In-vitro permeability screening of melt extrudate formulations containing poorly water-soluble drug compounds using the phospholipid vesicle-based barrier

Development of a novel human stratum corneum mimetic phospholipid -vesicle-based permeation assay models for in vitro permeation studies

OBJECTIVES

To develop and evaluate a novel human stratum corneum (SC) mimetic phospholipid vesicle-based permeation assay (PVPASC) model for in vitro permeation studies.

SIGNIFICANCE

Due to the increasing restrictions on the use of human and animal skins, artificial skin models have attracted substantial interest in pharmaceuticals and cosmetic industries. In this study, a modified PVPASC model containing both SC lipids and proteins was developed.

METHODS

The PVPASC model was optimized by altering the lipid composition and adding keratin in the formulation of large liposomes. The barrier properties were monitored by measuring the electrical resistance (ER) and permeability of Rhodamine B (RB). The modified PVPASC model was characterized in terms of the surface topography, solvent influence and storage stability. The permeation studies of the active components in Compound Nanxing Zhitong Plaster (CNZP) were performed to examine the capability of PVPASC in the application of skin penetration.

RESULTS

The ER and Papp values of RB obtained from the optimized PVPASC model indicated a similar barrier property to porcine ear skin. Scanning electron microscope analysis demonstrated a mimic 'brick-and-mortar' structure. The PVPASC model can be stored for three weeks at -20 °C, and withstand the presence of different receptor medium for 24 h. The permeation studies of the active components demonstrated a good correlation (r2 = 0.9136) of Papp values between the drugs' permeation through the PVPASC model and porcine ear skin.

CONCLUSION

Keratin contained composite phospholipid vesicle-based permeation assay models have been proven to be potential skin tools in topical/transdermal permeation studies.

Overcoming drug impurity challenges in amorphous solid dispersion with rational development of biorelevant dissolution-permeation method

Hot-melt extrusion is often used to prepare amorphous solid dispersion to overcome low drug solubility and enhance bio-performance of the formulation. Due to the uniqueness of each drug - polymer combination and its physico-chemical properties, setting the appropriate HME barrel temperature, feed rate and screw speed ensures drug amorphization, absence of residual crystallinity, absence of water, and a suitable drug release profile. In this research, samples with BCS II/IV model drug and PVP/VA polymer were prepared to evaluate the impact of HME process parameters, incoming drug form (anhydrous vs. hydrate), and drug supplier (i.e., impurity profile), on biorelevant drug release. This study provides a relationship between observed in vitro supersaturation and precipitation behavior of amorphous solid dispersion formulation with in vivo results, on patients, by using the acceptor profile of side-by-side dissolution-permeation apparatus. An in vitro dissolution method, in small volumes, in an apparatus with paddles and dissolution-permeation side-by-side method was developed on the MicroFlux™ apparatus to assess if the differences observed in vitro bears relevance to the bioequivalence outcome in vivo. The former was used to guide the generic drug product development due to high discriminatory strength, while the latter was biorelevant, due to the inclusion of the second compartment assuring absorptive environment to capture the impact of supersaturation and subsequent precipitation on bioavailability. Bio-relevancy of the in vitro method was confirmed with the in vivo dog study and clinical study on patients, and an in vitro - in vivo correlation was established. For the investigated BCS II/IV drug, this research highlights the importance of considering supersaturation and formation of colloidal species during amorphous solid dispersion release testing to assure product quality, safety and efficacy.

The effect of anionic Eudragit polymers on drug supersaturation and in vitro permeation improvement

OBJECTIVES

In the present study, Cinnarizine was selected as a weakly basic drug with poor aqueous solubility to investigate the supersaturation maintaining the ability of different types of anionic Eudragit polymers (Eudragits L100-55, L100 and S100). Furthermore, the interplay between polymer-mediated supersaturation maintenance and in vitro permeation enhancement was studied.

