion of drugs and toxins across the blood–milk barrier, thereby producing a potential health risk for dairy consumers through formation of relevant residues in milk. However, no suitable in vitro model is as yet available to systematically investigate ABCG2-mediated transport of xenobiotics into milk of dairy animals. We recently cloned ABCG2 from the lactating mammary gland of dairy cows (bABCG2) and goats (cABCG2). Thus, the objective of this study was to generate a suitable blood–milk barrier in vitro model using polarized MDCKII monolayers stably expressing mammary bABCG2 or cABCG2. ABCG2 protein was localized by confocal microscopy to the apical and lateral plasma membrane of polarized MDCKII cells. Intact barrier function of MDCKII-bABCG2 and MDCKII-cABCG2 monolayers was confirmed by determination of cell permeability of transcellular marker propranolol and paracellular marker atenolol which was ≤1 %. In flux assays, ABCG2 substrate 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) showed preferential basolateral to apical (B > A) transport in ABCG2-MDCKII cells. This apically directed PhIP transport was significantly inhibited by ABCG2 inhibitor fumitremorgin C (FTC) or the flavonoid equol. PhIP B > A transport in MDCKII-bABCG2 monolayers was additionally decreased by ABCG2 inhibitor Ko143. The fluoroquinolone antibiotic enrofloxacin was identified as a substrate of ruminant mammary ABCG2. The analgesic drug sodium salicylate was shown to be substrate of bABCG2 but not of cABCG2. Thus, the generated mammary ABCG2-expressing MDCKII cells represent a valuable tool to study active secretion of drugs and toxins into milk.     

Characterization of an In Vitro Blood–Brain Barrier Model System for Studying Drug Transport and Metabolism

Bovine brain micro vessel endothelial cells have been isolated and grown in culture to monolayers. These endothelial cell monolayers have been characterized morphologically with electron microscopy, histochemically for brain endothelium enzyme markers, alkaline phosphatase and -glutamyl trans-peptidase, and by immunofluorescence to detect Factor VIII antigen, an exclusive endothelial antigen. Results of these studies indicate that the cells forming the monolayers are of endothelial origin and possess many features of the in vivo brain endothelium responsible for formation of the blood–brain barrier. This in vitro blood–brain barrier model system was used in experiments to determine the permeability of the cultured monolayer to sucrose, leucine, and propranolol. Leucine rapidly moved across the monolayers of this in vitro system and tended to plateau after approximately 10 min. In contrast, the rates of sucrose and propranolol movement were linear during a 1-hr observation period, with the rate of propranolol movement across the monolayer greater than that of sucrose. The ability to detect differences in the permeability of the monolayers to leucine, propranolol, and sucrose with radioactive tracers suggests that this in vitro model system will be an important tool for the investigation of the role of the blood–brain barrier in the delivery of centrally acting drugs and nutrients.     

An In Silico Transwell Device for the Study of Drug Transport and Drug–Drug Interactions

PURPOSE: Validate and exemplify a discrete, componentized, in silico, transwell device (ISTD) capable of mimicking the in vitro passive transport properties of compounds through cell monolayers. Verify its use for studying drug-drug interactions. METHODS: We used the synthetic modeling method. Specialized software components represented spatial and functional features including cell components, semi-porous tight junctions, and metabolizing enzymes. Mobile components represented drugs. Experiments were conducted and analyzed as done in vitro. RESULTS: Verification experiments provided data analogous to those in the literature. ISTD parameters were tuned to simulate and match in vitro urea transport data; the objects representing tight junction (effective radius of 6.66 A) occupied 0.066% of the surface area. That ISTD was then tuned to simulate pH-dependent, in vitro alfentanil transport properties. The resulting ISTD predicted the passive transport properties of 14 additional compounds, individually and all together in one in silico experiment. The function of a two-site enzymatic component was cross-validated with a kinetic model and then experimentally validated against in vitro benzyloxyresorufin metabolism data. Those components were used to exemplify drug-drug interaction studies. CONCLUSIONS: The ISTD is an example of a new class of simulation models capable of realistically representing complex drug transport and drug-drug interaction phenomena.     

