Polymeric Precipitation Inhibitors Promote Fenofibrate Supersaturation and Enhance Drug Absorption from a Type IV Lipid-Based Formulation

Co-milling of glass forming ability class III drugs: Comparing the impact of low and high glass transition temperatures

With an increasing focus on sustainable technologies in the pharmaceutical industry, milling provides a solvent-free approach to improve drug dissolution. Milling of drugs with an excipient offers additional opportunities to achieve supersaturation kinetics. Therefore, this work aims to present insights of co-milling fenofibrate and apremilast, two good glass formers with low and high glass transition temperatures (Tgs) respectively. Drugs were co-milled with croscarmellose sodium for various process durations followed by thermal analysis, investigation of crystallinity, surface area and dissolution. The dissolution enhancement of the low-Tg glass former fenofibrate highly correlated with the process-induced increase in surface area of co-milled systems (R2 = 0.96). In contrast, the high-Tg glass former apremilast lost its crystalline order gradually after ≥ 10 min of co-milling, and favourable supersaturation kinetics during biorelevant dissolution testing were observed. Interestingly, the melting point of co-milled apremilast decreased and linearly correlated with the highest measured drug concentration (cmax) during in vitro dissolution (onset temperature R2 = 0.98; peak temperature R2 = 0.96). The melting point depression remained stable after 90 days for apremilast, whereas fenofibrate co-milled for 20 min or more showed an increase in melting point upon storage. This study demonstrated that co-milling with croscarmellose sodium is ideally suited to good glass formers with a high Tg. The melting point depression is thereby proposed as an easily accessible critical quality attribute to estimate likely dissolution performance of drugs in dry co-milled formulations.

Exploring supersaturated type IV lipid-based formulations: Impact of supersaturation, digestion and precipitation wInhibition on cinnarizine absorption

Building up on previous publications for type I, II, IIIa, and IIIb Lipid-based formulations (LBFs), the supersaturation potential for cinnarizine in type IV LBFs and the effect of supersaturation, lipid digestion, and precipitation inhibition in vivo was investigated. The supersaturation potential for cinnarizine-loaded type IV LBFs was high and this was investigated in vivo in rats. Supersaturated LBFs tended to show higher drug exposures in vivo than their non-supersaturated counterparts (22 - 92 % increase in AUC0-24h, not dose-normalized), but this was only statistically significant for the formulation containing a precipitation inhibitor under lipase-inhibited conditions, so the overall impact was limited. Soluplus® as a precipitation inhibitor did not increase drug exposure in general, even though the administered cinnarizine dose was higher for the supersaturated formulations. Lipase inhibition had no impact on cinnarizine absorption, indicating no increased precipitation during digestion. The results were in line with previous findings from type IIIb LBFs that revealed that the digestion process was less important for drug absorption from hydrophilic types of LBFs as opposed to the more lipophilic type I- and II systems.

Continuing along the lipid formulation classification system: Effects of lipid chain length, supersaturation, digestion, and precipitation inhibition on cinnarizine absorption from type IIIa lipid-based formulations

Lipid-based formulations (LBFs) are classified according to the content of each component and the hydrophilicity of the surfactant into types I - IV, with LBFs type IIIa consisting of 40 - 80 % oils, 20 - 40 % water-soluble surfactant with HLB > 12, and 0 - 40 % cosolvents. In cases where high drug loads are required, e.g. preclinical toxicity-studies, and the solubility of the drug in the vehicle is insufficient, the use of supersaturated LBFs has been suggested. The impact of digestion on drug absorption from cinnarizine-loaded type I and type II LBFs had previously been found to be highly important for the bio-performance, however, the IIIa systems self-emulsify which is why digestion may be less critical. Therefore, the impact of digestion on drug absorption, as well as the impact of lipid chain length, supersaturation and the addition of the precipitation inhibitor Soluplus® has been investigated in the present work for LBF class IIIa formulations using cinnarizine as a model compound in a similar manner as the previous studies on LBF classes I and II. The administration of long-chain (LC) based type IIIa formulations resulted in a similar drug exposure as for medium-chain (MC) based systems. Supersaturation was beneficial in all cases, with an increase in AUC0-24h of 72 - 178 % and in Cmax of 45 - 130 %. Upon lipase inhibition, AUC0-24h tended to decrease by 28 - 35 % for LC-based formulations. For MC-based formulations, there was an increase in the AUC0-24h of up to 31 % compared to the formulations without lipase inhibition, however, if Soluplus® was present, the AUC0-24h for MC-based formulations tended to decrease. The addition of Soluplus® only brought a benefit for non-supersaturated LBFs, with a 26 - 34 % increase in AUC0-24h, and for supersaturated MC-based formulations without lipase inhibition, but not for the other formulations. This was surprising as the administered dose of cinnarizine in supersaturated LBFs containing the precipitation inhibitor was higher than in supersaturated LBFs without Soluplus®.

Influence of polymer and surfactant-based precipitation inhibitors on supersaturation-driven absorption of Ibrutinib from high-dose lipid-based formulations

There is a growing pharmaceutical interest in supersaturated lipid-based formulations (Super-LbF) as an innovative strategy to enhance drug loading capacities while simultaneously reducing pill burden. This approach involves increasing the drug concentration above its equilibrium solubility in a lipid solution, achieved through temperature-induced supersaturation or the dissolution of lipophilic ionic salts. However, the physical instability and potential drug precipitation upon the dispersion of LbF remain critical. The focus of this work was to assess the impact of polymer and surfactant as precipitation inhibitors (PIs) in Super-LbF and investigate whether PIs can effectively address the aforementioned challenges. Ibrutinib (Ibr) was selected as a model drug due to its limited solubility and dissolution characteristics. The optimized formulations were characterized with a focus on dispersibility, lipolysis-permeation, and physical stability during storage. The inclusion of PIs in Super-LbF significantly enhanced physical stability by increasing viscosity and reducing the degree of supersaturation through elevated equilibrium solubility. During the dispersion and digestion study, varying levels of transient supersaturation were observed for both Super-LbF and PI-loaded Super-LbF. A noteworthy 2.5 to 3-fold increase in the solubilization ratio was observed for PI-loaded Super-LbF in comparison to Super-LbF without PI. This increase indicates a significant rise in transient drug supersaturation through kinetic and thermodynamic precipitation inhibition mechanisms. Moreover, lipolysis-permeation studies revealed increased flux values with enhanced solubilization, except in the case of Pluronic® F68, which exhibited a reduced free drug concentration near the Permeapad® barrier. Further, the in vivo absorption study confirmed that prolonged supersaturation, facilitated by PIs, contributed to enhancement in drug exposure in rats. PI-loaded Super-LbFs demonstrated a significant improvement (5.1 to 8.9-fold) in the absorption profile compared to Super-LbF without PI (p < 0.001). The study results indicate that incorporating PIs into Super-LbF enhances physical stability and maintains transient drug supersaturation under digestive conditions. Overall, this formulation approach shows promise for expanding the application of LbF to enable the successful oral delivery of high-dose regimen drugs.