METHODS

The effect of Eudragit polymers on the pH-induced supersaturation of Cinnarizine was examined under different pHs (6.4, 6.8 and 7.8). Moreover, the effect of Eudragit polymers on the permeation of Cinnarizine through the Caco-2 membrane was investigated.

RESULTS

The aggregate size of Eudragit polymers in solution was determined and it was found that the size of polymer aggregate was bigger when lower pH or more hydrophobic polymer was used, which corresponded strongly with improved drug supersaturation. Based on the findings, hydrophobic Cinnarizine-polymer interactions seemed to be essential in determining the impact of Eudragit polymers on maintaining the Cinnarizine supersaturation. The permeation study demonstrated that the rate of drug permeation through the Caco-2 membrane increased in the presence of Eudragit polymers, but their effect on maintaining supersaturation was more significant than their effect on the drug permeation rate. Moreover, the highest level of Cinnarizine supersaturation observed in a non-permeation condition did not correlate with the optimal absorption in a permeation condition.

CONCLUSION

This study revealed that the integration of permeation and supersaturation assays is needed to reliably predict the impact of supersaturation maintenance by polymers on the absorption of poorly soluble drugs.

In-vitro dynamic dissolution/bioconversion/permeation of fosamprenavir using a novel tool with an artificial biomimetic permeation barrier and microdialysis-sampling

Fosamprenavir is a phosphate ester prodrug that, upon dissolution, is cleaved to the poorly soluble yet readily absorbable parent drug amprenavir. In this study, a novel cell-free in vitro setup with quasi-continuous monitoring of the dynamic dissolution/bio-conversion/permeation of fosamprenavir was designed and tested. It consists of side-by-side diffusion cells, where the donor and acceptor compartments are separated by the biomimetic barrier PermeaPad®, and sampling from the donor compartment is accomplished via a microdialysis probe. Externally added bovine alkaline phosphatase induced bioconversion in the donor compartment. Microdialysis sampling allowed to follow the enzymatic conversion of fosamprenavir to amprenavir by the bovine alkaline phosphatase in an (almost) real-time manner eliminating the need to remove or inactivate the enzyme. Biomimetic conversion rates in the setup were established by adding appropriate amounts of the alkaline phosphatase. A substantial (6.5-fold) and persistent supersaturation of amprenavir was observed due to bioconversion at lower (500 µM) concentrations, resulting in a substantially increased flux across the biomimetic barrier, nicely reflecting the situation in vivo. At conditions with an almost 10-fold higher dose than the usual human dose, some replicates showed premature precipitation and collapse of supersaturation, while others did not. In conclusion, the proposed novel tool appears very promising in gaining an in-depth mechanistic understanding of the bioconversion/permeation interplay, including transient supersaturation of phosphate-ester prodrugs like fosamprenavir.

Aliskiren Hemifumarate Proliposomes for Improved Oral Drug Delivery: Formulation Development, In Vitro and In Vivo Permeability Testing

The objective of this study was to develop proliposomal formulations for a poorly bioavailable drug, aliskiren hemifumarate (AKH). A solvent evaporation method was used to prepare proliposomes using different lipids. The lipids of selection were soy phosphatidylcholine (SPC), dimyristoylphosphatidylcholine (DMPC), and dimyristoylphosphatidylglycerol sodium (DMPG Na), stearylamine, and cholesterol in various ratios. Proliposomes were evaluated for particle size, zeta potential, in vitro drug release, in vitro permeability, and in vivo pharmacokinetics upon hydration with aqueous phase. In vitro drug release studies were conducted in 0.01 N hydrochloric acid using USP type II dissolution apparatus. Parallel artificial membrane permeation assay (PAMPA) and Caco-2 cell line models were used to study the in vitro drug permeation. Male Sprague-Dawley (SD) rats were used to conduct in vivo pharmacokinetic studies. Among different formulations, proliposomes with drug/DMPC/cholesterol/stearylamine in the ratio of 1:5:0.025:0.050 (w/w/w/w) demonstrated the desired particle size, higher zeta potential, and higher encapsulation efficiency. The PAMPA and Caco-2 cell line experiments showed a significantly higher permeability of AKH with proliposomes as compared to pure AKH. In animal studies, the optimized formulation of proliposomes showed significant improvement in the rate and extent of absorption of AKH. Specifically, following a single oral administration, the relative bioavailability of AKH proliposome formulation was 230% when compared to pure AKH suspension.