Drug–Drug Interaction Potential of Marketed Oncology Drugs: In Vitro Assessment of Time-Dependent Cytochrome P450 Inhibition, Reactive Metabolite Formation and Drug–Drug Interaction Prediction

Purpose

To evaluate 26 marketed oncology drugs for time-dependent inhibition (TDI) of cytochrome P450 (CYP) enzymes. Evaluate TDI-positive drugs for potential to generate reactive intermediates. Assess clinical drug–drug interaction (DDI) risk using static mechanistic models.

Methods

Human liver microsomes and CYP-specific probes were used to assess TDI in a dilution shift assay followed by generation of K_I and k_inact. Reactive metabolite trapping studies were performed with stable label probes. Static mechanistic model was used to predict DDI risk using a 1.25-fold AUC increase as a cut-off for positive DDI.

Results

Negative TDI across CYPs was observed for 13/26 drugs; the rest were time-dependent inhibitors of, predominantly, CYP3A. The k_inact/K_I ratios for 11 kinase inhibitors ranged from 0.7 to 42.2 ml/min/μmol. Stable label trapping agent–drug conjugates were observed for ten kinase inhibitors. DDI predictions gave no false negatives, one true negative, four false positives and three true positives. The magnitude of DDI was overestimated irrespective of the inhibitor concentration selected.

Conclusions

13/26 oncology drugs investigated showed TDI potential towards CYP3A, formation of reactive metabolites was also observed. An industry standard static mechanistic model gave no false negative predictions but did not capture the modest clinical DDI potential of kinase inhibitors.     

Synthesis of a New pH-Sensitive Folate–Doxorubicin Conjugate and its Antitumor Activity In Vitro

Folate–aminocaproic acid–doxorubicin (FA–AMA–DOX) was synthesized and characterized by H NMR spectroscopy and mass spectrometry. Cytotoxicity and cellular uptake experiments were performed in KB and HepG2 cells, which express folic acid receptor, and the cell line A549, which does not express folic acid receptor. Cytotoxicity was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and cellular uptake was monitored using fluorescence microscopy. The amount of DOX released from FA–AMA–DOX was much greater at pH 5.0 than that at pH 6.5 or 7.4. The cytotoxicity of FA–AMA–DOX toward KB and HepG2 cells was greater than that of DOX or AMA–DOX at the same concentrations, and cytotoxicity could be attenuated by FA in a dose-dependent manner. On the contrary, the cytotoxicity of FA–AMA–DOX and AMA–DOX toward A549 cells was lower than that of DOX at the same concentration, and cytotoxicity could not be reduced by FA. Compared with FA–AMA, FA–AMA–DOX increased the intracellular accumulation of DOX in KB cells. These results suggested that FA–AMA–DOX have suitable attributes for the active targeting of folate-receptor-positive tumor cells and for releasing the chemotherapeutic agent, DOX, in situ; it therefore has potential as a novel cancer therapeutic. © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 102:530–540, 2013     

Determination of Atypical Nonlinear Plasma–Protein-Binding Behavior of Tigecycline Using an In Vitro Microdialysis Technique

Tigecycline, a novel glycylcycline antibiotic, shows atypical nonlinear plasma–protein-binding behavior using ultrafiltration and ultracentrifugation techniques. The mechanism of such counterintuitive behavior is currently unknown. Ultrafiltration and ultracentrifugation cause fractional change in protein concentration and therefore may influence plasma–protein binding. Microdialysis (MD), a novel technique, can sample unbound drugs without any change in fractional protein concentration. To determine whether the atypical nonlinear plasma–protein-binding behavior is not related to measurement technique, the plasma–protein binding of tigecycline was determined using MD. A sensitive liquid chromatography-mass spectrometry method was developed and validated for the bioanalysis of tigecycline in the dialysate. The probe recoveries and plasma–protein binding of tigecycline at four different concentration levels 0.1, 1, 10, and 100 μg/mL were determined. Similar to ultracentrifugation and ultrafiltration, MD also showed atypical nonlinear plasma–protein-binding behavior of tigecycline up to 10 μg/mL, but unbound fraction increased at 100 μg/mL indicating saturation of mechanism responsible for atypical nonlinear behavior. This study concludes that the atypical nonlinear binding behavior of tigecycline is not technique-dependent, rather it is a true behavior of tigecycline. Further investigations are necessary to elucidate the mechanism.     