Enhancing oral bioavailability of dasatinib via supersaturable SNEDDS: Investigation of precipitation inhibition and IVIVC through in-vitro lipolysis-permeation model

Dasatinib (DASA), a potent second-generation multitarget kinase inhibitor marketed as Sprycel® (Tablet), is limited by poor oral bioavailability (14-24 %) and dose-related gastrointestinal side effects. A supersaturable self-nanoemulsifying drug delivery system (su-SNEDDS) designed to enhance DASA's solubility, sustain supersaturation, and improve oral bioavailability. The su-SNEDDS formulation comprises DASA, an oil, surfactant, co-surfactant, and polyvinylpyrrolidone (PVP) K30 as a precipitation inhibitor (PI). This innovative system demonstrated exceptional stability in gastrointestinal fluids and robustness against dilution, maintaining significantly elevated drug concentrations in the aqueous milieu. su-SNEDDS achieved ∼ 13.5-fold and 2-fold higher aqueous drug concentrations than DASA suspension and SNEDDS without PI, respectively, after 60 min of digestion. This improvement is attributed to the inhibition of crystal growth by PVP K30. In-vitro lipolysis-permeation and Caco-2 cell assays revealed significantly enhanced drug permeation with su-SNEDDS compared to DASA suspension and SNEDDS without PI. In-vivo pharmacokinetic studies further demonstrated ∼ 1.9-fold and 2.7-fold higher AUC compared to SNEDDS without PI and drug suspension, respectively. A linear correlation (R2 = 0.9042) was established between the AUC data obtained from in-vitro vs in-vivo study. These findings underscore the potential of su-SNEDDS to significantly enhance DASA's solubility, permeation and oral bioavailability, presenting a substantial advancement in pharmaceutical drug delivery systems. Moreover, in-vitro lipolysis-permeation could be promising tool to predict the in-vivo fate of the oral SNEDDS formulations.

Benefits of combining supersaturating and solubilizing formulations - Is two better than one?

A variety of enabling formulations has been developed to address poor oral drug absorption caused by insufficient dissolution in the gastrointestinal tract. As the in vivo performance of these formulations is a result of a complex interplay between dissolution, digestion and permeation, development of suitable in vitro assays that captures these phenomena are called for. The enabling-absorption (ENA) device, consisting of a donor and receiver chamber separated by a semipermeable membrane, has successfully been used to study the performance of lipid-based formulations. In this work, the ENA device was prepared with two different setups (a Caco-2 cell monolayer and an artificial lipid membrane) to study the performance of a lipid-based formulation (LBF), an amorphous solid dispersion (ASD) and the potential benefit of combining the two formulation strategies. An in vivo pharmacokinetic study in rats was performed to evaluate the in vitro-in vivo correlation. In the ENA, high drug concentrations in the donor chamber did not translate to a high mass transfer, which was particularly evident for the ASD as compared to the LBF. The solubility of the polymer used in the ASD was strongly affected by pH-shifts in vitro, and the ph_dependence resulted in poor in vivo performance of the formulation. The dissolution was however increased in vitro when the ASD was combined with a blank lipid-based formulation. This beneficial effect was also observed in vivo, where the drug exposure of the ASD increased significantly when the ASD was co-administered with the blank LBF. To conclude, the in vitro model managed to capture solubility limitations and strategies to overcome these for one of the formulations studied. The correlation between the in vivo exposure of the drug exposure and AUC in the ENA was good for the non pH-sensitive formulations. The deconvoluted pharmacokinetic data indicated that the receiver chamber was a better predictor for the in vivo performance of the drug, however both chambers provided valuable insights to the observed outcome in vivo. This shows that the advanced in vitro setting used herein successfully could explain absorption differences of highly complex formulations.

Thermally-Induced Supersaturation Approach for Optimizing Drug Loading and Biopharmaceutical Properties of Supersaturated Lipid-Based Formulations: Case Studies with Ibrutinib and Enzalutamide

Lipid-based formulations (LbFs) have demonstrated success in pharmaceutical applications; however, challenges persist in dissolving entire doses of the drug into defined liquid volumes. In this study, the temperature-induced supersaturation method was employed in LbF to address drug loading and pill burden issues. Supersaturated LbFs (super-LbF) were prepared using the temperature-induced supersaturation method, where the drug load is above its equilibrium solubility. Further, the influence of the drug's physicochemical and thermal characteristics on drug loading and their relevance with an apparent degree of supersaturation (aDS) was studied using two model drugs, ibrutinib and enzalutamide. All the prepared LbFs were evaluated in terms of physical stability, dispersion, and solubilization capacity, as well as pharmacokinetic assessments. Drug re-crystallization was observed in the lipid solution on long-term storage at higher aDS values of 2-2.5. Furthermore, high-throughput lipolysis studies demonstrated a significant decrease in drug concentration across all LbFs (regardless of drug loading) due to a decline in the formulation solvation capacity and subsequent generation of in-situ supersaturation. Further, the in vivo results demonstrated comparable pharmacokinetic parameters between conventional LbF and super-LbF. The short duration of the thermodynamic metastable state limits the potential absorption benefits. However, super-LbFs of Ibr and Enz showed superior profiles, with 1.7-fold and 5.2-fold increased drug exposure compared to their respective crystalline suspensions. In summary, this study emphasizes the potential of temperature-induced supersaturation in LbF for enhancing drug loading and highlights the intricate interplay between drug properties, formulation characteristics, and in vivo performance.

Lipid-based systems with precipitation inhibitors as formulation approach to improve the drug bioavailability and/or lower its dose: a review

Lipid-based systems, such as self-microemulsifying systems (SMEDDS) are attracting strong attention as a formulation approach to improve the bioavailability of poorly water-soluble drugs. By applying the "spring and parachute" strategy in designing supersaturable SMEDDS, it is possible to maintain the drug in the supersaturated state long enough to allow absorption of the complete dose, thus improving the drug's bio-availability. As such an approach allows the incorporation of larger amounts of the drug in equal or even lower volumes of SMEDDS, it also enables the production of smaller final dosage forms as well as decreased gastrointestinal irritation, being of particular importance when formulating dosage forms for children or the elderly. In this review, the technological approaches used to prolong the drug supersaturation are discussed regarding the type and concentration of polymers used in liquid and solid SMEDDS formulation. The addition of hypromellose derivatives, vinyl polymers, polyethylene glycol, polyoxyethylene, or polymetacrylate copolymers proved to be effective in inhibiting drug precipitation. Regarding the available literature, hypromellose has been the most commonly used polymeric precipitation inhibitor, added in a concentration of 5 % (m/m). However, the inhibiting ability is mainly governed not only by the physicochemical properties of the polymer but also by the API, therefore the choice of optimal precipitation inhibitor is recommended to be evaluated on an individual basis.

