Analysis of the enhanced oral bioavailability of fenofibrate lipid formulations in fasted humans using an in vitro-in silico-in vivo approach

In Silico Modeling Approaches Coupled with In Vitro Characterization in Predicting In Vivo Performance of Drug Delivery System Formulations

Optimization of the in vivo performance of dosage forms in humans is essential in developing not only conventional formulations but also drug delivery system (DDS) formulations. Although animal experiments are still useful for these formulations, in silico approaches have become increasingly important for DDS formulations with regard to species-specific differences in physiology that can affect the in vivo performance of dosage forms between animals and humans. Furthermore, it is also important to couple in vitro characterizations with in silico models to predict in vivo performance in humans precisely. In this review article, I summarized in vitro-in silico approaches to predicting the in vivo performance of oral DDS formulations (amorphous solid dispersions, lipid-based formulations, nanosized formulations, cyclodextrins-based formulations, sustained release products, enteric coat products, and orally disintegrating tablets) and parenteral DDS formulations (cyclodextrins-based formulations, liposomes, and inhaled formulations).

Leveraging the use of in vitro and computational methods to support the development of enabling oral drug products: An InPharma commentary

Due to the strong tendency towards poorly soluble drugs in modern development pipelines, enabling drug formulations such as amorphous solid dispersions, cyclodextrins, co-crystals and lipid-based formulations are frequently applied to solubilize or generate supersaturation in gastrointestinal fluids, thus enhancing oral drug absorption. Although many innovative in vitro and in silico tools have been introduced in recent years to aid development of enabling formulations, significant knowledge gaps still exist with respect to how best to implement them. As a result, the development strategy for enabling formulations varies considerably within the industry and many elements of empiricism remain. The InPharma network aims to advance a mechanistic, animal-free approach to the assessment of drug developability. This commentary focuses current status and next steps that will be taken in InPharma to identify and fully utilize 'best practice' in vitro and in silico tools for use in physiologically based biopharmaceutic models.

Advanced In Vivo Prediction by Introducing Biphasic Dissolution Data into PBPK Models

Coupling biorelevant in vitro dissolution with in silico physiological-based pharmacokinetic (PBPK) tools represents a promising method to describe and predict the in vivo performance of drug candidates in formulation development including non-passive transport, prodrug activation, and first-pass metabolism. The objective of the present study was to assess the predictability of human pharmacokinetics by using biphasic dissolution results obtained with the previously established BiPHa+ assay and PBPK tools. For six commercial drug products, formulated by different enabling technologies, the respective organic partitioning profiles were processed with two PBPK in silico modeling tools, namely PK-Sim and GastroPlus^®, similar to extended-release dissolution profiles. Thus, a mechanistic dissolution/precipitation model of the assessed drug products was not required. The developed elimination/distribution models were used to simulate the pharmacokinetics of the evaluated drug products and compared with available human data. In essence, an in vitro to in vivo extrapolation (IVIVE) was successfully developed. Organic partitioning profiles obtained from the BiPHa+ dissolution analysis enabled highly accurate predictions of the pharmacokinetic behavior of the investigated drug products. In addition, PBPK models of (pro-)drugs with pronounced first-pass metabolism enabled adjustment of the solely passive diffusion predicting organic partitioning profiles, and increased prediction accuracy further.

Opportunities and challenges of physiologically based pharmacokinetic modeling in drug delivery

Physiologically based pharmacokinetic (PBPK) modeling is an important in silico tool to bridge drug properties and in vivo PK behaviors during drug development. Over the recent decade, the PBPK method has been largely applied to drug delivery systems (DDS), including oral, inhaled, transdermal, ophthalmic, and complex injectable products. The related therapeutic agents have included small-molecule drugs, therapeutic proteins, nucleic acids, and even cells. Simulation results have provided important insights into PK behaviors of new dosage forms, which strongly support drug regulation. In this review, we comprehensively summarize recent progress in PBPK applications in drug delivery, which shows large opportunities for facilitating drug development. In addition, we discuss the challenges of applying this methodology from a practical viewpoint.

In vitro and in vivo correlation for lipid-based formulations: Current status and future perspectives

Lipid-based formulations (LBFs) have demonstrated a great potential in enhancing the oral absorption of poorly water-soluble drugs. However, construction of in vitro and in vivo correlations (IVIVCs) for LBFs is quite challenging, owing to a complex in vivo processing of these formulations. In this paper, we start with a brief introduction on the gastrointestinal digestion of lipid/LBFs and its relation to enhanced oral drug absorption; based on the concept of IVIVCs, the current status of in vitro models to establish IVIVCs for LBFs is reviewed, while future perspectives in this field are discussed. In vitro tests, which facilitate the understanding and prediction of the in vivo performance of solid dosage forms, frequently fail to mimic the in vivo processing of LBFs, leading to inconsistent results. In vitro digestion models, which more closely simulate gastrointestinal physiology, are a more promising option. Despite some successes in IVIVC modeling, the accuracy and consistency of these models are yet to be validated, particularly for human data. A reliable IVIVC model can not only reduce the risk, time, and cost of formulation development but can also contribute to the formulation design and optimization, thus promoting the clinical translation of LBFs.