An Insight into Eudragit S100 Preserving Mechanism of Cinnarizine Supersaturation

Generally, supersaturation of weakly basic drug solution in the gastrointestinal tract can be followed by precipitation, and this can compromise the bioavailability of drugs. The purpose of this study was to evaluate the effect of Eudragit® S100 on the pH-induced supersaturation of cinnarizine and to examine the preserving mechanism of cinnarizine supersaturation by Eudragit®. Variables, including pH of media, ionic strength, and degree of supersaturation, were studied to investigate the effects of these parameters on cinnarizine supersaturation in the presence and absence of Eudragit®. The size of the Eudragit® aggregate in solution using dynamic light scattering was determined. The effect of Eudragit® on the transport of cinnarizine through the Caco-2 membrane was also investigated. The particle size study of Eudragit® aggregates showed that the size of these aggregates become large when the pH was lowered. Supersaturation experiments also demonstrated that Eudragit® preserved higher cinnarizine supersaturation with increasing ionic strength of the solution. The phase separation behavior of cinnarizine solution as a function of the degree of the supersaturation could be readily explained by considering the drug amorphous solubility. In vitro permeation studies revealed that the rate of cinnarizine permeation across Caco-2 cells increased in the presence of Eudragit®. According to the obtained results, the aggregation status of Eudragit® and nonspecific hydrophobic cinnarizine-Eudragit® interactions seemed to be essential in determining the effect of Eudragit® on cinnarizine supersaturation.

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.

Combined Methodologies for Determining In Vitro Bioavailability of Drugs and Prediction of In Vivo Bioequivalence From Pharmaceutical Oral Formulations

With the aim of developing an in vitro model for the bioavailability (BA) prediction of drugs, we focused on the study of levonorgestrel (LVN) released by 1.5 mg generic and brand-name tablets. The developed method consisted in combining a standard dissolution test with an optimized parallel artificial membrane permeability assay (PAMPA) to gain insights into both drug release and gastrointestinal absorption. Interestingly, the obtained results revealed that the tablet standard dissolution test, combined with an optimized PAMPA, highlighted a significant decrease in the release (15 ± 0.01 μg min⁻¹ vs 30 ± 0.01 μg min⁻¹) and absorption (19 ± 7 × 10^–6 ± 7 cm/s Pe vs 41 ± 15 × 10^–6 cm/s Pe) profiles of a generic LVN tablet when compared to the brand-name formulation, explaining unbalanced in vivo bioequivalence (BE). By using this new approach, we could determine the actual LVN drug concentration dissolved in the medium, which theoretically can permeate the gastrointestinal (GI) barrier. In fact, insoluble LVN/excipient aggregates were found in the dissolution media giving rise to non-superimposable dissolution profiles between generic and brand-name LVN tablets. Hence, the results obtained by combining the dissolution test and PAMPA method provided important insights confirming that the combined methods can be useful in revealing crucial issues in the prediction of in vivo BE of drugs.