Development and characterization of solid lipid-based formulations (sLBFs) of ritonavir utilizing a lipolysis and permeation assay

As a high number of active pharmaceutical ingredients (APIs) under development belong to BCS classes II and IV, the need for improving bioavailability is critical. A powerful approach is the use of lipid-based formulations (LBFs) that usually consist of a combination of liquid lipids, cosolvents, and surfactants. In this study, ritonavir loaded solid LBFs (sLBFs) were prepared using solid lipid excipients to investigate whether sLBFs are also capable of improving solubility and permeability. Additionally, the influence of polymeric precipitation inhibitors (PVP-VA and HPMC-AS) on lipolysis triggered supersaturation and precipitation was investigated. One step intestinal digestion and bicompartmental permeation studies using an artificial lecithin-in-dodecane (LiDo) membrane were performed for each formulation. All formulations presented significantly higher solubility (5 to >20-fold higher) during lipolysis and permeation studies compared to pure ritonavir. In the combined lipolysis-permeation studies, the formulated ritonavir concentration increased 15-fold in the donor compartment and the flux increased up to 71 % as compared to non-formulated ritonavir. The formulation with the highest surfactant concentration showed significantly higher ritonavir solubility compared to the formulation with the highest amount of lipids. However, the precipitation rates were comparable. The addition of precipitation inhibitors did not influence the lipolytic process and showed no significant benefit over the initial formulations with regards to precipitation. While all tested sLBFs increased the permeation rate, no statistically significant difference was noted between the formulations regardless of composition. To conclude, the different release profiles of the formulations were not correlated to the resulting flux through a permeation membrane, further supporting the importance of making use of combined lipolysis-permeation assays when exploring LBFs.

Early evaluation of opportunities in oral delivery of PROTACs to overcome their molecular challenges

PROteolysis TArgeting Chimeras (PROTACs) offer new opportunities in modern medicine by targeting proteins that are intractable to classic inhibitors. Heterobifunctional in nature, PROTACs are small molecules that offer a unique mechanism of protein degradation by hijacking the ubiquitin-mediated protein degradation pathway, known as the ubiquitin-proteasome system. Herein, we present an analysis on the structural characteristics of this novel chemical modality. Furthermore, we review and discuss the formulation opportunities to overcome the oral delivery challenges of PROTACs in drug discovery.

Lipid based formulations as supersaturating oral delivery systems: From current to future industrial applications

Lipid-based formulations, in particular supersaturated lipid-based formulations, are important delivery approaches when formulating challenging compounds, as especially low water-soluble compounds profit from delivery in a pre-dissolved state. In this article, the classification of lipid-based formulation is described, followed by a detailed discussion of different supersaturated lipid-based formulations and the recent advances reported in the literature. The supersaturated lipid-based formulations discussed include both the in situ forming supersaturated systems as well as the thermally induced supersaturated lipid-based formulations. The in situ forming drug supersaturation by lipid-based formulations has been widely employed and numerous clinically available products are on the market. There are some scientific gaps in the field, but in general there is a good understanding of the mechanisms driving the success of these systems. For thermally induced supersaturation, the technology is not yet fully understood and developed, hence more research is required in this field to explore the formulations beyond preclinical studies and initial clinical trials.

Comparative analysis of drug-salt-polymer interactions by experiment and molecular simulation improves biopharmaceutical performance

The propensity of poorly water-soluble drugs to aggregate at supersaturation impedes their bioavailability. Supersaturated amorphous drug-salt-polymer systems provide an emergent approach to this problem. However, the effects of polymers on drug-drug interactions in aqueous phase are largely unexplored and it is unclear how to choose an optimal salt-polymer combination for a particular drug. Here, we describe a comparative experimental and computational characterization of amorphous solid dispersions containing the drug celecoxib, and a polymer, polyvinylpyrrolidone vinyl acetate (PVP-VA) or hydroxypropyl methylcellulose acetate succinate, with or without Na+/K+ salts. Classical models for drug-polymer interactions fail to identify the best drug-salt-polymer combination. In contrast, more stable drug-polymer interaction energies computed from molecular dynamics simulations correlate with prolonged stability of supersaturated amorphous drug-salt-polymer systems, along with better dissolution and pharmacokinetic profiles. The celecoxib-salt-PVP-VA formulations exhibit excellent biopharmaceutical performance, offering the prospect of a low-dosage regimen for this widely used anti-inflammatory, thereby increasing cost-effectiveness, and reducing side-effects.

Regorafenib loaded self-assembled lipid-based nanocarrier for colorectal cancer treatment via lymphatic absorption

Oral chemotherapy can improve the life quality of patients; however, the therapeutic effects are limited by low bioavailability and rapid in vivo elimination of anticancer drugs. Here, we developed a regorafenib (REG)-loaded self-assembled lipid-based nanocarrier (SALN) to improve oral absorption and anti-colorectal cancer efficacy of REG through lymphatic absorption. SALN was prepared with lipid-based excipients to utilize lipid transport in the enterocytes and enhance lymphatic absorption of the drug in the gastrointestinal tract. The particle size of SALN was 106 ± 10 nm. SALNs were internalized by the intestinal epithelium via the clathrin-mediated endocytosis, and then transported across the epithelium via the chylomicron secretion pathway, resulting in a 3.76-fold increase in drug epithelial permeability (P_app) compared to the solid dispersion (SD). After oral administration to rats, SALNs were transported by the endoplasmic reticulum, Golgi apparatus, and secretory vesicles of enterocytes and were found in the lamina propria of intestinal villi, abdominal mesenteric lymph, and plasma. The oral bioavailability of SALN was 65.9-fold and 1.70-fold greater than that of the coarse powder suspension and SD, respectively, and was highly dependent on the lymphatic route of absorption. Notably, SALN prolonged the elimination half-life of the drug (9.34 ± 2.51 h) compared to the solid dispersion (3.51 ± 0.46 h), increased the biodistribution of REG in the tumor and gastrointestinal (GI) tract, decreased biodistribution in the liver, and showed better therapeutic efficacy than the solid dispersion in colorectal tumor-bearing mice. These results demonstrated that SALN is promising for the treatment of colorectal cancer via lymphatic transport and has potential for clinical translation.

Amorphous System of Hesperetin and Piperine-Improvement of Apparent Solubility, Permeability, and Biological Activities

The low bioaccessibility of hesperetin and piperine hampers their application as therapeutic agents. Piperine has the ability to improve the bioavailability of many compounds when co-administered. The aim of this paper was to prepare and characterize the amorphous dispersions of hesperetin and piperine, which could help to improve solubility and boost the bioavailability of both plant-origin active compounds. The amorphous systems were successfully obtained by means of ball milling, as confirmed by XRPD and DSC studies. What's more, the FT-IR-ATR study was used to investigate the presence of intermolecular interactions between the systems' components. Amorphization enhanced the dissolution rate as a supersaturation state was reached, as well as improving the apparent solubility of both compounds by 245-fold and 183-fold, respectively, for hesperetin and piperine. In the in vitro permeability studies simulating gastrointestinal tract and blood-brain barrier permeabilities, these increased by 775-fold and 257-fold for hesperetin, whereas they were 68-fold and 66-fold for piperine in the GIT and BBB PAMPA models, respectively. Enhanced solubility had an advantageous impact on antioxidant as well as anti-butyrylcholinesterase activities-the best system inhibited 90.62 ± 0.58% of DPPH radicals and 87.57 ± 1.02% butyrylcholinesterase activity. To sum up, amorphization considerably improved the dissolution rate, apparent solubility, permeability, and biological activities of hesperetin and piperine.

