The Biopharmaceutics Classification System: subclasses for in vivo predictive dissolution (IPD) methodology and IVIVC

Overview of Transporters in Pharmacokinetics and Drug Discovery

Transporters play important roles in absorption, distribution, metabolism, and elimination (ADME) processes, as well as drug pharmacokinetics (PK) and pharmacodynamics (PD). They are also important in maintaining the homeostasis of endogenous compounds and nutrients in the body. Increasing evidences also suggest that they are important in mediating drug-drug interactions (DDIs). While the significance of transporters in drug pharmacodynamics and DDIs are beyond the scope of this overview, the basic concepts of transporters, their contributions in membrane permeation processes, and their roles in influencing drug ADME pathway and PK will be discussed. © 2018 by John Wiley & Sons, Inc.

Evaluation and optimized selection of supersaturating drug delivery systems of posaconazole (BCS class 2b) in the gastrointestinal simulator (GIS): An in vitro-in silico-in vivo approach

Supersaturating drug delivery systems (SDDS) have been put forward in the recent decades in order to circumvent the issue of low aqueous solubility. Prior to the start of clinical trials, these enabling formulations should be adequately explored in in vitro/in silico studies in order to understand their in vivo performance and to select the most appropriate and effective formulation in terms of oral bioavailability and therapeutic outcome. The purpose of this work was to evaluate the in vivo performance of four different oral formulations of posaconazole (categorized as a biopharmaceutics classification system (BCS) class 2b compound) based on the in vitro concentrations in the gastrointestinal simulator (GIS), coupled with an in silico pharmacokinetic model to predict their systemic profiles. Recently published intraluminal and systemic concentrations of posaconazole for these formulations served as a reference to validate the in vitro and in silico results. Additionally, the morphology of the formed precipitate of posaconazole was visualized and characterized by optical microscopy studies and thermal analysis. This multidisciplinary work demonstrates an in vitro-in silico-in vivo approach that provides a scientific basis for screening SDDS by a user-friendly formulation predictive dissolution (fPD) device in order to rank these formulations towards their in vivo performance.

pH-permeability profiles for drug substances: Experimental detection, comparison with human intestinal absorption and modelling

The influence of pH on human intestinal absorption is frequently not considered in early drug discovery studies in the modelling and subsequent prediction of intestinal absorption for drug candidates. To bridge this gap, in this study, experimental membrane permeability data were measured for current and former drug substances with a parallel artificial membrane permeability assay (PAMPA) at different pH values (3, 5, 7.4 and 9). The presented data are in good agreement with human intestinal absorption, showing a clear influence of pH on the efficiency of intestinal absorption. For the measured data, simple and general quantitative structure-activity relationships (QSARs) were developed for each pH that makes it possible to predict the pH profiles for passive membrane permeability (i.e., a pH-permeability profile), and these predictions coincide well with the experimental data. QSARs are also proposed for the data series of highest and intrinsic membrane permeability. The molecular descriptors in the models were analysed and mechanistically related to the interaction pattern of permeability in membranes. In addition to the regression models, classification models are also proposed. All models were successfully validated and blind tested with external data. The models are available in the QsarDB repository (http://dx.doi.org/10.15152/QDB.203).

Transfer Behavior of the Weakly Acidic BCS Class II Drug Valsartan from the Stomach to the Small Intestine During Fasted and Fed States

