The Potential for Drug Supersaturation during Intestinal Processing of Lipid-Based Formulations May Be Enhanced for Basic Drugs

Predictions of biorelevant solubility change during dispersion and digestion of lipid-based formulations

Computational approaches are increasingly explored in development of drug products, including the development of lipid-based formulations (LBFs), to assess their feasibility for achieving adequate oral absorption at an early stage. This study investigated the use of computational pharmaceutics approaches to predict solubility changes of poorly soluble drugs during dispersion and digestion in biorelevant media. Concentrations of 30 poorly water-soluble drugs were determined pre- and post-digestion with in-line UV probes using the MicroDISS Profiler™. Generally, cationic drugs displayed higher drug concentrations post-digestion, whereas for non-ionized drugs there was no discernible trend between drug concentration in dispersed and digested phase. In the case of anionic drugs there tended to be a decrease or no change in the drug concentration post-digestion. Partial least squares modelling was used to identify the molecular descriptors and drug properties which predict changes in solubility ratio in long-chain LBF pre-digestion (R2 of calibration = 0.80, Q2 of validation = 0.64) and post-digestion (R2 of calibration = 0.76, Q2 of validation = 0.72). Furthermore, multiple linear regression equations were developed to facilitate prediction of the solubility ratio pre- and post-digestion. Applying three molecular descriptors (melting point, LogD, and number of aromatic rings) these equations showed good predictivity (pre-digestion R2 = 0.70, and post-digestion R2 = 0.68). The model developed will support a computationally guided LBF strategy for emerging poorly water-soluble drugs by predicting biorelevant solubility changes during dispersion and digestion. This facilitates a more data-informed developability decision making and subsequently facilitates a more efficient use of formulation screening resources.

Assessment of in Vivo Performance of Lipid-Based Formulations: Correlation between in Vitro Drug Release Profiles and in Vivo Absorption Rate Profiles

The purpose of this study was to assess the in vivo absorption enhancement effects of lipid-based formulations (LBFs) through in vitro release studies. The type IIIA-MC (medium-chain) and type IIIA-LC (long-chain) formulations containing a Biopharmaceutics Classification System (BCS) Class II drug (dipyridamole or ketoconazole) were used as model LBFs. The type IIIA-MC formulation, but not the type IIIA-LC formulation, showed a higher initial absorption rate than the control suspension for both model drugs in rats. An in vitro side-by-side chamber system coupled with a lipid digestion model was used to measure free drugs, available for intestinal absorption, that are released from a model LBF. The profiles of free drug concentration on the donor side were determined by calculating the ratio of permeation rate (LBF/suspension) at every sampling interval. The in vitro free drug concentration was immediately supersaturated when the digestion of type IIIA-MC formulation was initiated for both drugs, which would cause the initially high absorption rate in rats. In contrast, the free concentration of the type IIIA-LC formulation became lower than the equilibrium solubility over time for both drugs. Overall, the profiles of in vitro free concentrations were consistent with those of in vivo absorption rates for both drugs and all LBFs. These findings would help predict the in vivo performance and establish an in vitro-in vivo correlation (IVIVC) of LBFs.

[Elucidation and Prediction of Absorption Behavior After Oral Administration of Poorly Water-Soluble Drugs as Different Lipid-Based Formulations]

Lipid-based formulations (LBFs) are isotropic mixtures typically comprising lipids, surfactants, and/or co-solvents, in which drugs are pre-solubilized. After oral administration, LBFs are piggybacked into endogenous lipid digestion pathways. This triggers drug super-saturation and improves absorption. However, super-saturation poses a risk of drug precipitation, which generally leads to poor drug absorption. Furthermore, a series of aqueous colloidal species including digestion products (typically fatty acids and monoglycerides) and endogenous molecules (bile acids and phospholipids) increase the drug solubilization capacity of the intestinal fluid (compared with that of the normal intestinal fluid). However, the solubilization/precipitation behavior may change according to the LBF composition (e.g., the drug loading amount and type of formulation excipients), which may ultimately lead to differences in oral absorption. This review summarizes the results of the evaluation and prediction of the effect of LBFs composition on oral absorption and provides an in-depth understanding of the drug absorption mechanisms when using LBFs.