Biorelevant dissolution testing and physiologically based absorption modeling to predict in vivo performance of supersaturating drug delivery systems

Supersaturating drug delivery systems (SDDS) enhance the oral absorption of poorly water-soluble drugs by achieving a supersaturated state in the gastrointestinal tract. The maintenance of a supersaturated state is decided by the complex interplay among inherent properties of drug, excipients and physiological conditions of gastrointestinal tract. The biopharmaceutical advantage through SDDS can be mechanistically investigated by coupling biopredictive dissolution testing with physiologically based absorption modeling (PBAM). However, the development of biopredictive dissolution methods possess challenges due to concurrent dissolution, supersaturation, precipitation, and possible redissolution of precipitates during gastrointestinal transit of SDDS. In this comprehensive review, our effort is to critically assess the current state-of-knowledge and provide future directions for PBAM of SDDS. The review outlines various methods used to retrieve physiologically relevant values for input parameters like solubility, dissolution, precipitation, lipid-digestion and permeability of SDDS. SDDS-specific parameterization includes solubility values corresponding to apparent physical form, dissolution in physiologically relevant volumes with biorelevant media, and transfer experiments to incorporate precipitation kinetics. Interestingly, the lack of experimental permeability values and modification of absorption flux through SDDS possess the additional challenge for its PBAM. Supersaturation triggered permeability modifications are reported to fit the observed plasma concentration-time profile. Hence, the experimental insights on good fitting with modified permeability can be potential area of future research for the development of in vitro methods to reliably predict oral absorption of SDDS.

Predicting the environmental emissions arising from conventional and nanotechnology-related pharmaceutical drug products

Today, environmental pollution with pharmaceutical drugs and their metabolites poses a major threat to the aquatic ecosystems. Active substances such as fenofibrate, are processed to pharmaceutical drug formulations before they are degraded by the human body and released into the wastewater. Compared to the conventional product Lipidil® 200, the pharmaceutical product Lipidil 145 One® and Ecocaps take advantage of nanotechnology to improve uptake and bioavailability of the drug in humans. In the present approach, a combination of in vitro drug release studies and physiologically-based biopharmaceutics modeling was applied to calculate the emission of three formulations of fenofibrate (Lipidil® 200, Lipidil 145 One®, Ecocaps) into the environment. Special attention was paid to the metabolized and non-metabolized fractions and their individual toxicity, as well as to the emission of nanomaterials. The fish embryo toxicity test revealed a lower aquatic toxicity for the metabolite fenofibric acid and therefore an improved toxicity profile. When using the microparticle formulation Lipidil® 200, an amount of 126 mg of non-metabolized fenofibrate was emitted to the environment. Less than 0.05% of the particles were in the lower nanosize range. For the nanotechnology-related product Lipidil 145 One®, the total drug emission was reduced by 27.5% with a nanomaterial fraction of approximately 0.5%. In comparison, the formulation prototype Ecocaps reduced the emission of fenofibrate by 42.5% without any nanomaterials entering the environment. In a streamlined life cycle assessment, the lowered dose in combination with a lowered drug-to-metabolite ratio observed for Ecocaps led to a reduction of the full life cycle impacts of fenofibrate with a reduction of 18% reduction in the global warming potential, 61% in ecotoxicity, and 15% in human toxicity. The integrated environmental assessment framework highlights the outstanding potential of advanced modeling technologies to determine environmental impacts of pharmaceuticals during early drug development using preclinical in vitro data.

Self-Nano-Emulsifying Drug-Delivery Systems: From the Development to the Current Applications and Challenges in Oral Drug Delivery

Approximately one third of newly discovered drug molecules show insufficient water solubility and therefore low oral bio-availability. Self-nano-emulsifying drug-delivery systems (SNEDDSs) are one of the emerging strategies developed to tackle the issues associated with their oral delivery. SNEDDSs are composed of an oil phase, surfactant, and cosurfactant or cosolvent. SNEDDSs characteristics, their ability to dissolve a drug, and in vivo considerations are determinant factors in the choice of SNEDDSs excipients. A SNEDDS formulation can be optimized through phase diagram approach or statistical design of experiments. The characterization of SNEDDSs includes multiple orthogonal methods required to fully control SNEDDS manufacture, stability, and biological fate. Encapsulating a drug in SNEDDSs can lead to increased solubilization, stability in the gastro-intestinal tract, and absorption, resulting in enhanced bio-availability. The transformation of liquid SNEDDSs into solid dosage forms has been shown to increase the stability and patient compliance. Supersaturated, mucus-permeating, and targeted SNEDDSs can be developed to increase efficacy and patient compliance. Self-emulsification approach has been successful in oral drug delivery. The present review gives an insight of SNEDDSs for the oral administration of both lipophilic and hydrophilic compounds from the experimental bench to marketed products.

Novel Biphasic Lipolysis Method To Predict in Vivo Performance of Lipid-Based Formulations

The absence of an intestinal absorption sink is a significant weakness of standard in vitro lipolysis methods, potentially leading to poor prediction of in vivo performance and an overestimation of drug precipitation. In addition, the majority of the described lipolysis methods only attempt to simulate intestinal conditions, thus overlooking any supersaturation or precipitation of ionizable drugs as they transition from the acidic gastric environment to the more neutral conditions of the intestine. The aim of this study was to develop a novel lipolysis method incorporating a two-stage gastric-to-intestinal transition and an absorptive compartment to reliably predict in vivo performance of lipid-based formulations (LBFs). Drug absorption was mimicked by in situ quantification of drug partitioning into a decanol layer. The method was used to characterize LBFs from four studies described in the literature, involving three model drugs (i.e., nilotinib, fenofibrate, and danazol) where in vivo bioavailability data have previously been reported. The results from the novel biphasic lipolysis method were compared to those of the standard pH-stat method in terms of reliability for predicting the in vivo performance. For three of the studies, the novel biphasic lipolysis method more reliably predicted the in vivo bioavailability compared to the standard pH-stat method. In contrast, the standard pH-stat method was found to produce more predictive results for one study involving a series of LBFs composed of the soybean oil, glyceryl monolinoleate (Maisine CC), Kolliphor EL, and ethanol. This result was surprising and could reflect that increasing concentrations of ethanol (as a cosolvent) in the formulations may have resulted in greater partitioning of the drug into the decanol absorptive compartment. In addition to the improved predictivity for most of the investigated systems, this biphasic lipolysis method also uses in situ analysis and avoids time- and resource-intensive sample analysis steps, thereby facilitating a higher throughput capacity and biorelevant approach for characterization of LBFs.