Supersaturation and Precipitation Applicated in Drug Delivery Systems: Development Strategies and Evaluation Approaches

Supersaturation is a promising strategy to improve gastrointestinal absorption of poorly water-soluble drugs. Supersaturation is a metastable state and therefore dissolved drugs often quickly precipitate again. Precipitation inhibitors can prolong the metastable state. Supersaturating drug delivery systems (SDDS) are commonly formulated with precipitation inhibitors, hence the supersaturation is effectively prolonged for absorption, leading to improved bioavailability. This review summarizes the theory of and systemic insight into supersaturation, with the emphasis on biopharmaceutical aspects. Supersaturation research has developed from the generation of supersaturation (pH-shift, prodrug and SDDS) and the inhibition of precipitation (the mechanism of precipitation, the character of precipitation inhibitors and screening precipitation inhibitors). Then, the evaluation approaches to SDDS are discussed, including in vitro, in vivo and in silico studies and in vitro-in vivo correlations. In vitro aspects involve biorelevant medium, biomimetic apparatus and characterization instruments; in vivo aspects involve oral absorption, intestinal perfusion and intestinal content aspiration and in silico aspects involve molecular dynamics simulation and pharmacokinetic simulation. More physiological data of in vitro studies should be taken into account to simulate the in vivo environment. The supersaturation theory should be further completed, especially with regard to physiological conditions.

Effects of Ingested Water Volume on Oral Absorption of Fenofibrate, a BCS Class II Drug, from Micronized and Amorphous Solid Dispersion Formulations in Rats

In this study, we investigated the effects of ingested water volume on the oral absorption of fenofibrate (FEN) with several formulations to confirm the applicability of rats for oral formulation screening. Oral absorption of suspended crystalline FEN was significantly improved by increasing ingested water volume (from 0.5 to 2 mL). FEN absorption improvement by particle size reduction and the linearity in oral absorption by dose escalation suggested that the rate-limiting step of FEN absorption in rats was the dissolution rate, consistent with that in humans. When FEN, as an amorphous solid dispersion (ASD) formulation, was suspended in water followed by immediate administration, oral FEN absorption was significantly higher than when administered in crystalline form and was not influenced by the differences in ingested water volume. Oral absorption of FEN from encapsulated ASD formulation in 1 or 2 mL of water was comparable with that of the suspension form. However, 0.5 mL of water significantly reduced the oral absorption of the solid ASD FEN formulation. These results indicate that to improve the oral absorption of poorly water-soluble drugs when performing a preclinical study with rats, 1 mL of water is the minimum preferable ingested volume to evaluate in vivo formulation performance.

Lipid-based solubilization technology via hot melt extrusion: promises and challenges

INTRODUCTION

Self-emulsifying drug delivery systems (SEDDS) are a promising strategy to improve the oral bioavailability of poorly water-soluble drugs (PWSD). The excipients of SEDDS enable permeation through the mucus and gastro-intestinal barrier, inhibiting efflux transporters (e.g. P-glycoprotein) of drugs. Poor drug loading capacity and formulation instability are the main setbacks of traditional SEDDS. The use of polymeric precipitation inhibitors was shown to create supersaturable SEDDS with increased drug payload, and their solidification can help to overcome the instability challenge. As an alternative to several existing SEDDS solidification technologies, hot melt extrusion (HME) holds the potential for lean and continuous manufacturing of supersaturable solid-SEDDS. Despite being ubiquitously applied in solid lipid and polymeric processing, HME has not yet been widely considered for the preparation of SEDDS.

AREAS COVERED

The review begins with the rationale why SEDDS as the preferred lipid-based delivery systems (LBDS) is suitable for the oral delivery of PWSD and discusses the common barriers to oral administration. The potential of LBDS to surmount them is discussed. SEDDS as the flagship of LBDS for PWSD is proposed with a special emphasis on solid-SEDDS. Finally, the opportunities and challenges of HME from the lipid-based excipient (LBE) processing and product performance standpoint are highlighted.

EXPERT OPINION

HME can be a continuous, solvent-free, cost-effective, and scalable technology for manufacturing solid supersaturable SEDDS. Several critical formulations and process parameters in successfully preparing SEDDS via HME are identified.

Combining lipid based drug delivery and amorphous solid dispersions for improved oral drug absorption of a poorly water-soluble drug

Two widely applied enabling drug delivery approaches, self-nanoemulsifying drug delivery systems (SNEDDS) and amorphous solid dispersions (ASD), were combined, with the aim of enhancing physical stability, solubilization and absorption of the model drug ritonavir. Ritonavir was loaded at a concentration above its saturation solubility (S_eq) in the SNEDDS (superSNEDDS, 250% of S_eq). An ASD of ritonavir with polyvinylpyrrolidone-vinyl acetate copolymers (Kollidon® VA64) was prepared by ball milling. Relevant control formulations, which include conventional SNEDDS (90% of S_eq), superSNEDDS with a physical mix of Kollidon® VA64 and ritonavir (superSNEDDS+PM) and an aqueous suspension of ritonavir were used. A pharmacokinetic (PK) study in rats was performed to assess the relative bioavailability of ritonavir after oral administration. This was followed by evaluating the formulations in a novel two-step in vitro lipolysis model simulating rat gastric and intestinal conditions. The addition of a ritonavir containing ASD to superSNEDDS increased the degree of supersaturation from 250% to 275% S_eq in the superSNEDDS and the physical stability (absence of drug recrystallization) of the system from 48 h to 1 month under ambient conditions. The PK study in rats displayed significantly higher C_max and AUC_0-7h (3-fold increase) and faster T_max for superSNEDDS+ASD compared to the conventional SNEDDS whilst containing 3 times less lipid than the latter. Furthermore, superSNEDDS+ASD were able to keep the drug solubilised during in vitro lipolysis to the same degree as the conventional SNEDDS. These findings suggest that dissolving an ASD in a superSNEDDS can contribute to the development of novel oral delivery systems with increased bioavailability for poorly water-soluble drugs.