The objective of this study was to investigate the transfer behavior of the weakly acidic BCS class II drug valsartan from the stomach to the small intestine during fasted and fed states. An in vitro transfer model previously introduced by Kostewicz et al. (J Pharm Pharmacol 56(1):43-51, 2004) based on a syringe pump and a USP paddle apparatus was used to determine the concentration profiles of valsartan in the small intestine. Donor phases of simulated gastric fluid during fasted (FaSSGF) and fed (FeSSGF) states were used to predisperse Diovan® tablets (160 mg valsartan). The initial concentrations of valsartan in FaSSGF and FeSSGF were 6.2 and 91.8%, respectively. Valsartan dispersions were then transferred to acceptor phases that simulate intestinal fluid and cover the physiological properties (pH, buffer capacity, and ionic strength) of the gastrointestinal fluid at a flow rate of 2 mL/min. The pH measurements were reported at time intervals corresponded to those of the transfer experiments to investigate the effect of percent dissolved of valsartan in the donor phase on lowering the pH of the acceptor phases. The f2 similarity test was used to compare the concentration profiles in the acceptor phases. In fasted state, the concentration of valsartan in the acceptor phases ranged between 33.1 and 89.4% after 240 min. Whereas in fed state, valsartan was fully dissolved in all acceptor phases within a range of 94.5-104.9% after 240 min. Therefore, the transfer model provides a useful screen for the concentrations of valsartan in the small intestine during fasted and fed states.

In Vitro Dissolution as a Tool for Formulation Selection: Telmisartan Two-Step IVIVC

The purpose of this investigation was to develop an exploratory two-step level A IVIVC for three telmisartan oral immediate release formulations, the reference product Micardis, and two generic formulations (X1 and X2). Correlation was validated with a third test formulation, Y1. Experimental solubility and permeability data were obtained to confirm that telmisartan is a class II compound under the Biopharmaceutic Classification System. Bioequivalence (BE) studies plasma profiles were combined using a previously published reference scaling procedure. X2 demonstrated in vivo BE, while X1 and Y1 failed to show BE due to the lower boundary of the 90% confidence interval for C_max being outside the acceptance limits. Average plasma profiles were deconvoluted by the Loo-Riegelman method to obtain the oral fractions absorbed ( f_a). Fractions dissolved ( f_diss) were obtained in several conditions in USP II and USP IV apparatus, and later, the results were compared in order to find the most biopredictive model, calculating the f₂ similarity factor. The apparatus and conditions showing the same rank order than in vivo data were selected for further refinement of conditions. A Levy plot was constructed to estimate the time scaling factor and to make both processes, dissolution and absorption, superimposable. The in vitro dissolution experiment that reflected more accurately the in vivo behavior of the different formulations of telmisartan employed the USP IV dissolution apparatus and a dissolution environment with a flow rate of 8 mL/min and a three-step pH change, from 1.2 to 4.5 and 6.8, with a 0.05% of Tween 80. Thus, these conditions gave rise to a biopredictive dissolution test. This new model is able to predict the formulation differences in dissolution that were previously observed in vivo, which could be used as a risk-analysis tool for formulation selection in future bioequivalence trials.

In vitro characterization of ritonavir formulations and correlation to in vivo performance in dogs

Ritonavir (RTV) is a weakly basic drug with a pH-dependent solubility. In vitro characterization of dissolution and supersaturation behaviors of three PEG-8000 based amorphous solid dispersions (ASD) and a physical blend (PB) with crystalline drug were performed in the biomimetic media (e.g., FaSSGF, FaSSIF, FaSSIF-V2). A two-stage dissolution test and a biphasic dissolution-partition test at the small scale (referred as to biphasic test) were employed with intention to examine the in vitro and in vivo relationship (IVIVR) with retrospective PK data in dog model. The two-stage dissolution test revealed a high degree of supersaturation of RTV from these ASDs accompanied by the occurrence of liquid-liquid phase separation (LLPS) in the biomimetic media. A rapid decrease of apparent RTV concentrations of these ASDs was associated with significant precipitation upon the pH shift of the dissolution medium, revealing the important role of "the gastric stage". In comparison, the biphasic test revealed a lower degree of supersaturation of RTV that is attributed to removal of RTV through partition into octanol, acting as "the absorption compartment". These two dissolution tests provide characterization of the supersaturation state with a complex, dynamic interplay among dissolution, precipitation and partition processes. Results of both in vitro dissolution tests are in good agreement with in vivo results in dogs. In addition, three commercial generic RTV drug products were examined by the biphasic test. Agreement was also obtained between the RTV concentrations in octanol at 3 h from these generic drug products and their corresponding relative bioavailability in dogs.