Amelioration of lipophilic compounds in regards to bioavailability as self-emulsifying drug delivery system (SEDDS)

Background

High lipophilicity and poor aqueous solubility are the endemic problems of new drug molecules. Sixty to seventy percent of these drugs are unable to solubilize completely in aqueous media, or have very low permeability. This hampers their oral absorption and further leads to their poor bioavailability. Various researches are in progress to overcome these limitations. Novel technologies like nano-carrier systems have become popular for improving the solubility of drugs.

Main body

Lipid-based formulations, among nano systems, are taking pace for the enhancement of solubility, oral absorption, and hence the bioavailability of drugs. Among the lipid formulations, self-emulsification systems are gaining popularity by offering various advantages to delivery systems. Self-emulsifying drug delivery systems (SEDDS) are isotropic blends of oil and surfactant/co-surfactants. These ingredients upon gentle agitation in aqueous media results in the formation of o/w emulsion. In spite of many works published in SEDDS, the major concerns of this article are to discuss the various approaches to formulate a good lipid-based carrier system for poorly aqueous soluble drugs, role of various polymers, and their categories used in the formulation along-with the modern technologies used for enhancing the stability of liquid SEDDS. This review majorly focuses upon the problems related to the poor aqueous solubility of the newer lipid molecules and the solutions to overcome their solubility and in addition bioavailability.

Conclusion

As per the researches done in formulation and optimization of SEDDS for the enhancement of bioavailability of lipophilic molecules, it can be stated that the aqueous solubility as well as bioavailability can be increased by many folds compared to their marketed or other oral formulations.

Suitability of Artificial Membranes in Lipolysis-Permeation Assays of Oral Lipid-Based Formulations

PURPOSE

To evaluate the performance of artificial membranes in in vitro lipolysis-permeation assays useful for absorption studies of drugs loaded in lipid-based formulations (LBFs).

METHODS

Polycarbonate as well as PVDF filters were treated with hexadecane, or lecithin in n-dodecane solution (LiDo) to form artificial membranes. They were thereafter used as absorption membranes separating two compartments mimicking the luminal and serosal side of the intestine in vitro. Membranes were subjected to dispersions of an LBF that had been digested by porcine pancreatin and spiked with the membrane integrity marker Lucifer Yellow (LY). Three fenofibrate-loaded LBFs were used to explore the in vivo relevance of the assay.

RESULTS

Of the explored artificial membranes, only LiDo applied to PVDF was compatible with lipolysis by porcine pancreatin. Formulation ranking based on mass transfer in the LiDo model exposed was the same as drug release in single-compartment lipolysis. Ranking based on observed apparent permeability coefficients of fenofibrate with different LBFs were the same as those obtained in a cell-based model.

CONCLUSIONS

The LiDo membrane was able to withstand lipolysis for a sufficient assay period. However, the assay with porcine pancreatin as digestive agent did not predict the in vivo ranking of the assayed formulations better than existing methods. Comparison with a Caco-2 based assay method nonetheless indicates that the in vitro in vivo relationship of this cell-free model could be improved with alternative digestive agents.

A STELLA simulation model for in vitro dissolution testing of respirable size particles

In vitro dissolution testing is a useful quality control tool to discriminate the formulations and to approximate the in vivo drug release profiles. A dissolution apparatus has been custom-made for dissolution testing of dry powder formulations in a small volume of stationary medium (25 μL spread over 4.91 cm² area i.e. ~50 μm thick). To understand the system and predict the key parameters which influence the dissolution of respirable size particles, a simulation model was constructed using STELLA modeling software. Using this model, the permeation (dissolution followed by diffusion through the membrane) of two anti-tubercular drugs of differing solubilities, moxifloxacin (17.68 ± 0.85 mg mL^-1) and ethionamide (0.46 ± 0.02 mg mL^-1), from the respirable size particles and their diffusion from a solution were simulated. The simulated permeation profiles of moxifloxacin from solution and respirable size particles were similar, indicating fast dissolution of the particles. However, the simulated permeation profile of ethionamide from respirable size particles showed slower permeation compared to the solution indicating the slow dissolution of the respirable size particles of ethionamide. The sensitivity analysis suggested that increased mucus volume and membrane thickness decreased the permeation of drug. While this model was useful in predicting and distinguishing the dissolution behaviours of respirable size moxifloxacin and ethionamide, further improvement could be made using appropriate initial parameter values obtained by experiments.

Development and Characterization of a Self-Nanoemulsifying Drug Delivery System Comprised of Rice Bran Oil for Poorly Soluble Drugs

Poor aqueous solubility and low bioavailability are limiting factors in the oral delivery of lipophilic drugs. In a formulation approach to overcome these limitations, rice bran (RB) oil was evaluated as drug carrier in the development of self-nanoemulsifying drug delivery systems (SNEDDS). The performance of RB in formulations incorporating Kolliphor RH40 or Kolliphor EL as surfactants and Transcutol HP as cosolvent was compared to a common oil vehicle, corn oil (CO). Serial dilutions of the preconcentrates were performed in various media [distilled water and simulated intestinal fluids mimicking fasted state (FaSSIF) and fed state (FeSSIF)] and at different dilution ratios to simulate the in vivo droplets' behavior. The developed SNEDDS were assessed by means of phase separation, droplet size, polydispersity index, and ζ-potential. Complex ternary diagrams were constructed to identify compositions exhibiting monophasic behavior, droplet size < 100 nm, and polydispersity index (PDI) < 0.25. Multifactor analysis and response surface areas intended to determine the factors significantly affecting droplet size. The oil capacity to accommodate lipophilic drugs was assessed via fluorescence spectroscopy based on the solvatochromic behavior of Nile Red. Solubility studies were performed to prepare fenofibrate- and itraconazole-loaded SNEDDS and assess their droplet size, whereas dissolution experiments were conducted in simulated intestinal fluids. Caco-2 cell viability studies confirmed the safety of the SNEDDS formulations at 1:100 and 1:1000 dilutions after cell exposure in culture for 4 h. The obtained results showed similar performance between RB and CO supporting the potential of RB as oil vehicle for the effective oral delivery of lipophilic compounds.