Mechanisms and Extent of Enhanced Passive Permeation by Colloidal Drug Particles

Formulations containing nanosized drug particles such as nanocrystals and nanosized amorphous drug aggregates recently came into light as promising strategies to improve the bioavailability of poorly soluble drugs. However, the increased solubility due to the reduction in particle size cannot adequately explain the enhanced bioavailability. In this study, the mechanisms and extent of enhanced passive permeation by drug particles were investigated using atazanavir, lopinavir, and clotrimazole as model drugs. Franz diffusion cells with lipid-infused membranes were utilized to evaluate transmembrane flux. The impact of stirring rate, receiver buffer condition, and particle size was investigated, and mass transport analyses were conducted to calculate transmembrane flux. Flux enhancement by particles was found to be dependent on particle size as well as the partitioning behavior of the drug between the receiver solution and the membrane, which is determined by both the drug and buffer used. A flux plateau was observed at high particle concentrations above amorphous solubility, confirming that mass transfer of amorphous drug particles from the aqueous solution to the membrane occurs only through the molecularly dissolved drug. Mass transport models were used to calculate flux enhancement by particles for various drugs at different conditions. Good agreements were obtained between experimental and predicted values. These results should contribute to improved bioavailability prediction of nanosized drug particles and better design of formulations containing colloidal drug particles.

The impact of quantity of lipid based formulations with different compositions on the oral absorption of ritonavir: A trade-off between apparent solubility and permeability

In this study, the effect of the quantity of lipid-based formulations (LBFs) on the oral absorption of ritonavir (RTV), a model for poorly water-soluble drugs, was investigated. Two types of LBFs, comprising short- and medium-chain lipids (LBF-SMC) and long-chain lipids (LBF-LC) loaded with different masses of RTV, were prepared. Then, the respective LBFs were dispersed in distilled water at concentrations of 1.0, 2.0, and 3.0% w/w, which provided the same drug concentration for all formulations. When 1.0% LBF-SMC and LBF-LC were orally administered to rats, the oral absorption was significantly improved compared with that of the suspension (a reference formulation) because of enhanced solubilization of RTV in the gastrointestinal tract; however, this improvement was lower for LBF-LC than for LBF-SMC. The oral absorption decreased with increasing LBF concentration for both LBF-SMC and LBF-LC. The in vitro permeation in sequence with in vitro digestion revealed that this phenomenon was caused by a reduction in the free drug concentration in the gastrointestinal tract. Moreover, the effect of decreasing the free concentration was more remarkable for LBF-LC than for LBF-SMC because of the greater solubilization capacity of LC digestion products. These findings may be useful for designing improved drug delivery systems.

Best practices in current models mimicking drug permeability in the gastrointestinal tract - an UNGAP review

The absorption of orally administered drug products is a complex, dynamic process, dependent on a range of biopharmaceutical properties; notably the aqueous solubility of a molecule, stability within the gastrointestinal tract (GIT) and permeability. From a regulatory perspective, the concept of high intestinal permeability is intrinsically linked to the fraction of the oral dose absorbed. The relationship between permeability and the extent of absorption means that experimental models of permeability have regularly been used as a surrogate measure to estimate the fraction absorbed. Accurate assessment of a molecule's intestinal permeability is of critical importance during the pharmaceutical development process of oral drug products, and the current review provides a critique of in vivo, in vitro and ex vivo approaches. The usefulness of in silico models to predict drug permeability is also discussed and an overview of solvent systems used in permeability assessments is provided. Studies of drug absorption in humans are an indirect indicator of intestinal permeability, but in vitro and ex vivo tools provide initial screening approaches are important tools for direct assessment of permeability in drug development. Continued refinement of the accuracy of in silico approaches and their validation with human in vivo data will facilitate more efficient characterisation of permeability earlier in the drug development process and will provide useful inputs for integrated, end-to-end absorption modelling.

Effects of Lipid Digestion and Drug Permeation/Re-Dissolution on Absorption of Orally Administered Ritonavir as Different Lipid-Based Formulations