An overview of in vitro, ex vivo and in vivo models for studying the transport of drugs across intestinal barriers

Oral administration is the most commonly used route for drug delivery owing to its cost-effectiveness, ease of administration, and high patient compliance. However, the absorption of orally delivered compounds is a complex process that greatly depends on the interplay between the characteristics of the drug/formulation and the gastrointestinal tract. In this contribution, we review the different preclinical models (in vitro, ex vivo and in vivo) from their development to application for studying the transport of drugs across intestinal barriers. This review also discusses the advantages and disadvantages of each model. Furthermore, the authors have reviewed the selection and validation of these models and how the limitations of the models can be addressed in future investigations. The correlation and predictability of the intestinal transport data from the preclinical models and human data are also explored. With the increasing popularity and prevalence of orally delivered drugs/formulations, sophisticated preclinical models with higher predictive capacity for absorption of oral formulations used in clinical studies will be needed.

Oral delivery of protein-based therapeutics: Gastroprotective strategies, physiological barriers and in vitro permeability prediction

The number of biological molecules emerging as therapeutics is growing exponentially due to their higher specificity and tolerability profiles compared to small molecules. Despite this, their traditionally parenteral delivery often results in poor patient compliance and incomplete treatment. Current research is focussed on developing effective oral delivery strategies to facilitate administration of these biomolecules, however no universal method exists to simultaneously provide gastric protection as well as enhance transport across the gastrointestinal epithelium. Furthermore, for efficient formulation development it is imperative that we can reliably analyse permeability of biomolecules through the gastrointestinal tract, highlighting the importance of the continual development and ongoing evaluation of in vitro predictive permeability tools. Here, we review the physiological obstacles associated with peptide and protein delivery throughout the gastrointestinal tract. Furthermore, we highlight methods utilised to circumvent these barriers and promote improved intestinal permeability. Lastly, we explore in vitro models employed to predict epithelial transport. Key findings highlight the need to carefully understand gastrointestinal physiology, allowing specific engineering of oral delivery systems for biomolecules. Significant importance is placed upon understanding enzymatic degradation susceptibility as well as uptake mechanisms for particulate and protein-based therapeutics for the development of successful oral protein delivery platforms.

Drug permeability profiling using cell-free permeation tools: Overview and applications

Cell-free permeation systems are gaining interest in drug discovery and development as tools to obtain a reliable prediction of passive intestinal absorption without the disadvantages associated with cell- or tissue-based permeability profiling. Depending on the composition of the barrier, cell-free permeation systems are classified into two classes including (i) biomimetic barriers which are constructed from (phospho)lipids and (ii) non-biomimetic barriers containing dialysis membranes. This review provides an overview of the currently available cell-free permeation systems including Parallel Artificial Membrane Permeability Assay (PAMPA), Phospholipid Vesicle-based Permeation Assay (PVPA), Permeapad®, and artificial membrane based systems (e.g. the artificial membrane insert system (AMI-system)) in terms of their barrier composition as well as their predictive capacity in relation to well-characterized intestinal permeation systems. Given the potential loss of integrity of cell-based permeation barriers in the presence of food components or pharmaceutical excipients, the superior robustness of cell-free barriers makes them suitable for the combined dissolution/permeation evaluation of formulations. While cell-free permeation systems are mostly applied for exploring intestinal absorption, they can also be used to evaluate non-oral drug delivery by adjusting the composition of the membrane.

In vitro models to estimate drug penetration through the compromised stratum corneum barrier

OBJECTIVES

The phospholipid vesicle-based permeation assay (PVPA) is a recently established in vitro stratum corneum model to estimate the permeability of intact and healthy skin. The aim here was to further evolve this model to mimic the stratum corneum in a compromised skin barrier by reducing the barrier functions in a controlled manner.

METHODS

To mimic compromised skin barriers, PVPA barriers were prepared with explicitly defined reduced barrier function and compared with literature data from both human and animal skin with compromised barrier properties. Caffeine, diclofenac sodium, chloramphenicol and the hydrophilic marker calcein were tested to compare the PVPA models with established models.