Critical In Vitro Characterization Methods of Lipid-Based Formulations for Oral Delivery: a Comprehensive Review

Lipids have been extensively used in formulations to enhance dissolution and bioavailability of poorly water-soluble as well as water-soluble drug molecules. The digestion of lipid-based formulations, in the presence of bile salts, phospholipids, and cholesterol, changes the lipid composition in vivo, resulting in the formation of different colloidal phases in the intestine. Therefore, in vitro characterization and evaluation of such formulations are critical in developing a successful formulation. This review covers comprehensive discussion on in vitro characterization techniques such as solubility, drug entrapment, thermal characterization, dissolution, and digestion of lipid-based formulations.

Effect of Complexes and Microemulsions on the Permeability of Drugs: Determination Using a New Biomimetic Artificial Membrane

The aim of this work was to predict the permeability of two model drugs, sulfamerazine (SMR) and indomethacin (INM), and to determine the effect on their apparent permeabilities by complexation with cyclodextrins and/or meglumine or incorporation in microemulsions. Permeation experiments were performed using two-chamber diffusion cells with a new composition of bio-mimetic membrane composed of 80% of Lipoid® S100 and 20% of cholesterol in n-octanol 10% w/w solution, at 37 ± 0.5°C and 14,000 rpm. The predictive capacity of the permeability of passive diffusion absorbed compounds was evaluated using 20 drug standards and showed an exponential correlation between the apparent permeability coefficients (P_app) and the fraction absorbed percentages in humans (Fa%), with an R² value of 0.67942 and a constant value of - 4.1 ± 0.8. SMR and INM were classified as Class II and I, respectively, according to the Biopharmaceutical Classification System. These drugs were complexed and incorporated in microemulsions. The Fa% from all the drug products was higher than 90%. SMR in the complexes and both drugs in microemulsions were classified as highly soluble. Thus, SMR and INM incorporated in these pharmaceutical products could be classified as Class I.

The pig as a preclinical model for predicting oral bioavailability and in vivo performance of pharmaceutical oral dosage forms: a PEARRL review

OBJECTIVES

In pharmaceutical drug development, preclinical tests in animal models are essential to demonstrate whether the new drug is orally bioavailable and to gain a first insight into in vivo pharmacokinetic parameters that can subsequently be used to predict human values. Despite significant advances in the development of bio-predictive in vitro models and increasing ethical expectations for reducing the number of animals used for research purposes, there is still a need for appropriately selected pre-clinical in vivo testing to provide guidance on the decision to progress to testing in humans. The selection of the appropriate animal models is essential both to maximise the learning that can be obtained from such experiments and to avoid unnecessary testing in a range of species.

KEY FINDINGS

The present review, provides an insight into the suitability of the pig model for predicting oral bioavailability in humans, by comparing the conditions in the GIT. It also contains a comparison between the bioavailability of compounds dosed to both humans and pigs, to provide an insight into the relative correlation and examples on why a lack of correlation may be observed.

SUMMARY

While there is a general trend towards predicting human bioavailability from pig data, there is considerable variability in the data set, most likely reflecting species specific differences in individual drug metabolism. Nonetheless, the correlation between pigs vs. humans was comparable to that reported for dogs vs. humans. The presented data demonstrate the suitability of the pig as a preclinical model to predict bioavailability in human.

Development, current applications and future roles of biorelevant two-stage in vitro testing in drug development

Objectives

Various types of two stage in vitro testing have been used in a number of experimental settings. In addition to its application in quality control and for regulatory purposes, two-stage in vitro testing has also been shown to be a valuable technique to evaluate the supersaturation and precipitation behavior of poorly soluble drugs during drug development.

Key findings

The so-called ‘transfer model’, which is an example of two-stage testing, has provided valuable information about the in vivo performance of poorly soluble, weakly basic drugs by simulating the gastrointestinal drug transit from the stomach into the small intestine with a peristaltic pump. The evolution of the transfer model has resulted in various modifications of the experimental model set-up. Concomitantly, various research groups have developed simplified approaches to two-stage testing to investigate the supersaturation and precipitation behavior of weakly basic drugs without the necessity of using a transfer pump.

Summary

Given the diversity among the various two-stage test methods available today, a more harmonized approach needs to be taken to optimize the use of two stage testing at different stages of drug development.

Mesoporous silica-based dosage forms improve bioavailability of poorly soluble drugs in pigs: case example fenofibrate

Objectives

Mesoporous silicas (SLC) have demonstrated considerable potential to improve bioavailability of poorly soluble drugs by facilitating rapid dissolution and generating supersaturation. The addition of certain polymers can further enhance the dissolution of these formulations by preventing drug precipitation. This study uses fenofibrate as a model drug to investigate the performance of an SLC-based formulation, delivered with hydroxypropyl methylcellulose acetate succinate (HPMCAS) as a precipitation inhibitor, in pigs. The ability of biorelevant dissolution testing to predict the in vivo performance was also assessed.

Key findings

Fenofibrate-loaded mesoporous silica (FF-SLC), together with HPMCAS, displayed significant improvements in biorelevant dissolution tests relative to a reference formulation consisting of a physical mixture of crystalline fenofibrate with HPMCAS. In vivo assessment in fasted pigs demonstrated bioavailabilities of 86.69 ± 35.37% with combination of FF-SLC and HPMCAS in capsule form and 75.47 ± 14.58% as a suspension, compared to 19.92 ± 9.89% with the reference formulation. A positive correlation was identified between bioavailability and dissolution efficiency.