In Vitro, in Silico, and in Vivo Assessments of Intestinal Precipitation and Its Impact on Bioavailability of a BCS Class 2 Basic Compound

In this study, a multipronged approach of in vitro experiments, in silico simulations, and in vivo studies was developed to evaluate the dissolution, supersaturation, precipitation, and absorption of three formulations of Compound-A, a BCS class 2 weak base with pH-dependent solubility. In in vitro 2-stage dissolution experiments, the solutions were highly supersaturated with no precipitation at the low dose but increasing precipitation at higher doses. No difference in precipitation was observed between the capsules and tablets. The in vitro precipitate was found to be noncrystalline with higher solubility than the crystalline API, and was readily soluble when the drug concentration was lowered by dilution. A gastric transit and biphasic dissolution (GTBD) model was developed to better mimic gastric transfer and intestinal absorption. Precipitation was also observed in GTBD, but the precipitate redissolved and partitioned into the organic phase. In vivo data from the phase 1 clinical trial showed linear and dose proportional PK for the formulations with no evidence of in vivo precipitation. While the in vitro precipitation observed in the 2-stage dissolution appeared to overestimate in vivo precipitation, the GTBD model provided absorption profiles consistent with in vivo data. In silico simulation of plasma concentrations by GastroPlus using biorelevant in vitro dissolution data from the tablets and capsules and assuming negligible precipitation was in line with the observed in vivo profiles of the two formulations. The totality of data generated with Compound-A indicated that the bioavailability differences among the three formulations were better explained by the differences in gastric dissolution than intestinal precipitation. The lack of intestinal precipitation was consistent with several other BCS class 2 basic compounds in the literature for which highly supersaturated concentrations and rapid absorption were also observed.

An inert 3D emulsification device for individual precipitation and concentration of amorphous drug nanoparticles

Nanosizing increases the specific surface of drug particles, leading to faster dissolution inside the organism and improving the bioavailability of poorly water-soluble drugs. A novel approach for the preparation of drug nanoparticles in water using chemically inert microfluidic emulsification devices is presented in this paper. A lithographic fabrication sequence was established, allowing fabrication of intersecting and coaxial channels of different depths in glass as is required for 3D flow-focusing. Fenofibrate was used as a model for active pharmaceutical ingredients with very low water solubility in the experiments. It was dissolved in ethyl acetate and emulsified in water, as allowed by the 3D flow-focusing geometry. In the thread formation regime, the drug solution turned into monodisperse droplets of sizes down to below 1 μm. Fast supersaturation occurs individually in each droplet, as the disperse phase solvent progressively diffuses into the surrounding water. Liquid antisolvent precipitation results in highly monodisperse and amorphous nanoparticles of sizes down to 128 nm which can be precisely controlled by the continuous and disperse phase pressure. By comparing optically measured droplet sizes with particle sizes by dynamic light scattering, we could confirm that exactly one particle forms in every droplet. Furthermore, a downstream on-chip concentration allowed withdrawal of major volumes of only the continuous phase fluid which enabled an increase of particle concentration by up to 250 times.

A lipophilic prodrug of Danshensu: preparation, characterization, and in vitro and in vivo evaluation

Danshensu [3-(3, 4-dihydroxyphenyl) lactic acid, DSS], one of the significant cardioprotective components, is extracted from the root of Salvia miltiorrhiza. In the present study, an ester prodrug of Danshensu (DSS), palmitoyl Danshensu (PDSS), was synthesized with the aim to improve its oral bioavailability and prolong its half-life. The in vitro experiments were carried out to evaluate the physicochemical properties and stability of PDSS. Although the solubility of PDSS in water was only 0.055 mg·mL^-1, its solubility in FaSSIF and FeSSIF reached 4.68 and 9.08 mg·mL^-1, respectively. Octanol-water partition coefficient (log P) was increased from -2.48 of DSS to 1.90 of PDSS. PDSS was relatively stable in the aqueous solution in pH range from 5.6 to 7.4. Furthermore, the pharmacokinetics in rats was evaluated after oral administration of PDSS and DSS. AUC and t_1/2 of PDSS were enhanced up to 9.8-fold and 2.2-fold, respectively, compared to that of DSS. C_max was 1.67 ± 0.11 μg·mL^-1 for PDSS and 0.81 ± 0.06 μg·mL^-1 for DSS. Thus, these results demonstrated that PDSS had much higher oral bioavailability and longer circulation time than its parent drug.