Gastroretentive Sustained-Release Tablets Combined with a Solid Self-Micro-Emulsifying Drug Delivery System Adsorbed onto Fujicalin®

Gastroretentive drug delivery systems (GRDDS) get retained in the stomach for a long time, thus facilitating the absorption of drugs in the upper gastrointestinal tract. However, drugs that are difficult to dissolve or unstable in an acidic environment are not suitable for GRDDS. The current study designs GRDDS combined with a self-micro-emulsifying drug delivery system (SMEDDS) for drugs with solubility or stability problems in the stomach. The model drug fenofibrate was formulated into the optimized liquid SMEDDS composed of 50 w/w% Capryol^® PGMC, 40 w/w% Kolliphor^® RH40, and 10 w/w% Transcutol^® HP and solidified through adsorption on several porous adsorbents. In a dissolution medium at pH 1.2, the powdered SMEDDS using Fujicalin^® dissolved quickly and achieved higher drug dissolution than other adsorbents. Based on these results, a gastroretentive bilayer tablet consisting of a drug release layer and a swelling layer was designed. The drug release layer was formulated with the powdered SMEDDS and hydroxypropyl methylcellulose (HPMC) as a release modifier. HPMC was also added to the swelling layer as a water-swellable polymer. The dissolution rate depended on the viscosity of the HPMC in the drug release layer. The time for 90% drug release was extended from 3.7 to 12.0 h by increasing the viscosity grade of HPMC from 0.1 to 100 K. Moreover, the tablet swelled and maintained a size comparable to a human pylorus diameter or more for at least 24 h. This GRDDS could apply to a broader range of drug candidates.

Supersaturation-Based Drug Delivery Systems: Strategy for Bioavailability Enhancement of Poorly Water-Soluble Drugs

At present, the majority of APIs synthesized today remain challenging tasks for formulation development. Many technologies are being utilized or explored for enhancing solubility, such as chemical modification, novel drug delivery systems (microemulsions, nanoparticles, liposomes, etc.), salt formation, and many more. One promising avenue attaining attention presently is supersaturated drug delivery systems. When exposed to gastrointestinal fluids, drug concentration exceeds equilibrium solubility and a supersaturation state is maintained long enough to be absorbed, enhancing bioavailability. In this review, the latest developments in supersaturated drug delivery systems are addressed in depth.

In Silico, In Vitro, and In Vivo Evaluation of Precipitation Inhibitors in Supersaturated Lipid-Based Formulations of Venetoclax

The concept of using precipitation inhibitors (PIs) to sustain supersaturation is well established for amorphous formulations but less in the case of lipid-based formulations (LBF). This study applied a systematic in silico–in vitro–in vivo approach to assess the merits of incorporating PIs in supersaturated LBFs (sLBF) using the model drug venetoclax. sLBFs containing hydroxypropyl methylcellulose (HPMC), hydroxypropyl methylcellulose acetate succinate (HPMCAS), polyvinylpyrrolidone (PVP), PVP-co-vinyl acetate (PVP/VA), Pluronic F108, and Eudragit EPO were assessed in silico calculating a drug–excipient mixing enthalpy, in vitro using a PI solvent shift test, and finally, bioavailability was assessed in vivo in landrace pigs. The estimation of pure interaction enthalpies of the drug and the excipient was deemed useful in determining the most promising PIs for venetoclax. The sLBF alone (i.e., no PI present) displayed a high initial drug concentration in the aqueous phase during in vitro screening. sLBF with Pluronic F108 displayed the highest venetoclax concentration in the aqueous phase and sLBF with Eudragit EPO the lowest. In vivo, the sLBF alone showed the highest bioavailability of 26.3 ± 14.2%. Interestingly, a trend toward a decreasing bioavailability was observed for sLBF containing PIs, with PVP/VA being significantly lower compared to sLBF alone. In conclusion, the ability of a sLBF to generate supersaturated concentrations of venetoclax in vitro was translated into increased absorption in vivo. While in silico and in vitro PI screening suggested benefits in terms of prolonged supersaturation, the addition of a PI did not increase in vivo bioavailability. The findings of this study are of particular relevance to pre-clinical drug development, where the high in vivo exposure of venetoclax was achieved using a sLBF approach, and despite the perceived risk of drug precipitation from a sLBF, including a PI may not be merited in all cases.

Exploring precipitation inhibitors to improve in vivo absorption of cinnarizine from supersaturated lipid-based drug delivery systems

Supersaturated lipid-based drug delivery systems are increasingly being explored as a bio-enabling formulation approach, particularly in preclinical evaluation of poorlywater-soluble drugs. While increasing the drug load through thermally-induced supersaturation resulted in enhanced in vivo exposure for some drugs, for others, such as cinnarizine, supersaturated lipid-based systems have not been found beneficial to increase the in vivo bioavailability. We hypothesized that incorporation of precipitation inhibitors to reduce drug precipitation may address this limitation. Therefore, pharmacokinetic profiles of cinnarizine supersaturated lipid-based drug delivery systems with or without precipitation inhibitors were compared. Five precipitation inhibitors were selected for investigation based on a high throughput screening of twenty-one excipients. In vivo results showed that addition of 5% precipitation inhibitors to long chain monoglyceride (LCM) or medium chain monoglyceride (MCM) formulations showed a general trend of increases in cinnarizine bioavailability, albeit only statistically significantly increased for Poloxamer 407 + LCM system (i.e. 2.7-fold increase in AUC_0-24h compared to LCM without precipitation inhibitors). It appeared that precipitation inhibitors mitigated the risk of in vivo precipitation of cinnarizine from sLBDDS and overall, bioavailability was comparable to that previously reported for cinnarizine after dosing of non-supersaturated lipid systems. In summary, for drugs which are prone to precipitation from supersaturated lipid-based drug delivery systems, such as cinnarizine, inclusion of precipitation inhibitors mitigates this risk and provides the opportunity to maximize exposure which is ideally suited in early efficacy and toxicology evaluation.

Current challenges and future perspectives in oral absorption research: An opinion of the UNGAP network

Although oral drug delivery is the preferred administration route and has been used for centuries, modern drug discovery and development pipelines challenge conventional formulation approaches and highlight the insufficient mechanistic understanding of processes critical to oral drug absorption. This review presents the opinion of UNGAP scientists on four key themes across the oral absorption landscape: (1) specific patient populations, (2) regional differences in the gastrointestinal tract, (3) advanced formulations and (4) food-drug interactions. The differences of oral absorption in pediatric and geriatric populations, the specific issues in colonic absorption, the formulation approaches for poorly water-soluble (small molecules) and poorly permeable (peptides, RNA etc.) drugs, as well as the vast realm of food effects, are some of the topics discussed in detail. The identified controversies and gaps in the current understanding of gastrointestinal absorption-related processes are used to create a roadmap for the future of oral drug absorption research.

Development of a Solid Supersaturable Micelle of Revaprazan for Improved Dissolution and Oral Bioavailability Using Box-Behnken Design

PURPOSE

To enhance the oral bioavailability of revaprazan (RVP), a novel solid, supersaturable micelle (SSuM) was developed.