RESULTS AND DISCUSSIONS

The established PVPA models mimicking the stratum corneum in healthy skin showed good correlation with biological barriers by ranking drugs similar to those ranked by the pig ear skin model and were comparable to literature data on permeation through healthy human skin. The PVPA models provided reproducible and consistent results with a distinction between the barriers mimicking compromised and healthy skin. The trends in increasing drug permeation with an increasing degree of compromised barriers for the model drugs were similar to the literature data from other in vivo and in vitro models.

CONCLUSIONS

The PVPA models have the potential to provide permeation predictions when investigating drugs or cosmeceuticals intended for various compromised skin conditions and can thus possibly reduce the time and cost of testing as well as the use of animal testing in the early development of drug candidates, drugs and cosmeceuticals.

Biomimetic PVPA in vitro model for estimation of the intestinal drug permeability using fasted and fed state simulated intestinal fluids

A prerequisite for successful oral drug therapy is the drug's ability to cross the gastrointestinal barrier. Considering the increasing number of new chemical entities in modern drug discovery, reliable and fast in vitro models are required for early and efficient prediction of intestinal permeability. To mimic the intestinal environment, use of biorelevant media may provide valuable information on in vivo drug permeation. The present study aims at improving the novel biomimetic phospholipid vesicle-based permeation assay's (PVPAbiomimetic) biorelevance by investigating the applicability of the biorelevant media; fasted state simulated intestinal fluid (FaSSIF) and fed state simulated intestinal fluid (FeSSIF). The FaSSIF and FeSSIF's influence on the permeability of the model drugs acyclovir, indomethacin, griseofulvin and nadolol was then assessed. The barriers' robustness in terms of storage stability was also evaluated. The barriers were found to maintain their integrity in presence of FaSSIF and FeSSIF. The model drugs showed changes in permeability in presence of the different simulated intestinal fluids that were in agreement with previous reports. Moreover, the barrier showed improved storage stability by maintaining its integrity for 6months. Altogether, this study moves the PVPAbiomimetic an important step towards a better in vitro permeability model for use in drug development.

Liposomes for (trans)dermal drug delivery: the skin-PVPA as a novel in vitro stratum corneum model in formulation development

Penetration potential of vesicles destined for trans(dermal) administration remains to be of great interests both in respect to drug therapy and cosmetic treatment. This study investigated the applicability of the phospholipid vesicle-based permeation assay (PVPA) as a novel in vitro skin barrier model for screening purposes in preformulation studies. Various classes of liposomes containing hydrophilic model drug were examined, including conventional liposomes (CLs), deformable liposomes (DLs) and propylene glycol liposomes (PGLs). The size, surface charge, membrane deformability and entrapment efficiency were found to be affected by the vesicle lipid concentration, the presence of the surfactant and propylene glycol. All liposomes exhibited prolonged drug release profiles with an initial burst effect followed by a slower release phase. The permeation of the drug from all of the tested liposomes, as assessed with the mimicked stratum corneum--PVPA model, was significantly enhanced as compared to the permeability of the drug in solution form. Although the DLs and the PGLs exhibited almost the same membrane elasticity, the permeability of the drug delivered by PGLs was higher (6.2 × 10⁻⁶ cm/s) than DLs (5.5 × 10⁻⁶ cm/s). Therefore, this study confirmed both the potential of liposomes as vesicles in trans(dermal) delivery and potential of the newly developed skin-PVPA for the screening and optimization of liposomes at the early preformulation stage.

Melt extrusion with poorly soluble drugs

Melt extrusion (ME) over recent years has found widespread application as a viable drug delivery option in the drug development process. ME applications include taste masking, solid-state stability enhancement, sustained drug release and solubility enhancement. While ME can result in amorphous or crystalline solid dispersions depending upon several factors, solubility enhancement applications are centered around generating amorphous dispersions, primarily because of the free energy benefits they offer. In line with the purview of the current issue, this review assesses the utility of ME as a means of enhancing solubility of poorly soluble drugs/chemicals. The review describes major processing aspects of ME technology, definition and understanding of the amorphous state, manufacturability, analytical characterization and biopharmaceutical performance testing to better understand the strength and weakness of this formulation strategy for poorly soluble drugs. In addition, this paper highlights the potential advantages of employing a fusion of techniques, including pharmaceutical co-crystals and spray drying/solvent evaporation, facilitating the design of formulations of API exhibiting specific physico-chemical characteristics. Finally, the review presents some successful case studies of commercialized ME based products.