The aim of this study is to clarify absorption mechanisms after oral administration of ritonavir (RTV) from different types of lipid-based formulations (LBFs) with particular emphasis on the effect of lipid digestion and drug permeation/re-dissolution on the oral absorption. Four LBFs were prepared; three contained either long-chain (LC) or medium-chain (MC) lipids [lipid formulation classification system (LFCS) Type II-LC, Type IIIA-MC, and Type IIIB-MC] and the fourth contained only surfactant and co-solvent (Type IV). The solubility of RTV in those LBFs was determined and drug subsequently loaded at 85% w/w of the saturated solubility in the formulations. Then, each LBF containing drug was added into a model rat intestinal fluid at approximately 2.5% w/v for evaluation using an in vitro digestion model. In vitro digestion study showed the ability of Type II-LC and Type IIIA-MC to support continued solubilization of RTV, and moderate supersaturation was observed in Type IIIA-MC. In contrast, RTV partly precipitated in the Type IIIB-MC during digestion, and the Type IV formulation lost its solubilization capacity rapidly upon dispersion, leading to drastic precipitation. Oral administration of RTV as Type IIIA-MC to rats showed significantly higher area under the plasma concentration-time curve compared to control suspension, whereas it was not improved with Type II-LC administration despite complete solubilization of RTV during digestion. From the results of in vitro permeation across dialysis membrane (a molecular weight cutoff of > 1000 Da), this may be attributed to the lowered free concentration in the gastrointestinal tract owing to incorporation of RTV into the undigested LC lipid. Oral absorption drastically increased with Type IIIB-MC and Type IV despite the observed moderate and drastic precipitation, respectively. Powder X-ray diffraction analysis revealed that the precipitate was amorphous. Therefore, improved re-solubilization may partly contribute to improved absorption. The present study revealed detailed absorption mechanisms from LBFs with different compositions. Our findings may be useful for selecting appropriate excipients to design optimal LBFs for poorly water-soluble drugs.

Physiologically Based Pharmacokinetic/Pharmacodynamic Modeling to Support Waivers of In Vivo Clinical Studies: Current Status, Challenges, and Opportunities

Physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) modeling has been extensively applied to quantitatively translate in vitro data, predict the in vivo performance, and ultimately support waivers of in vivo clinical studies. In the area of biopharmaceutics and within the context of model-informed drug discovery and development (MID3), there is a rapidly growing interest in applying verified and validated mechanistic PBPK models to waive in vivo clinical studies. However, the regulatory acceptance of PBPK analyses for biopharmaceutics and oral drug absorption applications, which is also referred to variously as "PBPK absorption modeling" [Zhang et al. CPT: Pharmacometrics Syst. Pharmacol. 2017, 6, 492], "physiologically based absorption modeling", or "physiologically based biopharmaceutics modeling" (PBBM), remains rather low [Kesisoglou et al. J. Pharm. Sci. 2016, 105, 2723] [Heimbach et al. AAPS J. 2019, 21, 29]. Despite considerable progress in the understanding of gastrointestinal (GI) physiology, in vitro biopharmaceutic and in silico tools, PBPK models for oral absorption often suffer from an incomplete understanding of the physiology, overparameterization, and insufficient model validation and/or platform verification, all of which can represent limitations to their translatability and predictive performance. The complex interactions of drug substances and (bioenabling) formulations with the highly dynamic and heterogeneous environment of the GI tract in different age, ethnic, and genetic groups as well as disease states have not been yet fully elucidated, and they deserve further research. Along with advancements in the understanding of GI physiology and refinement of current or development of fully mechanistic in silico tools, we strongly believe that harmonization, interdisciplinary interaction, and enhancement of the translational link between in vitro, in silico, and in vivo will determine the future of PBBM. This Perspective provides an overview of the current status of PBBM, reflects on challenges and knowledge gaps, and discusses future opportunities around PBPK/PD models for oral absorption of small and large molecules to waive in vivo clinical studies.

The Solubility-Permeability Interplay for Solubility-Enabling Oral Formulations

The Biopharmaceutical classification system (BCS) classifies the drugs based on their intrinsic solubility and intestinal permeability. The drugs with good solubility and intestinal permeability have good bioavailability. The drugs with poor solubility and poor permeability have solubility dependent and permeability dependent bioavailability, respectively. In the current pharmaceutical field, most of the drugs have poor solubility. To solve the problem of poor solubility, various solubility enhancement approaches have been successfully used. The effects of these solubility enhancing approaches on the intestinal permeability of the drugs are a matter of concern, and must not be overlooked. The current review article focuses on the effect of various solubility enhancing approaches viz. cyclodextrin, surfactant, cosolvent, hydrotropes, and amorphous solid dispersion, on the intestinal permeability of drugs. This article will help in the designing of the optimized formulations having balanced solubility enhancement without affecting the permeability of drugs.

Effect of lipids on absorption of carvedilol in dogs: Is coadministration of lipids as efficient as a lipid-based formulation?