METHODS

Surfactants and solid carriers were screened based on a solubility and a flowability test, respectively. Supersaturating agents, including Poloxamer 407 (P407), were screened. The SSuM was optimized using a Box-Behnken design with three independent variables, including Gelucire 44/14:Brij L4 (G44/BL4; X1) and the amounts of Florite PS-10 (FLO; X2) and Vivapur 105 (VP105; X3), and three response variables, ie, dissolution efficiency at 30 min (Y1), dissolution enhancing capacity (Y2), and Carr's index (Y3). The solid state property was evaluated, and a dissolution test was conducted. RVP, Revanex®, solid micelle (P407-free from the composition of SSuM), and SSuM were orally administrated to rats (RVP 20 mg equivalent/kg) for in vivo pharmacokinetic study.

RESULTS

G44 and BL4 showed great solubility, with a critical micelle concentration range of 119.2-333.0 μg/mL. P407 had an excellent supersaturating effect. FLO and VP105 were selected as solid carriers, with a critical solidifying ratio (g/mL) of 0.30 and 0.91, respectively. With optimized values of X1 (-0.41), X2 (0.31), and X3 (-0.78), RVP (200 mg)-containing SSuM consisting of G44 (253.8 mg), BL4 (106.2 mg), FLO (99.3 mg), VP105 (199.8 mg), and P407 (40 mg) was developed, resulting in Y1 (40.3%), Y2 (0.008), and Y3 (12.3%). RVP existed in an amorphous state in the optimized SSuM, and the SSuM formed a nanosized dispersion in the aqueous phase, with approximately 71.7% dissolution at 2 h. The optimized SSuM improved the relative bioavailability of RVP in rats by approximately 478%, 276%, and 161% compared to raw RVP, Revanex®, and solid micelle, respectively.

CONCLUSION

The optimized SSuM has great potential for the development of solidified formulations of poorly water-soluble drugs with improved oral absorption.

A mechanistic review on the dissolution phase behavior and supersaturation stabilization of amorphous solid dispersions

Amorphous solid dispersion (ASD) technology is an attractive formulation approach for poorly soluble drugs because of the supersaturated state acquired during its dissolution. The high thermodynamic activity of the supersaturated state of the drug is also a driver for the enhanced absorptive flux across a membrane. However, this advantage can easily be lost due to the inherent instability of supersaturation, causing drug precipitation. Stabilizing the supersaturated state during the dissolution of ASD for the relevant absorption time frame is a challenging area in formulation research. Stabilizing the supersaturated state by using polymeric excipients and understanding the phase behavior of drugs during dissolution are required for the optimal performance of ASD formulations. A number of confounding kinetic, formulation and physiological factors can influence the evolution of supersaturation and phase changes during dissolution of ASDs. The review highlights the complex nature of dissolution of ASDs and the need of biorelevant dissolution for proper risk assessment and optimizing formulation development.

Interaction with biliary and pancreatic fluids drives supersaturation and drug absorption from lipid-based formulations of low (saquinavir) and high (fenofibrate) permeability poorly soluble drugs

Drug absorption from lipid-based formulations (LBFs) in the gastrointestinal (GI) tract is the result of a series of processes, including formulation dispersion, interaction with biliary and pancreatic secretions, drug solubilisation and supersaturation, and finally intestinal permeability. Optimal formulation design is dependent on a good understanding of the limitations to, and drivers of, absorption, but for LBFs the complexity of these processes makes data interpretation complex. The current study has re-examined a previous in vitro digestion-in situ perfusion model to increase physiological relevance and has used this model to examine drug absorption from LBFs. The composition of rat bile and jejunal fluid was also characterised to identify in vivo-relevant conditions. Digestion was initiated using rat bile/pancreatic fluid and the formulation and digestive enzymes mixed immediately prior to entry into the jejunum (allowing dilution/digestion to occur at the absorptive site). These conditions were employed to study drug absorption from LBFs of high (fenofibrate, FFB) and low (saquinavir, SQV) permeability compounds. The impact of polymeric precipitation inhibitors (PPIs) was also evaluated. For FFB, supersaturation, initiated by formulation interaction with biliary/pancreatic fluids, appeared to drive absorption and the addition of the PPIs poly(glycidyl methacrylate) (PPGAE) and hydroxypropylmethyl cellulose (HPMC), reduced drug precipitation, increased FFB supersaturation and increased absorption from a Type IV LBF of FFB. For a Type IIIB LBF however, PPIs were ineffective at increasing absorption. The impact of PPIs on the absorption of a less permeable drug, SQV, was similarly evaluated and again drug absorption appeared to be related to the extent of supersaturation, although in this case PPI were unable to promote absorption. For both FFB and SQV, drug absorption patterns obtained with the in vitro digestion-in situ perfusion mode, correlated well with in vitro supersaturation data and in vivo drug exposure data from oral bioavailability studies. The data are consistent with a mode of drug absorption where rapid dilution of LBFs with biliary and pancreatic secretions at the absorptive site in the upper small intestine drives transient supersaturation, that supersaturation is a significant driver of drug absorption for both low and high permeability drugs, and that PPIs delay drug precipitation, enhance supersaturation and promote drug absorption in a drug and formulation specific manner.

Single-stranded β-1,3-1,6-glucan as a carrier for improved dissolution and membrane permeation of poorly water-soluble compounds

The ability of a water-soluble, single-stranded β-1,3/1,6-glucan (ssβ-glucan), recovered by hydrothermal treatment, to enhance the solubility and membrane permeability of poorly water-soluble compounds was examined. As a poorly water-soluble model compound, quercetin (QUE) was used. The aqueous solubility of spray-dried particles (SDPs) of QUE/ssβ-glucan was significantly enhanced compared with that of the untreated QUE powder and the physical mixture of QUE/ssβ-glucan. Fourier-transform infrared spectra and small-angle X-ray scattering suggested strong interactions between ssβ-glucan and QUE in the SDPs, which was attributable to QUE entrapment in the helical ssβ-glucan structure. The amount of QUE infused into Caco-2 cells from QUE/ssβ-glucan SDPs was 16-fold and 5-fold higher than the amount infused from untreated QUE powder and the physical mixture of QUE/ssβ-glucan, respectively. These results showed that water-soluble ssβ-glucan improved QUE dissolution and membrane permeability.

A composite nanocarrier to inhibit precipitation of the weakly basic drug in the gastrointestinal tract

For weakly basic drugs, the sharp decrease of drug solubility and the following drug precipitation after drugs transferring from the gastric fluid to the intestinal fluid in the gastrointestinal (GI) tract is a main reason for the poor oral bioavailability of drugs. Here, an anticoagulant dabigatran etexilate (DE) was used as a model drug, and a composite nanocarrier system of DE was developed to improve the drug dissolution by decreasing the drug leakage in the stomach and inhibiting the drug precipitation in the intestinal tract. With the encapsulation of drugs in nanocarriers, the precipitation percentage of DE in composite nanocarriers was 22.25 ± 3.88% in simulated intestinal fluid, which was far below that of the commercial formulation. Moreover, the relative bioavailability of DE-loaded composite nanocarriers (456.58%) was greatly enhanced and the peak of its activated partial thromboplastin time was also significantly prolonged (p < .01) compared with the commercial formulation, indicating that the anticoagulant effect of DE was effectively improved. Therefore, the designed composite nanocarrier system of DE presents great potentials in improving the therapeutic efficiency and expanding the clinical applications of poorly water-soluble weakly basic drugs.