RYGB and Drug Disposition: How to Do Better? Analysis of Pharmacokinetic Studies and Recommendations for Clinical Practice

An important issue in the follow-up of patients with bariatric surgery remains to determine whether their therapeutic management should be different after surgery. In this article, we first reviewed all pharmacokinetic studies involving at least four subjects who underwent the Roux-en-Y gastric bypass (RYGB) bariatric surgery. Twenty-five publications were selected and, overall, 25 drugs were studied. Drug solubility and permeability parameters for each drug were defined using different parameters or classifications. Increased rates of oral drug absorption were predominantly observed. Conversely, drug exposure differed from one drug to another. Considering the galenic formulation and the Biopharmaceutics Classification System (BCS) class may help the prediction of oral drug exposure outcome after RYGB. We propose a strategy aiming to guide prescription and drug monitoring in patients with RYGB. But further research is clearly needed due to the unique characteristics of the bariatric population. Priority should be given to drugs that do not have clinical or biological surrogates for dose adaptation.

Biomimetic Dissolution: A Tool to Predict Amorphous Solid Dispersion Performance

The presented study describes the development of a membrane permeation non-sink dissolution method that can provide analysis of complete drug speciation and emulate the in vivo performance of poorly water-soluble Biopharmaceutical Classification System class II compounds. The designed membrane permeation methodology permits evaluation of free/dissolved/unbound drug from amorphous solid dispersion formulations with the use of a two-cell apparatus, biorelevant dissolution media, and a biomimetic polymer membrane. It offers insight into oral drug dissolution, permeation, and absorption. Amorphous solid dispersions of felodipine were prepared by hot melt extrusion and spray drying techniques and evaluated for in vitro performance. Prior to ranking performance of extruded and spray-dried felodipine solid dispersions, optimization of the dissolution methodology was performed for parameters such as agitation rate, membrane type, and membrane pore size. The particle size and zeta potential were analyzed during dissolution experiments to understand drug/polymer speciation and supersaturation sustainment of felodipine solid dispersions. Bland-Altman analysis was performed to measure the agreement or equivalence between dissolution profiles acquired using polymer membranes and porcine intestines and to establish the biomimetic nature of the treated polymer membranes. The utility of the membrane permeation dissolution methodology is seen during the evaluation of felodipine solid dispersions produced by spray drying and hot melt extrusion. The membrane permeation dissolution methodology can suggest formulation performance and be employed as a screening tool for selection of candidates to move forward to pharmacokinetic studies. Furthermore, the presented model is a cost-effective technique.

In Vivo Dissolution and Systemic Absorption of Immediate Release Ibuprofen in Human Gastrointestinal Tract under Fed and Fasted Conditions