Applications of In Vitro–In Vivo Correlations in Generic Drug Development: Case Studies

In vitro–in vivo correlation (IVIVC) is a predictive mathematical model describing the relationship between an in vitro property and a relevant in vivo response. The main objective of an IVIVC is to serve as a surrogate for human bioequivalence (BE) studies, which may reduce the number of BE studies performed during the initial approval process as well as with certain scale-up and postapproval changes. The US Food and Drug Administration (FDA) published a regulatory guidance related to development, evaluation, and applications of IVIVC for extended-release (ER) oral dosage forms in September 1997. Despite the publication of this guidance, the deficiencies related to IVIVC are still identified by the Division of Bioequivalence in the process of Abbreviated New Drug Application (ANDA) review. Thus, the main objective of this article is to present the most commonly occurring deficiencies associated with IVIVCs via selected case studies from the ANDAs for oral ER drug products only. We searched internal FDA databases from January 1996 to December 2014 to identify the ANDAs for proposed generic oral ER drug products containing IVIVC. Only 14 ANDA submissions had IVIVC data, and most were not acceptable. Only one ANDA submission included adequate information related to IVIVC data enabling the completion of BE review within first review cycle. It is hoped that awareness of the deficiencies presented in our article would help the generic drug applicants to submit complete and appropriate information related to IVIVC data, ultimately, resulting in a more timely approval of ANDAs.KEY WORDS: bioequivalence, extended-release drug products, generics, IVIVC, SUPAC     

Assessment of Drug–drug Interaction and Optimization in Capecitabine and Irinotecan Combination Regimen using a Physiologically Based Pharmacokinetic Model

Capecitabine and irinotecan (CPT-11) combination regimen (XELIRI) is used for colorectal cancer treatment. Capecitabine is metabolized to 5-fluorouracil (5-FU) by three enzymes, including carboxylesterase (CES). CES can also convert CPT-11 to 7-ethyl-10-hydroxycamptotecin (SN-38). CES is involved in the metabolic activation of both capecitabine and CPT-11, and it is possible that drug–drug interactions occur in XELIRI. Here, a physiologically based pharmacokinetic (PBPK) model was developed to evaluate drug–drug interactions. Capecitabine (180 mg/kg) and CPT-11 (180 mg/m²) were administered to rats, and blood (250 μL) was collected from the jugular vein nine times after administration. Metabolic enzyme activities and K_i values were calculated through in vitro experiments. The plasma concentration of 5-FU in XELIRI was significantly decreased compared to capecitabine monotherapy, and metabolism of capecitabine by CES was inhibited by CPT-11. A PBPK model was developed based on the in vivo and in vitro results. Furthermore, a PBPK model-based simulation was performed with the capecitabin dose ranging from 0 to 1000mol/kg in XELIRI, and it was found that an approximately 1.7-fold dosage of capecitabine was required in XELIRI for comparable 5-FU exposure with capecitabine monotherapy. PBPK model-based simulation will contribute to the optimization of colorectal cancer chemotherapy using XELIRI.     

In Vitro Evaluation of Reversible and Irreversible Cytochrome P450 Inhibition: Current Status on Methodologies and their Utility for Predicting Drug–Drug Interactions

It is widely accepted that today's practice of polypharmacy inevitably increases the incidence of drug-drug interactions (DDIs). Serious DDI is a major liability for any new chemical entity (NCE) entering the pharmaceutical market. As such, pharmaceutical companies employ various strategies to avoid problematic compounds for clinical development. A key cause for DDIs is the inhibition of cytochrome P450 enzymes (CYPs) that are responsible for metabolic clearance of many drugs. Screening for inhibition potency of CYPs by NCEs has therefore become a routine practice during the drug discovery stage. However, in order to make proper use of DDI data, an understanding of the strengths and weaknesses of the various experimental systems in current use is required. An illustrated review of experimental practices is presented with discussion of likely future developments. The combination of high quality in vitro data generation and the application of in vivo CYP inhibition modelling approaches should allow more informed decisions to be made in the search for drug molecules with acceptable DDI characteristics.     