Conclusions

The substantial improvements in bioavailability of fenofibrate from the SLC-based formulations confirm the ability of this formulation strategy to overcome the dissolution and solubility limitations, further raising the prospects of a future commercially available SLC-based formulation.

In vitro dissolution models for the prediction of in vivo performance of an oral mesoporous silica formulation

Drug release from mesoporous silica systems has been widely investigated in vitro using USP Type II (paddle) dissolution apparatus. However, it is not clear if the observed enhanced in vitro dissolution can forecast drug bioavailability in vivo. In this study, the ability of different in vitro dissolution models to predict in vivo oral bioavailability in a pig model was examined. The fenofibrate-loaded mesoporous silica formulation was compared directly to a commercial reference product, Lipantil Supra®. Three in vitro dissolution methods were considered; USP Type II (paddle) apparatus, USP Type IV (flow-through cell) apparatus and a USP IV Transfer model (incorporating a SGF to FaSSIF-V2 media transfer). In silico modelling, using a physiologically based pharmacokinetic modelling and simulation software package (Gastroplus™), to generate in vitro/in vivo relationships, was also investigated. The study demonstrates that the in vitro dissolution performance of a mesoporous silica formulation varies depending on the dissolution apparatus utilised and experimental design. The findings show that the USP IV transfer model was the best predictor of in vivo bioavailability. The USP Type II (paddle) apparatus was not effective at forecasting in vivo behaviour. This observation is likely due to hydrodynamic differences between the two apparatus and the ability of the transfer model to better simulate gastrointestinal transit. The transfer model is advantageous in forecasting in vivo behaviour for formulations which promote drug supersaturation and as a result are prone to precipitation to a more energetically favourable, less soluble form. The USP IV transfer model could prove useful in future mesoporous silica formulation development. In silico modelling has the potential to assist in this process. However, further investigation is required to overcome the limitations of the model for solubility enhancing formulations.

Lipid-associated oral delivery: Mechanisms and analysis of oral absorption enhancement

The majority of newly discovered oral drugs are poorly water soluble, and co-administration with lipids has proven effective in significantly enhancing bioavailability of some compounds with low aqueous solubility. Yet, lipid-based delivery technologies have not been widely employed in commercial oral products. Lipids can impact drug transport and fate in the gastrointestinal (GI) tract through multiple mechanisms including enhancement of solubility and dissolution kinetics, enhancement of permeation through the intestinal mucosa, and triggering drug precipitation upon lipid emulsion depletion (e.g., by digestion). The effect of lipids on drug absorption is currently not quantitatively predictable, in part due to the multiple complex dynamic processes that can be impacted by lipids. Quantitative mechanistic analysis of the processes significant to lipid system function and overall impact on drug absorption can aid in the understanding of drug-lipid interactions in the GI tract and exploitation of such interactions to achieve optimal lipid-based drug delivery. In this review, we discuss the impact of co-delivered lipids and lipid digestion on drug dissolution, partitioning, and absorption in the context of the experimental tools and associated kinetic expressions used to study and model these processes. The potential benefit of a systems-based consideration of the concurrent multiple dynamic processes occurring upon co-dosing lipids and drugs to predict the impact of lipids on drug absorption and enable rational design of lipid-based delivery systems is presented.

Computational prediction of formulation strategies for beyond-rule-of-5 compounds

The physicochemical properties of some contemporary drug candidates are moving towards higher molecular weight, and coincidentally also higher lipophilicity in the quest for biological selectivity and specificity. These physicochemical properties move the compounds towards beyond rule-of-5 (B-r-o-5) chemical space and often result in lower water solubility. For such B-r-o-5 compounds non-traditional delivery strategies (i.e. those other than conventional tablet and capsule formulations) typically are required to achieve adequate exposure after oral administration. In this review, we present the current status of computational tools for prediction of intestinal drug absorption, models for prediction of the most suitable formulation strategies for B-r-o-5 compounds and models to obtain an enhanced understanding of the interplay between drug, formulation and physiological environment. In silico models are able to identify the likely molecular basis for low solubility in physiologically relevant fluids such as gastric and intestinal fluids. With this baseline information, a formulation scientist can, at an early stage, evaluate different orally administered, enabling formulation strategies. Recent computational models have emerged that predict glass-forming ability and crystallisation tendency and therefore the potential utility of amorphous solid dispersion formulations. Further, computational models of loading capacity in lipids, and therefore the potential for formulation as a lipid-based formulation, are now available. Whilst such tools are useful for rapid identification of suitable formulation strategies, they do not reveal drug localisation and molecular interaction patterns between drug and excipients. For the latter, Molecular Dynamics simulations provide an insight into the interplay between drug, formulation and intestinal fluid. These different computational approaches are reviewed. Additionally, we analyse the molecular requirements of different targets, since these can provide an early signal that enabling formulation strategies will be required. Based on the analysis we conclude that computational biopharmaceutical profiling can be used to identify where non-conventional gateways, such as prediction of 'formulate-ability' during lead optimisation and early development stages, are important and may ultimately increase the number of orally tractable contemporary targets.