Current Status of Supersaturable Self-Emulsifying Drug Delivery Systems

Self-emulsifying drug delivery systems (SEDDSs) are a vital strategy to enhance the bioavailability (BA) of formulations of poorly water-soluble compounds. However, these formulations have certain limitations, including in vivo drug precipitation, poor in vitro in vivo correlation due to a lack of predictive in vitro tests, issues in handling of liquid formulation, and physico-chemical instability of drug and/or vehicle components. To overcome these limitations, which restrict the potential usage of such systems, the supersaturable SEDDSs (su-SEDDSs) have gained attention based on the fact that the inclusion of precipitation inhibitors (PIs) within SEDDSs helps maintain drug supersaturation after dispersion and digestion in the gastrointestinal tract. This improves the BA of drugs and reduces the variability of exposure. In addition, the formulation of solid su-SEDDSs has helped to overcome disadvantages of liquid or capsule dosage form. This review article discusses, in detail, the current status of su-SEDDSs that overcome the limitations of conventional SEDDSs. It discusses the definition and range of su-SEDDSs, the principle mechanisms underlying precipitation inhibition and enhanced in vivo absorption, drug application cases, biorelevance in vitro digestion models, and the development of liquid su-SEDDSs to solid dosage forms. This review also describes the effects of various physiological factors and the potential interactions between PIs and lipid, lipase or lipid digested products on the in vivo performance of su-SEDDSs. In particular, several considerations relating to the properties of PIs are discussed from various perspectives.

Ionic Liquid Forms of the Antimalarial Lumefantrine in Combination with LFCS Type IIIB Lipid-Based Formulations Preferentially Increase Lipid Solubility, In Vitro Solubilization Behavior and In Vivo Exposure

Lipid based formulations (LBFs) are commonly employed to enhance the absorption of highly lipophilic, poorly water-soluble drugs. However, the utility of LBFs can be limited by low drug solubility in the formulation. Isolation of ionizable drugs as low melting, lipophilic salts or ionic liquids (ILs) provides one means to enhance drug solubility in LBFs. However, whether different ILs benefit from formulation in different LBFs is largely unknown. In the current studies, lumefantrine was isolated as a number of different lipophilic salt/ionic liquid forms and performance was assessed after formulation in a range of LBFs. The solubility of lumefantrine in LBF was enhanced 2- to 80-fold by isolation as the lumefantrine docusate IL when compared to lumefantrine free base. The increase in drug loading subsequently enhanced concentrations in the aqueous phase of model intestinal fluids during in vitro dispersion and digestion testing of the LBF. To assess in vivo performance, the systemic exposure of lumefantrine docusate after administration in Type II-MCF, IIIB-MCF, IIIB-LCF, and IV formulations was evaluated after oral administration to rats. In vivo exposure was compared to control lipid and aqueous suspension formulations of lumefantrine free base. Lumefantrine docusate in the Type IIIB-LCF showed significantly higher plasma exposure compared to all other formulations (up to 35-fold higher). The data suggest that isolation of a lipid-soluble IL, coupled with an appropriate formulation, is a viable means to increase drug dose in an oral formulation and to enhance exposure of lumefantrine in vivo.

Improving the drug load and in vitro performance of supersaturated self-nanoemulsifying drug delivery systems (super-SNEDDS) using polymeric precipitation inhibitors

In this study, the influence of the polymeric precipitation inhibitor (PPI) PVP/VA 64 (polyvinylpyrrolidone-co-vinyl acetate) on the physical stability and in vitro performance of supersaturated self-nanoemulsifying drug delivery systems (super-SNEDDS) containing the model drug simvastatin (SIM) was investigated. A heating-cooling cycle was employed to dissolve (i) the drug in the SNEDDS preconcentrate, generating super-SNEDDS, or (ii) the drug and PPI generating PPI super-SNEDDS, both containing drug loads of 200% and 250% (with regard to the equilibrium solubility of SIM in the blank SNEDDS). PPI super-SNEDDS were prepared at PPI concentrations of 1%, 10% and 20% (w/w), respectively. The formulations were characterized using polarized light microscopy, dynamic light scattering, rheological profiling and dynamic in vitro lipolysis. The physical stability of PPI super-SNEDDS correlated with an increase in viscosity due to the additionally dissolved PVP/VA 64. PPI super-SNEDDS with drug loads of 200% and 250% containing 20% (w/w) PPI showed no drug recrystallization after more than 6 months of storage at room temperature, whereas PPI-free super-SNEDDS (250% drug load) recrystallized within two hours after equilibration to room temperature. All formulations formed nanosized droplets after emulsification in Milli-Q water. The droplet size was not affected by the PPI, but increased slightly with increasing drug load (z-average of 47.3 ± 0.4 nm for SNEDDS with 200% drug load and 55.6 ± 1.3 nm for SNEDDS with 250% drug load). PPI super-SNEDDS with a drug load of 200% containing 20% (w/w) PVP/VA 64 showed an improved performance during dynamic in vitro lipolysis, maintaining a 2.5-fold higher degree of supersaturation after 15 min of digestion compared to PPI-free super-SNEDDS of the same drug load. In conclusion, the study demonstrated the feasibility of stabilizing higher drug loads and improving the in vitro performance of super-SNEDDS by incorporating PVP/VA 64 into the preconcentrate.

Interplay of Supersaturation and Solubilization: Lack of Correlation between Concentration-Based Supersaturation Measurements and Membrane Transport Rates in Simulated and Aspirated Human Fluids

Supersaturating formulations are increasingly being used to improve the absorption of orally administered poorly water-soluble drugs. To better predict outcomes in vivo, we must be able to accurately determine the degree of supersaturation in complex media designed to provide a surrogate for the gastrointestinal environment. Herein, we demonstrate that relying on measurements based on consideration of the total dissolved concentration leads to underestimation of supersaturation and consequently membrane transport rates. Crystalline and amorphous solubilities of two compounds, atazanavir and posaconazole, were evaluated in six different media. Concurrently, diffusive flux measurements were performed in a side-by-side diffusion cell to determine the activity-based supersaturation by evaluating membrane transport rates at the crystalline and amorphous solubilities. Solubility values were found to vary in each medium because of different solubilization capacities. Concentration-based supersaturation ratios were also found to vary for the different media. Activity-based measurements, however, were largely independent of the medium, leading to relatively constant values for the estimated supersaturation. These findings have important consequences for modeling and prediction of supersaturation impact on the absorption rate as well as for better defining the thermodynamic driving force for crystallization in complex media.