Pharmacokinetic Parameters Determination and In Vitro–In Vivo Correlation of Ileocolonic-Targeted pH-Responsive Coated Mini-Tablets of Naproxen

This research work aims to determine the pharmacokinetic parameters and in vitro-in vivo correlation of the selected ileocolonic-targeted coated mini-tablet filled capsule formulation of naproxen. The pure suspension and coated mini-tablet filled capsule formulation of naproxen were administered to adult albino rabbits through the oral route. The samples were analyzed for naproxen by an HPLC method. For the pure drug suspension, the peak plasma concentration was found as 8.499±0.029 μg/ml at 1.139±0.010 hours and the half-life was found to be 9.459±0.387 hours, whereas for the formulation the peak plasma concentration was found as 6.814±0.037 μg/ml at 8.042±0.069 hours and the half-life was found to be 19.657±0.359 hours. This decreased the peak plasma concentration at a delayed time and increased the half-life of the capsule formulation in comparison with the pure drug suspension which showed that naproxen was only targeted to the ileocolonic region. A significant in vitro-in vivo correlation (i.e. R²=0.9901) was also obtained. Thus, the results of these findings suggest that naproxen formulated as coated mini-tablets can be suitable for targeted ileocolonic drug delivery.     

A Biopredictive In Vitro Comparison of Oral Locally Acting Mesalazine Formulations by a Novel Dissolution Model for Assessing Intraluminal Drug Release in Individual Subjects

Drug release and availability at the site of action are the major factors determining the clinical response for locally-acting gastrointestinal (GI) drug products. The present work focused on the prediction of site and extent of in vivo mesalazine release after oral administration to a variety of subjects using individualized in vitro drug release experiments. First, experiments mimicking GI passages in average adult subjects were performed. Then, results from a study screening fasted in vivo pH and transit profiles in individual subjects were translated into a novel in vitro dissolution model enabling to mimic individual GI pH-profiles and transit times with physiologically relevant dissolution media. A selection of monolithic and multiparticulate mesalazine formulations with pH-dependent and pH-independent drug release was screened with the novel dissolution model. Results of the study indicate that dosage form performance can be significantly different in individual subjects and highlight the importance of addressing individual physiological parameters relevant to intraluminal drug release when the aim is to predict the in vivo performance of locally-acting mesalazine formulations in individual patients. The novel in vitro dissolution approach thus represents a valuable tool for both improving individual oral therapy with locally-acting GI drug products and assessing bioequivalence of these formulations.     

Assessment of the Protein–Protein Interactions in a Highly Concentrated Antibody Solution by Using Raman Spectroscopy

Purpose

To investigate the protein–protein interactions of a highly concentrated antibody solution that could cause oligomerization or aggregation and to develop a better understanding of the optimization of drug formulations.

Methods

In this study, we used Raman spectroscopy to investigate the structure and interactions of a highly concentrated antibody solution over a wide range of concentrations (10–200 mg/mL) with the aid of a multivariate analysis.

Results

Our analysis of the amide I band, I ₈₅₆ /I ₈₃₀ of Tyr, and the relative intensity at 1004 cm^?1 of the Phe and OH stretching region at around 3000 cm^?1 showed that across this wide range of concentrations, the secondary structure of the IgG molecules did not change; however, short-range attractive interactions around the Tyr and Phe residues occurred as the distance between the IgG molecules decreased with increasing concentration. Analysis of the OH stretching region at around 3000 cm^?1 showed that these short-range attractive interactions correlated with the amount of hydrated water around the IgG molecules.

Conclusions

Our data show that Raman spectroscopy can provide valuable information of the protein–protein interactions based on conformational approaches to support conventional colloidal approaches, especially for analyses of highly concentrated solutions.

     

Evaluation of Drug Combination Effect Using a Bliss Independence Dose–Response Surface Model

To test the anticancer effect of combining two drugs targeting different biological pathways, the popular way to show synergistic effect of drug combination is a heat map or surface plot based on the percent excess the Bliss prediction using the average response measures at each combination dose. Such graphs, however, are inefficient in the drug screening process and it does not give a statistical inference on synergistic effect. To make a statistically rigorous and robust conclusion for drug combination effect, we present a two-stage Bliss independence response surface model to estimate an overall interaction index (τ) with 95% confidence interval (CI). By taking into all data points account, the overall τ with 95% CI can be applied to determine if the drug combination effect is synergistic overall. Using some example data, the two-stage model was compared to a couple of classic models following Bliss rule. The data analysis results obtained from our model reflect the pattern shown from other models. The application of overall τ helps investigators to make decision easier and accelerate the preclinical drug screening.     