Amorphous solid dispersion enhances permeation of poorly soluble ABT-102: true supersaturation vs. apparent solubility enhancement

Amorphous solid dispersions (ASDs) represent a promising formulation approach for poorly soluble drugs. We explored the formulation-related impact of ASDs on permeation rate, apparent solubility and molecular solubility of the poorly soluble drug ABT-102. The influence of fasted state simulated intestinal fluid (FaSSIF) as dispersion medium was also studied. ASDs were prepared by hot-melt extrusion. Permeation rate was assessed by the Caco-2 transwell assay. Cell viability and barrier integrity were assured by AlamarBlue©, TEER and permeability of the hydrophilic marker carboxyfluorescein. Apparent solubility and molecular solubility were evaluated by using centrifugation and inverse dialysis, respectively. The in vitro permeation rate of ABT-102 from aqueous dispersions of the ASD was found 4 times faster than that from the dispersions of the crystals, while apparent solubility and molecular solubility of ABT-102 were increased. Yet, a further increase in apparent solubility due to micellar solubilization as observed when dispersing the ASD in FaSSIF, did not affect molecular solubility or permeation rate. Overall, a good correlation between permeation rate and molecular solubility but not apparent solubility was seen.

Impact of FaSSIF on the solubility and dissolution-/permeation rate of a poorly water-soluble compound

The poorly water-soluble drug ABT-102, a potent TRPV1 (transient receptor potential cation channel subfamily V member 1) antagonist, was investigated in terms of its solubility and dissolution-permeation rate across Caco-2 cell monolayers in the presence and absence of fasted state simulated intestinal fluid (FaSSIF). ABT-102 showed a more than 30-fold higher apparent solubility in FaSSIF, compared to Hank's balanced salt solution (HBSS). On the other hand, the amount of truly dissolved API in the suspension, as assessed by inverse dialysis, was found hardly influenced by FaSSIF. Neither the drug nor FaSSIF adversely affected cell viability or integrity of the Caco-2 monolayer. P-gp-inhibition experiments confirmed that the drug was not a substrate of the export pump. The flux of ABT-102 across the Caco-2 barrier was found virtually the same in FaSSIF and in buffer, i.e. in vitro overall dissolution-/permeation rate of ABT-102 from suspensions appears not affected by its enhanced apparent solubility due to association with TC/PC-micelles.

In-vitro permeability of poorly water soluble drugs in the phospholipid vesicle-based permeation assay: the influence of nonionic surfactants

Objectives

The aim of this study was to determine the influence of nonionic surfactants on drug permeability using the phospholipid vesicle-based permeation assay (PVPA), which excludes other than trans-membrane diffusion pathways.

Methods

Barrier integrity was monitored both by electrical resistance and permeability measurement of the hydrophilic marker calcein. Permeability of the model drugs ketoprofen and nadolol across the PVPA-barrier was measured by HPLC-UV. Micelle association of the model drugs was determined using ultrafiltration, whereby micelle-bound drug and molecular drug were separated.

Key findings

The nonionic surfactant poloxamer 188 was demonstrated not to affect barrier integrity. Drug permeability was found depressed in the presence of poloxamer 188 in a concentration-dependent manner. Both drugs were found to associate with poloxamer 188 micelles. The extent of the decrease in permeability correlated mostly, but not in all cases, with the fraction of micelle-bound drug.

Conclusions

Micelle association was one important but not the only factor affecting drug permeability across the PVPA-barrier.