50years of oral lipid-based formulations: Provenance, progress and future perspectives

Lipid based formulations (LBF) provide well proven opportunities to enhance the oral absorption of drugs and drug candidates that sit close to, or beyond, the boundaries of Lipinski's 'rule-of-five' chemical space. Advantages in permeability, efflux and presystemic metabolism are evident; however, the primary benefit is in increases in dissolution and apparent intestinal solubility for lipophilic, poorly water soluble drugs. This review firstly details the inherent advantages of LBF, their general properties and classification, and provides a brief retrospective assessment of the development of LBF over the past fifty years. More detailed analysis of the ability of LBF to promote intestinal solubilisation, supersaturation and absorption is then provided alongside review of the methods employed to assess formulation performance. Critical review of the ability of simple dispersion and more complex in vitro digestion methods to predict formulation performance subsequently reveals marked differences in the correlative ability of in vitro tests, depending on the properties of the drug involved. Notably, for highly permeable low melting drugs e.g. fenofibrate, LBF appear to provide significant benefit in all cases, and sustained ongoing solubilisation may not be required. In other cases, and particularly for higher melting point drugs such as danazol, where re-dissolution of crystalline precipitate drug is likely to be slow, correlations with ongoing solubilisation and supersaturation are more evident. In spite of their potential benefits, one limitation to broader use of LBF is low drug solubility in the excipients employed to generate formulations. Techniques to increase drug lipophilicity and lipid solubility are therefore explored, and in particular those methods that provide for temporary enhancement including lipophilic ionic liquid and prodrug technologies. The transient nature of these lipophilicity increases enhances lipid solubility and LBF viability, but precludes enduring effects on receptor promiscuity and off target toxicity. Finally, recent efforts to generate solid LBF are briefly described as a means to circumvent the need to encapsulate in soft or hard gelatin capsules, although the latter remain popular with consumers and a proven means of LBF delivery.

Development and validation of bioanalytical UHPLC-UV method for simultaneous analysis of unchanged fenofibrate and its metabolite fenofibric acid in rat plasma: Application to pharmacokinetics

A simple, precise, selective and fast ultra-high performance liquid chromatography (UHPLC-UV) method has been developed and validated for the simultaneous determination of a lipid regulating agent fenofibrate and its metabolite fenofibric acid in rat plasma. The chromatographic separation was carried out on a reversed-phase Acquity® BEH C₁₈ column using methanol–water (65:35, v/v) as the mobile phase. The isocratic flow was 0.3 ml/min with rapid run time of 2.5 min and UV detection was at 284 nm. The method was validated over a concentration range of 100–10000 ng/ml (r² ⩾ 0.9993). The selectivity, specificity, recovery, accuracy and precision were validated for determination of fenofibrate/fenofibric acid in rat plasma. The lower limits of detection and quantitation of the method were 30 and 90 ng/ml for fenofibrate and 40 and 100 ng/ml for fenofibric acid, respectively. The within and between-day coefficients of variation were less than 5%. The validated method has been successfully applied to measure the plasma concentrations in pharmacokinetics study of fenofibrate in an animal model to illustrate the scope and application of the method.

Physiologically Based Pharmacokinetic (PBPK) Modeling and Simulation Approaches: A Systematic Review of Published Models, Applications, and Model Verification

Modeling and simulation of drug disposition has emerged as an important tool in drug development, clinical study design and regulatory review, and the number of physiologically based pharmacokinetic (PBPK) modeling related publications and regulatory submissions have risen dramatically in recent years. However, the extent of use of PBPK modeling by researchers, and the public availability of models has not been systematically evaluated. This review evaluates PBPK-related publications to 1) identify the common applications of PBPK modeling; 2) determine ways in which models are developed; 3) establish how model quality is assessed; and 4) provide a list of publically available PBPK models for sensitive P450 and transporter substrates as well as selective inhibitors and inducers. PubMed searches were conducted using the terms "PBPK" and "physiologically based pharmacokinetic model" to collect published models. Only papers on PBPK modeling of pharmaceutical agents in humans published in English between 2008 and May 2015 were reviewed. A total of 366 PBPK-related articles met the search criteria, with the number of articles published per year rising steadily. Published models were most commonly used for drug-drug interaction predictions (28%), followed by interindividual variability and general clinical pharmacokinetic predictions (23%), formulation or absorption modeling (12%), and predicting age-related changes in pharmacokinetics and disposition (10%). In total, 106 models of sensitive substrates, inhibitors, and inducers were identified. An in-depth analysis of the model development and verification revealed a lack of consistency in model development and quality assessment practices, demonstrating a need for development of best-practice guidelines.

Development of omega-3 phospholipid-based solid dispersion of fenofibrate for the enhancement of oral bioavailability

This research aimed to develop the omega-3 phospholipids based solid dispersion to improve the oral bioavailability of fenofibrate. The omega-3 phospholipids based solid dispersion formulation (OPSD) was prepared by an antisolvent precipitation with immediate freeze-drying and the optimal composition of the formulation was determined as the ratios of sucrose to krill oil of 5:1 (w/w), krill oil to fenofibrate of 1.5:1 (w/w), and antisolvent to solvent of 6:4 (v/v). The developed OPSD formulation was characterized by using scanning electron microscopy (SEM), X-ray powder diffraction (XRPD), and differential scanning calorimetry (DSC), which indicated the crystalline state of fenofibrate in the OPSD. The drug release profiles were also examined at different pHs. The OPSD achieved almost complete dissolution within 15 min, while the untreated powder and physical mixture exhibited minimal dissolution (less than 10% even after 2h). Furthermore, this formulation effectively increased the oral drug exposure in rats, as the Cmax and AUC of fenofibric acid (an active metabolite) were enhanced by approximately 6-7 folds. These results suggest that the OPSD formulation should be promising for improving the oral bioavailability of fenofibrate.

Prediction of in-vivo pharmacokinetic profile for immediate and modified release oral dosage forms of furosemide using an in-vitro-in-silico-in-vivo approach

OBJECTIVES

To develop a physiologically based pharmacokinetic (PBPK) model for furosemide immediate release (IR) tablets and modified release (MR) capsules by coupling biorelevant dissolution testing results with pharmacokinetic (PK) and physiologic parameters, and to investigate the key factors influencing furosemide absorption using simulation approaches and the PBPK model.