Influence of Drug Property and Product Design on In Vitro–In Vivo Correlation of Complex Modified-Release Dosage Forms

The present study examines how drug's inherent properties and product design influence the evaluation and applications of in vitro–in vivo correlation (IVIVC) for modified-release (MR) dosage forms consisting of extended-release (ER) and immediate-release (IR) components with bimodal drug release. Three analgesic drugs were used as model compounds, and simulations of in vivo pharmacokinetic profiles were conducted using different release rates of the ER component and various IR percentages. Plasma concentration–time profiles exhibiting a wide range of t_max and maximum observed plasma concentration (C_max) were obtained from superposition of the simulated IR and ER profiles based on a linear IVIVC. It was found that depending on the drug and dosage form design, direct use of the superposed IR and ER data for IVIVC modeling and prediction may (1) be acceptable within errors, (2) become unreliable and less meaningful because of the confounding effect from the non-negligible IR contribution to C_max, or (3) be meaningless because of the insensitivity of C_max to release rate change of the ER component. Therefore, understanding the drug, design and drug release characteristics of the product is essential for assessing the validity, accuracy, and reliability of IVIVC of complex MR products obtained via directly modeling of in vivo data.     

Predictions of In Vivo Prolactin Levels from In Vitro K i Values of D2 Receptor Antagonists Using an Agonist–Antagonist Interaction Model

Prolactin elevation is a side effect of all currently available D₂ receptor antagonists used in the treatment of schizophrenia. Prolactin elevation is the result of a direct antagonistic D₂ effect blocking the tonic inhibition of prolactin release by dopamine. The aims of this work were to assess the correlation between in vitro estimates of D₂ receptor affinity and pharmacokinetic–pharmacodynamic model-based estimates obtained from analysis of clinical data using an agonist–antagonist interaction (AAI) model and to assess the value of such a correlation in early prediction of full prolactin time profiles. A population model describing longitudinal prolactin data was fitted to clinical data from 16 clinical phases 1 and 3 trials including five different compounds. Pharmacokinetic data were modeled for each compound and the prolactin model was both fitted in per-compound fits as well as simultaneously to all prolactin data. Estimates of prolactin elevating potency were compared to corresponding in vitro values and their predictability was evaluated through model-based simulations. The model successfully described the prolactin time course for all compounds. Estimates derived from experimental preclinical data and the model fit of the clinical data were strongly correlated (p < 0.001), and simulations adequately predicted the prolactin elevation in five out of six compounds. The AAI model has the potential to be used in drug development to predict prolactin response for a given exposure of D₂ antagonists using routinely produced preclinical data.Key words: in vitro–in vivo correlation, pharmacodynamic scaling, population modeling, prolactin     

Integrated Population Pharmacokinetic Model of Both Cyclophosphamide and Thiotepa Suggesting a Mutual Drug–Drug Interaction