In vivo drug dissolution in the gastrointestinal (GI) tract is largely unmeasured. The purpose of this clinical study was to evaluate the in vivo drug dissolution and systemic absorption of the BCS class IIa drug ibuprofen under fed and fasted conditions by direct sampling of stomach and small intestinal luminal content. Expanding current knowledge of drug dissolution in vivo will help to establish physiologically relevant in vitro models predictive of drug dissolution. A multilumen GI catheter was orally inserted into the GI tract of healthy human subjects. Subjects received a single oral dose of ibuprofen (800 mg tablet) with 250 mL of water under fasting and fed conditions. The GI catheter facilitated collection of GI fluid from the stomach, duodenum, and jejunum. Ibuprofen concentration in GI fluid supernatant and plasma was determined by LC-MS/MS. A total of 23 subjects completed the study, with 11 subjects returning for an additional study visit (a total of 34 completed study visits). The subjects were primarily white (61%) and male (65%) with an average age of 30 years. The subjects had a median [min, max] weight of 79 [52, 123] kg and body mass index of 25.7 [19.4, 37.7] kg/m². Ibuprofen plasma levels were higher under fasted conditions and remained detectable for 28 h under both conditions. The AUC_0-24 and C_max were lower in fed subjects vs fasted subjects, and T_max was delayed in fed subjects vs fasted subjects. Ibuprofen was detected immediately after ingestion in the stomach under fasting and fed conditions until 7 h after dosing. Higher levels of ibuprofen were detected in the small intestine soon after dosing in fasted subjects compared to fed. In contrast to plasma drug concentration, overall gastric concentrations remained higher under fed conditions due to increased gastric pH vs fasting condition. The gastric pH increased to near neutrality after feedingbefore decreasing to acidic levels after 7 h. Induction of the fed state reduced systemic levels but increased gastric levels of ibuprofen, which suggest that slow gastric emptying and transit dominate the effect for plasma drug concentration. The finding of high levels of ibuprofen in stomach and small intestine 7 h post dosing was unexpected. Future work is needed to better understand the role of various GI parameters, such as motility and gastric emptying, on systemic ibuprofen levels in order to improve in vitro predictive models.

Low Buffer Capacity and Alternating Motility along the Human Gastrointestinal Tract: Implications for in Vivo Dissolution and Absorption of Ionizable Drugs

In this study, we determined the pH and buffer capacity of human gastrointestinal (GI) fluids (aspirated from the stomach, duodenum, proximal jejunum, and mid/distal jejunum) as a function of time, from 37 healthy subjects after oral administration of an 800 mg immediate-release tablet of ibuprofen (reference listed drug; RLD) under typical prescribed bioequivalence (BE) study protocol conditions in both fasted and fed states (simulated by ingestion of a liquid meal). Simultaneously, motility was continuously monitored using water-perfused manometry. The time to appearance of phase III contractions (i.e., housekeeper wave) was monitored following administration of the ibuprofen tablet. Our results clearly demonstrated the dynamic change in pH as a function of time and, most significantly, the extremely low buffer capacity along the GI tract. The buffer capacity on average was 2.26 μmol/mL/ΔpH in fasted state (range: 0.26 and 6.32 μmol/mL/ΔpH) and 2.66 μmol/mL/ΔpH in fed state (range: 0.78 and 5.98 μmol/mL/ΔpH) throughout the entire upper GI tract (stomach, duodenum, and proximal and mid/distal jejunum). The implication of this very low buffer capacity of the human GI tract is profound for the oral delivery of both acidic and basic active pharmaceutical ingredients (APIs). An in vivo predictive dissolution method would require not only a bicarbonate buffer but also, more significantly, a low buffer capacity of dissolution media to reflect in vivo dissolution conditions.

Mechanistic Oral Absorption Modeling and Simulation for Formulation Development and Bioequivalence Evaluation: Report of an FDA Public Workshop

On May 19, 2016, the US Food and Drug Administration (FDA) hosted a public workshop, entitled “Mechanistic Oral Absorption Modeling and Simulation for Formulation Development and Bioequivalence Evaluation.”1 The topic of mechanistic oral absorption modeling, which is one of the major applications of physiologically based pharmacokinetic (PBPK) modeling and simulation, focuses on predicting oral absorption by mechanistically integrating gastrointestinal transit, dissolution, and permeation processes, incorporating systems, active pharmaceutical ingredient (API), and the drug product information, into a systemic mathematical whole‐body framework.2

Developing Quantitative In Vitro-In Vivo Correlation for Fenofibrate Immediate-Release Formulations With the Biphasic Dissolution-Partition Test Method