METHODS

Using solubility, dissolution kinetics, gastrointestinal (GI) parameters and disposition parameters, a PBPK model for furosemide was developed with STELLA software. Solubility and dissolution profiles for both formulations were evaluated in biorelevant and compendial media. The simulated plasma profiles were compared with in-vivo profiles using point estimates of area under plasma concentration-time curve, maximal concentration after the dose and time to maximal concentration after the dose.

KEY FINDINGS

Simulated plasma profiles of both furosemide IR tablets and MR capsules were similar to the observed in-vivo profile in terms of PK parameters. Sensitivity analysis of the IR tablet model indicated that both the gastric emptying and absorption rate have an influence on the plasma profile. For the MR capsules, the sensitivity analysis suggested that the release rate in the small intestine, gastric emptying and the absorption rate all have an influence on the plasma profile.

CONCLUSIONS

A predictive model to describe both IR and MR dosage forms containing furosemide was attained. Because sensitivity analysis of the model is able to identify key factors influencing the plasma profile, this in-vitro-in-silico-in-vivo approach could be a useful tool for facilitating formulation development of drug products.

Pharmacokinetic aspects and in vitro-in vivo correlation potential for lipid-based formulations

Lipid-based formulations have been an attractive choice among novel drug delivery systems for enhancing the solubility and bioavailability of poorly soluble drugs due to their ability to keep the drug in solubilized state in the gastrointestinal tract. These formulations offer multiple advantages such as reduction in food effect and inter-individual variability, ease of preparation, and the possibility of manufacturing using common excipients available in the market. Despite these advantages, very few products are available in the present market, perhaps due to limited knowledge in the in vitro tests (for prediction of in vivo fate) and lack of understanding of the mechanisms behind pharmacokinetic and biopharmaceutical aspects of lipid formulations after oral administration. The current review aims to provide a detailed understanding of the in vivo processing steps involved after oral administration of lipid formulations, their pharmacokinetic aspects and in vitro in vivo correlation (IVIVC) perspectives. Various pharmacokinetic and biopharmaceutical aspects such as formulation dispersion and lipid digestion, bioavailability enhancement mechanisms, impact of excipients on efflux transporters, and lymphatic transport are discussed with examples. In addition, various IVIVC approaches towards predicting in vivo data from in vitro dispersion/precipitation, in vitro lipolysis and ex vivo permeation studies are also discussed in detail with help of case studies.

The role of lipid-based nano delivery systems on oral bioavailability enhancement of fenofibrate, a BCS II drug: comparison with fast-release formulations

The aim of this study was to compare various formulations solid dispersion pellets (SDP), nanostructured lipid carriers (NLCs) and a self-microemulsifying drug delivery system (SMEDDS) generally accepted to be the most efficient drug delivery systems for BCS II drugs using fenofibrate (FNB) as a model drug. The size and morphology of NLCs and SMEDDS was characterized by dynamic light scattering (DLS) and transmission electron microscopy (TEM). Their release behaviors were investigated in medium with or without pancreatic lipase. The oral bioavailability of the various formulations was compared in beagle dogs using commercial Lipanthyl® capsules (micronized formulation) as a reference. The release of FNB from SDP was much faster than that from NLCs and SMEDDS in medium without lipase, whereas the release rate from NLCs and SMEDDS was increased after adding pancreatic lipase into the release medium. However, NLCs and SMEDDS increased the bioavailability of FNB to 705.11% and 809.10%, respectively, in comparison with Lipanthyl® capsules, although the relative bioavailability of FNB was only 366.05% after administration of SDPs. Thus, lipid-based drug delivery systems (such as NLCs and SMEDDS) may have more advantages than immediate release systems (such as SDPs and Lipanthyl® capsules).

Biopharmaceutical modeling of drug supersaturation during lipid-based formulation digestion considering an absorption sink

PURPOSE

In vitro lipolysis is widely utilized for predicting in vivo performance of oral lipid-based formulations (LBFs). However, evaluation of LBFs in the absence of an absorption sink may have limited in vivo relevance. This study aimed at employing biopharmaceutical modeling to simulate LBF digestion and drug supersaturation in a continuous absorptive environment.

METHODS

Three fenofibrate-loaded LBFs were characterized in vitro (dispersion and lipolysis) and drug precipitation was monitored using in-line Raman spectroscopy. In vitro data were combined with pharmacokinetic data derived from an in vivo study in pigs to simulate intestinal LBF transit. This biopharmaceutical model allowed calculation of lipolysis-triggered drug supersaturation while drug and lipolysis products are absorbed from the intestine.

RESULTS

The biopharmaceutical model predicted that, in a continuous absorption environment, fenofibrate supersaturation was considerably lower compared to in vitro lipolysis (non-sink). Hence, the extensive drug precipitation observed in vitro was predicted to be unlikely in vivo. The absorption of lipolysis products increased drug supersaturation, but drug precipitation was unlikely for highly permeable drugs.

CONCLUSIONS

Biopharmaceutical modeling is a valuable approach for predicting LBFs performance in vivo. In the absence of in vitro tools simulating absorptive conditions, modeling strategies should be further considered.

In vitro lipolysis data does not adequately predict the in vivo performance of lipid-based drug delivery systems containing fenofibrate

The present study investigated the utility of in vitro lipolysis performance indicators drug solubilization and maximum supersaturation ratio (SR(M)) for their predictive use for the in vivo performance in a minipig model. The commercial Lipanthyl formulation and a series of LbDDS based on identical self-nanoemulsifying drug delivery systems (SNEDDS) containing 200 mg of fenofibrate, either dissolved or suspended, were subjected to combined gastric (pH 2) and intestinal (pH 6.5) in vitro lipolysis. Based on the solubilization profiles and SRM the rank-order SNEDDS (75% drug load) > super-SNEDDS (150% drug load, dissolved) = SNEDDS suspension (150% drug load, partially suspended) > Lipanthyl was established, with an increased likelihood of drug precipitation above SR(M) > 3. The in vitro performance, however, was not reproduced in vivo in a minipig model as the mean plasma concentration over time curves of all LbDDS were comparable, independent of the initial physical state of the drug. There was no correlation between the area under the solubilization-time curves (AUC(in vitro)) of the intestinal step and the AUC(in vivo). The study suggests careful interpretation of in vitro performance criteria and revision of LbDDS optimization towards increased solubilization.