Lipid-based formulations (LBFs) is a formulation strategy for enabling oral delivery of poorly water-soluble drugs. However, current use of this strategy is limited to a few percent of the marketed products. Reasons for that are linked to the complexity of LBFs, chemical instability of pre-dissolved drug and a limited understanding of the influence of LBF intestinal digestion on drug absorption. The aim of this study was to explore intestinal drug solubilization from a long-chain LBF, and evaluate whether coadministration of LBF is as efficient as a lipid-based drug formulation containing the pre-dissolved model drug carvedilol. Thus, solubility studies of this weak base were performed in simulated intestinal fluid (SIF) and aspirated dog intestinal fluid (DIF). DIF was collected from duodenal stomas after dosing of water and two levels (1 g and 2 g) of LBF. Similarly, the in vitro SIF solubility studies were conducted prior to, and after addition of, undigested or digested LBF. The DIF fluid was further characterized for lipid digestion products (free fatty acids) and bile salts. Subsequently, carvedilol was orally administered to dogs in a lipid-based drug formulation and coadministered with LBF, and drug plasma exposure was assessed. In addition to these studies, in vitro drug absorption from the different formulation approaches were evaluated in a lipolysis-permeation device, and the obtained data was used to evaluate the in vitro in vivo correlation. The results showed elevated concentrations of free fatty acids and bile salts in the DIF when 2 g of LBF was administered, compared to only water. As expected, the SIF and DIF solubility data revealed that carvedilol solubilization increased by the presence of lipids and lipid digestion products. Moreover, coadministration of LBF and drug demonstrated equal plasma exposure to the lipid-based drug formulation. Furthermore, evaluation of in vitro absorption resulted in the same rank order for the LBFs as in the in vivo dog study. In conclusion, this study demonstrated increased intestinal solubilization from a small amount of LBF, caused by lipid digestion products and bile secretion. The outcomes also support the use of coadministration of LBF as a potential dosing regimen in cases where it is beneficial to have the drug in the solid form, e.g. due to chemical instability in the lipid vehicle. Finally, the in vitro lipolysis-permeation used herein established IVIVC for carvedilol in the presence of LBFs.

Colloidal aspects of dispersion and digestion of self-dispersing lipid-based formulations for poorly water-soluble drugs

Self-dispersing lipid-based formulations, particularly self-microemulsifying drug delivery systems (SMEDDS) have gained an increased interest in recent times as a means to enhance the oral bioavailability of poorly water-soluble lipophilic drugs. Upon dilution, SMEDDS self-emulsify in an aqueous fluid and usually form a kinetically stable oil-in-water emulsion or in some rare cases a true thermodynamically stable microemulsion. The digestion of the formulation leads to the production of amphiphilic digestion products that interact with endogenous amphiphilic components and form self-assembled colloidal phases in the aqueous environment of the intestine. The formed colloidal phases play a pivotal role in maintaining the lipophilic drug in the solubilised state during gastrointestinal transit prior to absorption. Thus, this review describes the structural characterisation techniques employed for SMEDDS and the recent literature studies that elucidated the colloidal aspects during dispersion and digestion of SMEDDS and solid SMEDDS. Possible future studies are proposed to gain better understanding on the colloidal aspects of SMEDDS and solid SMEDDS.

The impact of digestion is essential to the understanding of milk as a drug delivery system for poorly water soluble drugs

Milk has previously been considered as a potential lipid-based drug delivery system for poorly water soluble drugs but it has never gained significant attention. This is in part because relying on solubility in lipid-based formulations (in this case milk) does not provide a complete picture of the behavior of such systems upon digestion. Herein, we demonstrate using time resolved X-ray scattering that the digestion of milk is actually crucial to the solubilisation of a poorly water-soluble drug, halofantrine. Halofantrine was chosen because its behaviour in lipid-based formulations has been widely investigated and because of its close structural relationship to lumefantrine, an antimalarial drug of current interest for the treatment of paediatric malaria. The transformation of the drug from a crystalline solid form in suspension in milk, to a solubilised form as a direct consequence of lipolysis highlights that consideration of digestion of the milk lipids as a critical process that influences drug solubilisation and availability for absorption is vital.

Impact of Drug Physicochemical Properties on Lipolysis-Triggered Drug Supersaturation and Precipitation from Lipid-Based Formulations

In this study we investigated lipolysis-triggered supersaturation and precipitation of a set of model compounds formulated in lipid-based formulations (LBFs). The purpose was to explore the relationship between precipitated solid form and inherent physicochemical properties of the drug. Eight drugs were studied after formulation in three LBFs, representing lipid-rich (extensively digestible) to surfactant-rich (less digestible) formulations. In vitro lipolysis of drug-loaded LBFs were conducted, and the amount of dissolved and precipitated drug was quantified. Solid form of the precipitated drug was characterized with polarized light microscopy (PLM) and Raman spectroscopy. A significant solubility increase for the weak bases in the presence of digestion products was observed, in contrast to the neutral and acidic compounds for which the solubility decreased. The fold-increase in solubility was linked to the degree of ionization of the weak bases and thus their attraction to free fatty acids. A high level of supersaturation was needed to cause precipitation. For the weak bases, the dose number indicated that precipitation would not occur during lipolysis; hence, these compounds were not included in further studies. The solid state analysis proved that danazol and griseofulvin precipitated in a crystalline form, while niclosamide precipitated as a hydrate. Felodipine and indomethacin crystals were visible in the PLM, whereas the Raman spectra showed presence of amorphous drug, indicating amorphous precipitation that quickly crystallized. The solid state analysis was combined with literature data to allow analysis of the relationship between solid form and the physicochemical properties of the drug. It was found that low molecular weight and high melting temperature increases the probability of crystalline precipitation, whereas precipitation in an amorphous form was favored by high molecular weight, low melting temperature, and positive charge.