This study is to evaluate 3 fenofibrate (FEN) formulations including Fournier® 200 mg capsule, Lipidil® 145 mg tablet, and a clinical HME 160 mg tablet by an in vitro biphasic method. Key experimental parameters were evaluated including the selection of biorelevant media, the United States Pharmacopeia IV flow rate, and the United States Pharmacopeia paddle speed. Varying the hydrodynamic condition resulted in a significant impact on FEN concentration time profiles in both aqueous and octanol phases for these formulations. In vivo pharmacokinetic profiles of the HME tablet, the Lipidil tablet, and Fournier capsule under the fasting and low-fat fed states are reported. Their corresponding absorption-time profiles were obtained through deconvolution by the Wagner-Nelson method. When fed state simulated intestinal fluid version 2 was used, the partitioned FEN amount-time profiles in octanol from the 3 formulations under an appropriate hydrodynamic condition exhibited a good agreement with their in vivo absorbed amount-time profiles, permitting a quantitative in vitro-in vivo correlation. When fasted state simulated intestinal fluid version 2 was used, partitioned FEN amounts into octanol from these formulations are significantly lower than those from in vivo data. Although no food effect was observed for both HME and Lipidil tablets, the positive food effect of the Fournier capsules significantly overestimated by the biphasic test.

Integrated TK-TD modeling for drug-induced concurrent tachycardia and QT changes in beagle dogs

Drug-induced cardiotoxicity, including tachycardia and QT prolongation, remains a major safety concern that needs to be identified and its risk mitigated in early stages of drug development. In the present study, an integrated toxicokinetic-toxicodynamic (TK-TD) modeling approach within a nonlinear mixed-effect modeling framework is applied to investigate concurrent abnormal heart rate and QT changes in three beagle dogs, using a Novartis internal compound (NVS001) as the case example. By accounting for saturable drug absorption, circadian rhythms, drug-effect tolerance, and nonlinear rate-dependency of QT interval, the dynamic TK-TD model captures the experimentally observed drug effects on heart rate and QT interval across a wide dosing range of NVS001 in beagle dogs. Further analyses reveal that the NVS001-induced QT prolongation observed in the low-dose groups is potentially caused by direct drug inhibition on the hERG channel, while the apparent QT shortening in the high-dose groups may be due to strong rate-dependency of QT at high heart rates. This study also suggests that the TK-TD model can be used to identify direct drug effects on the non-rate-dependent QT component by dissociating QT changes from tachycardia and deriving a new QT correction method. The integrated TK-TD model presented here may serve as a novel quantitative framework for evaluating drug-induced concurrent changes in heart rate and QT to potentially facilitate preclinical and clinical safety studies.

Pokharkar V. Understanding peroral absorption: regulatory aspects and contemporary approaches to tackling solubility and permeability hurdles

Oral drug absorption is a process influenced by the physicochemical and biopharmaceutical properties of the drug and its inter-relationship with the gastrointestinal tract. Drug solubility, dissolution and permeability across intestinal barrier are the key parameters controlling absorption. This review provides an overview of the factors that affect drug absorption and the classification of a drug on the basis of solubility and permeability. The biopharmaceutical classification system (BCS) was introduced in early 90׳s and is a regulatory tool used to predict bioavailability problems associated with a new entity, thereby helping in the development of a drug product. Strategies to combat solubility and permeability issues are also discussed.

The impact of supersaturation level for oral absorption of BCS class IIb drugs, dipyridamole and ketoconazole, using in vivo predictive dissolution system: Gastrointestinal Simulator (GIS)