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

The Biopharmaceutics Classification System (BCS) has found widespread utility in drug discovery, product development and drug product regulatory sciences. The classification scheme captures the two most significant factors influencing oral drug absorption; solubility and intestinal permeability and it has proven to be a very useful and a widely accepted starting point for drug product development and drug product regulation. The mechanistic base of the BCS approach has, no doubt, contributed to its wide spread acceptance and utility. Nevertheless, underneath the simplicity of BCS are many detailed complexities, both in vitro and in vivo which must be evaluated and investigated for any given drug and drug product. In this manuscript we propose a simple extension of the BCS classes to include sub-specification of acid (a), base (b) and neutral (c) for classes II and IV. Sub-classification for Classes I and III (high solubility drugs as currently defined) is generally not needed except perhaps in border line solubility cases. It is well known that the , pKa physical property of a drug (API) has a significant impact on the aqueous solubility dissolution of drug from the drug product both in vitro and in vivo for BCS Class II and IV acids and bases, and is the basis, we propose for a sub-classification extension of the original BCS classification. This BCS sub-classification is particularly important for in vivo predictive dissolution methodology development due to the complex and variable in vivo environment in the gastrointestinal tract, with its changing pH, buffer capacity, luminal volume, surfactant luminal conditions, permeability profile along the gastrointestinal tract and variable transit and fasted and fed states. We believe this sub-classification is a step toward developing a more science-based mechanistic in vivo predictive dissolution (IPD) methodology. Such a dissolution methodology can be used by development scientists to assess the likelihood of a formulation and dosage form functioning as desired in humans, can be optimized along with parallel human pharmacokinetic studies to set a dissolution methodology for Quality by Design (QbD) and in vitro-in vivo correlations (IVIVC) and ultimately can be used as a basis for a dissolution standard that will ensure continued in vivo product performance.

Comparison of in vitro tests at various levels of complexity for the prediction of in vivo performance of lipid-based formulations: case studies with fenofibrate

The objectives of this study were to characterise three prototype fenofibrate lipid-based formulations using a range of in vitro tests with differing levels of complexity and to assess the extent to which these methods provide additional insight into in vivo findings. Three self-emulsifying drug delivery systems (SEDDS) were prepared: a long chain (LC) Type IIIA SEDDS, a medium chain (MC) Type IIIA SEDDS, and a Type IIIB/IV SEDDS containing surfactants only (SO). Dilution, dispersion and digestion tests were performed to assess solubilisation and precipitation behaviour in vitro. Focussed beam reflectance measurements and solid state characterisation of the precipitate was conducted. Oral bioavailability was evaluated in landrace pigs. Dilution and dispersion testing revealed that all three formulations were similar in terms of maintaining fenofibrate in a solubilised state on dispersion in biorelevant media. During in vitro digestion, the Type IIIA formulations displayed limited drug precipitation (<5%), whereas the Type IIIB/IV formulation displayed extensive drug precipitation (~70% dose). Solid state analysis confirmed that precipitated fenofibrate was crystalline. The oral bioavailability was similar for the three lipid formulations (65-72%). In summary, the use of LC versus MC triglycerides in Type IIIA SEDDS had no impact on the bioavailability of fenofibrate. The extensive precipitation observed with the Type IIIB/IV formulation during in vitro digestion did not adversely impact fenofibrate bioavailability in vivo, relative to the Type IIIA formulations. These results were predicted suitably using in vitro dilution and dispersion testing, whereas the in vitro digestion method failed to predict the outcome of the in vivo study.

PBPK models for the prediction of in vivo performance of oral dosage forms

Drug absorption from the gastrointestinal (GI) tract is a highly complex process dependent upon numerous factors including the physicochemical properties of the drug, characteristics of the formulation and interplay with the underlying physiological properties of the GI tract. The ability to accurately predict oral drug absorption during drug product development is becoming more relevant given the current challenges facing the pharmaceutical industry. Physiologically-based pharmacokinetic (PBPK) modeling provides an approach that enables the plasma concentration-time profiles to be predicted from preclinical in vitro and in vivo data and can thus provide a valuable resource to support decisions at various stages of the drug development process. Whilst there have been quite a few successes with PBPK models identifying key issues in the development of new drugs in vivo, there are still many aspects that need to be addressed in order to maximize the utility of the PBPK models to predict drug absorption, including improving our understanding of conditions in the lower small intestine and colon, taking the influence of disease on GI physiology into account and further exploring the reasons behind population variability. Importantly, there is also a need to create more appropriate in vitro models for testing dosage form performance and to streamline data input from these into the PBPK models. As part of the Oral Biopharmaceutical Tools (OrBiTo) project, this review provides a summary of the current status of PBPK models available. The current challenges in PBPK set-ups for oral drug absorption including the composition of GI luminal contents, transit and hydrodynamics, permeability and intestinal wall metabolism are discussed in detail. Further, the challenges regarding the appropriate integration of results from in vitro models, such as consideration of appropriate integration/estimation of solubility and the complexity of the in vitro release and precipitation data, are also highlighted as important steps to advancing the application of PBPK models in drug development. It is expected that the "innovative" integration of in vitro data from more appropriate in vitro models and the enhancement of the GI physiology component of PBPK models, arising from the OrBiTo project, will lead to a significant enhancement in the ability of PBPK models to successfully predict oral drug absorption and advance their role in preclinical and clinical development, as well as for regulatory applications.