PURPOSE/AIMS: Cyclophosphamide (CP) and thiotepa (TT) are frequently administered simultaneously in high-dose chemotherapy regimens. The prodrug CP shows strong autoinduction resulting in increased formation of its activated metabolite 4-hydroxycyclophosphamide (4OHCP). TT inhibits this bioactivation of CP. Previously, we successfully modelled CP bioactivation and the effect of TT on the autoinduction. Recently we suggested that CP may also induce the conversion of TT in to its metabolite tepa (T). The aim of the current study was to investigate whether the influence of CP on TT metabolism can be described with a population pharmacokinetic model and whether this interaction can be incorporated in an integrated model describing both CP and TT pharmacokinetics. METHODS: Plasma samples were collected from 49 patients receiving 86 courses of a combination of high-dose CP (4000 or 6000 mg/m2), TT (320 or 480 mg/m2) and carboplatin (1067 or 1600 mg/m2) given in short infusions during four consecutive days. For each patient, approximately 20 plasma samples were available per course. Concentrations of CP, 4OHCP, TT and T were determined using GC and HPLC. Kinetic data were processed using NONMEM. RESULTS: The pharmacokinetics of TT and T were described with a two-compartment model. TT was eliminated through a non-inducible and an inducible pathway, the latter resulting information of T (ClindTT = 12.4 l/hr, ClnonindTT = 17.0 l/hr). Induction of TT metabolism was mediated by a hypothetical amount of enzyme, different from that involved in CP induction, whose amount increased with time in the presence of CP. The amount of enzyme followed a zero-order formation and a decrease with a first-order elimination rate constant of 0.0343 hr(-1) (t1/2 = 20 hr). This model was significantly better than a model lacking the induction by CP. The model was successfully incorporated into the previously published pharmacokinetic model for CP, and resulted in comparable parameter estimates for this compound and its metabolite 4OHCP. CONCLUSION: The pharmacokinetics of TT, when administered in combination with CP, were successfully described. The model confirms induction of TT metabolism with time and it appears likely that CP is responsible for this phenomenon. The existence of a mutual pharmacokinetic interaction between CP and TT, as described in our integrated model, may be relevant in clinical practice.     

Quantitative Prediction of Oral Bioavailability of a Lipophilic Antineoplastic Drug Bexarotene Administered in Lipidic Formulation Using a Combined In Vitro Lipolysis/Microsomal Metabolism Approach

For performance assessment of the lipid-based drug delivery systems (LBDDSs), in vitro lipolysis is commonly applied because traditional dissolution tests do not reflect the complicated in vivo micellar formation and solubilization processes. Much of previous research on in vitro lipolysis has mostly focused on rank-ordering formulations for their predicted performances. In this study, we have incorporated in vitro lipolysis with microsomal stability to quantitatively predict the oral bioavailability of a lipophilic antineoplastic drug bexarotene (BEX) administered in LBDDS. Two types of LBDDS were applied: lipid solution and lipid suspension. The predicted oral bioavailability values of BEX from linking in vitro lipolysis with microsomal stability for lipid solution and lipid suspension were 34.2 ± 1.6% and 36.2 ± 2.6%, respectively, whereas the in vivo oral bioavailability of BEX was tested as 31.5 ± 13.4% and 31.4 ± 5.2%, respectively. The predicted oral bioavailability corresponded well with the oral bioavailability for both formulations, demonstrating that the combination of in vitro lipolysis and microsomal stability can quantitatively predict oral bioavailability of BEX. In vivo intestinal lymphatic uptake was also assessed for the formulations and resulted in <1% of the dose, which confirmed that liver microsomal stability was necessary for correct prediction of the bioavailability.     

An In Vitro and In Vivo Comparison of Solid and Liquid–Oil Cores in Transdermal Aconitine Nanocarriers

This study compared transdermal aconitine delivery using solid lipid nanoparticles (SLN) and microemulsion (ME) vehicles. Aconitine‐loaded SLN and ME were formulated with the same surfactant, cosurfactant, and water content, with an equal amount of oil matrix (ATO 888 for SLN and ethyl oleate for ME). These nanosized formulations (70–90 nm) showed suitable pH values and satisfactory skin tissue biocompatibility. SLN contained a higher concentration of smaller nanoparticles, compared with that in ME. Neither of the nanocarriers penetrated across excised skin in their intact form. In vitro transdermal delivery studies found that transdermal aconitine flux was lower from SLN than from ME (p < 0.05), but skin aconitine deposition was higher using SLN (p < 0.05). Fluorescence‐activated cell sorting indicated that in vitro uptake of fluorescently labeled SLN by human immortalized keratinocyte (HaCaT) cells was greater than that of ME, indicating that a transcellular pathway may contribute to cutaneous drug absorption more effectively from SLN. In vivo studies found that these formulations could loosen stratum corneum layers and increase skin surface crannies, which may also enhance transdermal aconitine delivery. SLN produced a more sustained aconitine release, indicating that compared with ME, this transdermal delivery vehicle may reduce the toxicity of this drug. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:3602–3610, 2014