The development of formulations and the assessment of oral drug absorption for Biopharmaceutical Classification System (BCS) class IIb drugs is often a difficult issue due to the potential for supersaturation and precipitation in the gastrointestinal (GI) tract. The physiological environment in the GI tract largely influences in vivo drug dissolution rates of those drugs. Thus, those physiological factors should be incorporated into the in vitro system to better assess in vivo performance of BCS class IIb drugs. In order to predict oral bioperformance, an in vitro dissolution system with multiple compartments incorporating physiologically relevant factors would be expected to more accurately predict in vivo phenomena than a one-compartment dissolution system like USP Apparatus 2 because, for example, the pH change occurring in the human GI tract can be better replicated in a multi-compartmental platform. The Gastrointestinal Simulator (GIS) consists of three compartments, the gastric, duodenal and jejunal chambers, and is a practical in vitro dissolution apparatus to predict in vivo dissolution for oral dosage forms. This system can demonstrate supersaturation and precipitation and, therefore, has the potential to predict in vivo bioperformance of oral dosage forms where this phenomenon may occur. In this report, in vitro studies were performed with dipyridamole and ketoconazole to evaluate the precipitation rates and the relationship between the supersaturation levels and oral absorption of BCS class II weak base drugs. To evaluate the impact of observed supersaturation levels on oral absorption, a study utilizing the GIS in combination with mouse intestinal infusion was conducted. Supersaturation levels observed in the GIS enhanced dipyridamole and ketoconazole absorption in mouse, and a good correlation between their supersaturation levels and their concentration in plasma was observed. The GIS, therefore, appears to represent in vivo dissolution phenomena and demonstrate supersaturation and precipitation of dipyridamole and ketoconazole. We therefore conclude that the GIS has been shown to be a good biopredictive tool to predict in vivo bioperformance of BCS class IIb drugs that can be used to optimize oral formulations.

In silico-in vitro-in vivo studies of experimentally designed carvedilol loaded silk fibroin-casein nanoparticles using physiological based pharmacokinetic model

The study aimed to design and develop carvedilol loaded silk fibroin-casein nanoparticles using 3² full factorial design. Silk fibroin and casein concentration were selected as the independent variables and their effect were observed on dependent variables: particle size, polydispersity index, encapsulation efficiency, drug release, and dissolution efficiency. The developed optimized formulation was characterized using fourier transform infrared spectroscopy, differential scanning calorimetry, and Powder X-ray diffraction. Surface morphology of optimized formulation using scanning electron microscopy, transmission electron microscopy, and atomic force microscopy revealed spherical nature of particles without any evidence of aggregation. The optimized formulation showed a 2.04-fold increase in C_max, and 6.87-fold increase in bioavailability as compared to aqueous suspension. The formulation showed sustained release as confirmed by increases in mean residence time. The in vivo in silico simulation using physiologically based pharmacokinetics (PBPK) model and population simulation (100 subjects) revealed a reasonable degree of superimposition of simulated and observed pharmacokinetic parameters based on overall fold error (≤2.0). The enhanced bioavailability with sustained effect demonstrates potential of silk fibroin as an alternative carrier for drug delivery and presents Gastoplus™ as efficient tool for in vivo in silico simulations.

A solid self-nanoemulsifying system of the BCS class IIb drug dabigatran etexilate to improve oral bioavailability

Aim: To develop dabigatran etexilate (DE)-loaded self-nanoemulsifying drug delivery systems (SNEDDS) for the prevention of stroke and thromboembolism. Materials & methods: SNEDDS were optimized by ternary phase diagrams and then further solidified into dispersible tablets. In vitro dissolution was analyzed by a phase distribution study. In situ absorption and in vivo pharmacokinetic studies were tested in male Sprague-Dawley rats. Results: The phase distribution study showed that more than 60% of DE was retained in the oil phase. Dissolution rate was dramatically enhanced without significant precipitation (<30%) in simulated intestinal fluid. Optimized SNEDDS had 531.80% relative bioavailability compared with Pradaxa® capsules (a commercial DE product). Conclusion: The developed SNEDDS are promising materials for improving the dissolution and oral bioavailability of BCS class IIb drugs.

Discriminative Dissolution Method for Benzoyl Metronidazole Oral Suspension

A dissolution method for benzoyl metronidazole (BMZ) oral suspensions was developed and validated using a high-performance liquid chromatography (HPLC) method. After determination of sink conditions, dissolution profiles were evaluated using different dissolution media and agitation speeds. The sample insertion mode in dissolution media was also evaluated. The best conditions were obtained using a paddle, 50 rpm stirring speed, simulated gastric fluid (without pepsin) as the dissolution medium, and sample insertion by a syringe. These conditions were suitable for providing sink conditions and discriminatory power between different formulations. Through the tested conditions, the results can be considered specific, linear, precise, accurate, and robust. The dissolution profiles of five samples were compared using the similarity factor (f 2) and dissolution efficiency. The dissolution kinetics were evaluated and described by the Weibull model. Whereas there is no monograph for this pharmaceutical formulation, the dissolution method proposed can be considered suitable for quality control and dissolution profile comparison of different commercial formulations.