The solubility-permeability interplay and oral drug formulation design: Two heads are better than one

Poor aqueous solubility is a major challenge in today's biopharmaceutics. While solubility-enabling formulations can significantly increase the apparent solubility of the drug, the concomitant effect on the drug's apparent permeability has been largely overlooked. The mathematical equation to describe the membrane permeability of a drug comprises the membrane/aqueous partition coefficient, which in turn is dependent on the drug's apparent solubility in the GI milieu, suggesting that the solubility and the permeability are closely related, exhibit a certain interplay between them, and treating the one irrespectively of the other may be insufficient. In this article, an overview of this solubility-permeability interplay is provided, and the available data is analyzed in the context of the effort to maximize the overall drug exposure. Overall, depending on the type of solubility-permeability interplay, the permeability may decrease, remain unchanged, and even increase, in a way that may critically affect the formulation capability to improve the overall absorption. Therefore, an intelligent design of solubility-enabling formulation needs to consider both the solubility afforded by the formulation and the permeability in the new luminal environment resulting from the formulation.

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.

A new in vitro lipid digestion - in vivo absorption model to evaluate the mechanisms of drug absorption from lipid-based formulations

PURPOSE

In vitro lipid digestion models are commonly used to screen lipid-based formulations (LBF), but in vitro-in vivo correlations are in some cases unsuccessful. Here we enhance the scope of the lipid digestion test by incorporating an absorption 'sink' into the experimental model.

METHODS

An in vitro model of lipid digestion was coupled directly to a single pass in situ intestinal perfusion experiment in an anaesthetised rat. The model allowed simultaneous real-time analysis of the digestion and absorption of LBFs of fenofibrate and was employed to evaluate the influence of formulation digestion, supersaturation and precipitation on drug absorption.

RESULTS

Formulations containing higher quantities of co-solvent and surfactant resulted in higher supersaturation and more rapid drug precipitation in vitro when compared to those containing higher quantities of lipid. In contrast, when the same formulations were examined using the coupled in vitro lipid digestion - in vivo absorption model, drug flux into the mesenteric vein was similar regardless of in vitro formulation performance.

CONCLUSION

For some drugs, simple in vitro lipid digestion models may underestimate the potential for absorption from LBFs. Consistent with recent in vivo studies, drug absorption for rapidly absorbed drugs such as fenofibrate may occur even when drug precipitation is apparent during in vitro digestion.

In situ perfusion in rodents to explore intestinal drug absorption: challenges and opportunities

The in situ intestinal perfusion technique in rodents is a very important absorption model, not only because of its predictive value, but it is also very suitable to unravel the mechanisms underlying intestinal drug absorption. This literature overview covers a number of specific applications for which the in situ intestinal perfusion set-up can be applied in favor of established in vitro absorption tools, such as the Caco-2 cell model. Qualities including the expression of drug transporters and metabolizing enzymes relevant for human intestinal absorption and compatibility with complex solvent systems render the in situ technique the most designated absorption model to perform transporter-metabolism studies or to evaluate the intestinal absorption from biorelevant media. Over the years, the in situ intestinal perfusion model has exhibited an exceptional ability to adapt to the latest challenges in drug absorption profiling. For instance, the introduction of the mesenteric vein cannulation allows determining the appearance of compounds in the blood and is of great use, especially when evaluating the absorption of compounds undergoing intestinal metabolism. Moreover, the use of the closed loop intestinal perfusion set-up is interesting when compounds or perfusion media are scarce. Compatibility with emerging trends in pharmaceutical profiling, such as the use of knockout or transgenic animals, generates unparalleled possibilities to gain mechanistic insight into specific absorption processes. Notwithstanding the fact that the in situ experiments are technically challenging and relatively time-consuming, the model offers great opportunities to gain insight into the processes determining intestinal drug absorption.

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.