pH-Dependent Solubility and Dissolution Behavior of Carvedilol--Case Example of a Weakly Basic BCS Class II Drug

The objective of this study was to investigate the pH-dependent solubility and dissolution of weakly basic Biopharmaceutical Classification Systems (BCS) class II drugs, characterized by low solubility and high permeability, using carvedilol, a weak base with a pK a value of 7.8, as a model drug. A series of solubility and in vitro dissolution studies was carried out using media that simulate the gastric and intestinal fluids and cover the physiological pH range of the GI from 1.2 to 7.8. The effect of ionic strength, buffer capacity, and buffer species of the dissolution media on the solubility and dissolution behavior of carvedilol was also investigated. The study revealed that carvedilol exhibited a typical weak base pH-dependent solubility profile with a high solubility at low pH (545.1-2591.4 μg/mL within the pH range 1.2-5.0) and low solubility at high pH (5.8-51.9 μg/mL within the pH range 6.5-7.8). The dissolution behavior of carvedilol was consistent with the solubility results, where carvedilol release was complete (95.8-98.2% released within 60 min) in media simulating the gastric fluid (pH 1.2-5.0) and relatively low (15.9-86.2% released within 240 min) in media simulating the intestinal fluid (pH 6.5-7.8). It was found that the buffer species of the dissolution media may influence the solubility and consequently the percentage of carvedilol released by forming carvedilol salts of varying solubilities. Carvedilol solubility and dissolution decreased with increasing ionic strength, while lowering the buffer capacity resulted in a decrease in carvedilol solubility and dissolution rate.

Cyclodextrin and Meglumine-Based Microemulsions as a Poorly Water-Soluble Drug Delivery System

Cyclodextrins (CDs) and meglumine (MEG) are pharmaceutical excipients widely used to improve solubility of poorly water-soluble drugs. The purpose of this work was to study the effect of CDs or MEG on the internal microstructure of soya oil-based O/W microemulsions (MEs) and on the modulation of the solubility and release rate of Class II model hydrophobic drugs, sulfamerazine and indomethacin. The pseudoternary phase diagrams revealed that higher proportions of oil phase, as well as the presence of β-cyclodextrin (ßCD), methyl-ßCD, and MEG, favored the incorporation of the drugs. The conductivity studies, particle size, and zeta potential analysis showed that the O/W ME structure remained unaffected and that the ME presented reduced droplet sizes after the incorporation of the ligands. The drug-component interactions were assessed by proton nuclear magnetic resonance studies. The highest incorporations of sulfamerazine (35.6 mg/mL) and indomethacin (73.1 mg/mL) were obtained with the ME with W = 5%, MEG and W = 1.8% ßCD in a phosphate buffer solution of pH 8, respectively. In addition, the ligands in ME significantly enhanced the released amount of the drugs, probably due to a solubilizing effect that facilitates the drug to penetrate the unstirred water layer adjacent to membranes.

Intestinal solubility and absorption of poorly water soluble compounds: predictions, challenges and solutions

We have explored for which type of compounds biorelevant dissolution profiling in simulated intestinal fluids would accurately predict solubility in human intestinal fluid. In total, 474 solubility values in simulated and aspirated human intestinal fluid for 78 drugs were compiled and analyzed. Significant solubilization in the colloidal structures was obtained in fasted and fed state fluids for drug compounds with a logD(oct)>3. Highly lipophilic compounds with high melting points (Tm > 200 °C) could also be significantly solubilized, but typically such compounds had solubility values in the lower µg/ml range also in the presence of the colloidal structures. On the basis of our analysis, compounds with a logD(oct)>3 should be explored in biorelevant dissolution media to better predict in vivo performance after oral dosing.