Polymeric precipitation inhibitor as an effective trigger to convert supersaturated into supersaturable state in vivo

The supersaturated state of the drug in vivo is thermodynamically unstable resulting in a delayed response and reduced efficacy. The use of polymeric precipitation inhibitor (PPI) has been demonstrated as an effective trigger for the conversion of supersaturated state to supersaturable state for improving solubilization, thermodynamic maintenance of drug concentration and oral absorption of poorly water-soluble compounds. PPI retards drug precipitation and provides a kinetically stabilized supersaturation state for an extended period in gastric and intestinal fluids. However, the selection of appropriate PPI and understanding its mechanism is a challenge for formulating a stable pharmaceutical formulation. The present review is aimed at understanding the intricacies of selecting PPIs and their applications in pharmaceutical formulations.

A carbohydrate polymer is a critical variable in the formulation of drug nanocrystals: a case study of idebenone

Objective: Stabilizers, especially carbohydrate polymers, have been shown to be necessary for the stabilization of drug nanocrystals. However, the impacts of select stabilizers on the in vitro and in vivo efficacy of therapeutics have rarely been reported. The aim of this study was to evaluate the importance of stabilizers in the formulation of drug nanocrystals.Research design and methods: Idebenone nanocrystals (IDBNC) stabilized by various stabilizers were formulated using a milling method. The in vitro dissolution profiles in water and in situ absoprtion were compared. Finally, an in vivo pharmacokinetic study was performed.Results: The IDBNC profiles were found to have acceptable sizes and similar morphology and crystallinity. The dissolution profiles of IDBNC stabilized by different stabilizers were notably different, indicating the critical influence of stabilizers on the release rate of IDB. The Soluplus-stabilized IDBNC (IDBNC_{400 nm}/Soluplus) achieved better absorption than HPMC stabilized IDBNC (IDBNC_{400 nm}/HPMC). The pharmacokinetic study demonstrated that Soluplus-stabilized IDBNC had preferable kinetics, with an AUC_0-24h of IDBNC_{400 nm}/Soluplus (3.08-fold relative to IDB suspension), compared to IDBNC_{400 nm}/HPMC (1.88-fold).Conclusions: Choice of stabilizer plays an important role in the formulation of IDBNC. We anticipate that the role of stabilizers in the pharmacokinetic disposition of IDBNC has significant implications for a wide range of other drug crystal formulations.

Successful oral delivery of poorly water-soluble drugs both depends on the intraluminal behavior of drugs and of appropriate advanced drug delivery systems

Poorly water-soluble drugs continue to be a problematic, yet important class of pharmaceutical compounds for treatment of a wide range of diseases. Their prevalence in discovery is still high, and their development is usually limited by our lack of a complete understanding of how the complex chemical, physiological and biochemical processes that occur between administration and absorption individually and together impact on bioavailability. This review defines the challenge presented by these drugs, outlines contemporary strategies to solve this challenge, and consequent in silico and in vitro evaluation of the delivery technologies for poorly water-soluble drugs. The next steps and unmet needs are proposed to present a roadmap for future studies for the field to consider enabling progress in delivery of poorly water-soluble compounds.

An update on polymer-lipid hybrid systems for improving oral drug delivery

INTRODUCTION

A promising approach that has recently emerged to overcome the complex biobarriers and interrelated challenges associated with oral drug absorption is to combine the benefits of polymeric and lipid-based nanocarriers within one hybrid system. This multifaceted formulation strategy has given rise to a plethora of polymer-lipid hybrid (PLH) systems with varying nanostructures and biological activities, all of which have demonstrated the ability to improve the biopharmaceutical performance of a wide range of challenging therapeutics.

AREAS COVERED

The multitude of polymers that can be combined with lipids to exert a synergistic effect for oral drug delivery have been identified, reviewed and critically evaluated. Specific focus is attributed to preclinical studies performed within the past 5 years that have elucidated the role and mechanism of the polymer phase in altering the oral absorption of encapsulated therapeutics.

EXPERT OPINION

The potential of PLH systems has been clearly identified; however, improved understanding of the structure-activity relationship between PLH systems and oral absorption is fundamental for translating this promising delivery approach into a clinically relevant formulation. Advancing research within this field to identify optimal polymer, lipid combinations and engineering conditions for specific therapeutics are therefore encouraged.

Drug supersaturation during formulation digestion, including real-time analytical approaches

Self-emulsifying and other lipid-based drug delivery systems have drawn considerable interest from pharmaceutical scientists for managing oral delivery of poorly water-soluble compounds. Following administration, self-emulsifying systems exhibit complex aqueous dispersion and digestion in the gastro-intestinal tract. These processes generally result in drug supersaturation, which leads to enhanced absorption or the high drug concentrations may cause precipitation with erratic and variable oral bioavailability. This review briefly outlines drug supersaturation obtained from self-emulsifying and other lipid-based formulations; recent advancements of in vitro lipolysis testing are also discussed. Further, a main focus is mechanisms by which supersaturation is triggered from gastro-intestinal processes, as well as analytical techniques that are promising from a research and development perspective. Comparatively simple approaches are presented together with more sophisticated process analytics to enable direct examination of kinetic changes. The analytical methods together with their sensor probes are discussed in detail to clarify opportunities as well as technical limitations. Some of the more sophisticated methods, including those based on synchrotron radiation, are primarily research oriented despite interesting experimental findings from an industrial viewpoint. The availability of kinetic data further opens the door to mathematical modeling of supersaturation and precipitation versus permeation, which lays the groundwork for better in vitro to in vivo correlations as well as for physiologically-based modeling of lipid-based systems.

Lipolysis-Permeation Setup for Simultaneous Study of Digestion and Absorption in Vitro

Lipid-based formulations (LBFs) are a delivery strategy to enhance intestinal absorption of poorly water-soluble drugs. LBF performance is typically evaluated by in vitro lipolysis studies, but these do not accurately predict the in vivo performance. One possible reason is the absence of an absorptive membrane driving sink conditions in the serosal compartment. To explore the impact of absorption under sink conditions on the performance evaluation, we developed a lipolysis-permeation setup that allows simultaneous investigation of intestinal digestion of an LBF and drug absorption. The setup consists of two chambers, an upper one for digestion (luminal), and a lower, receiving one (serosal), separated by a Caco-2 monolayer. Digestions were performed with immobilized lipase, instead of the pancreatic extract typically used during lipolysis, since the latter has proven incompatible with Caco-2 cells. Danazol-loaded LBFs were used to develop the setup, and fenofibrate-loaded LBFs were used to establish an in vitro in vivo correlation. As in regular lipolysis studies, our setup allows for the evaluation of (i) the extent of digestion and (ii) drug distribution in different phases present during lipolysis of drug-loaded LBFs (i.e., oil, aqueous, and solid phase). In addition, our setup can determine drug permeation across Caco-2 monolayers and hence, the absorptive flux of the compound. The presence of the absorptive monolayer and sink conditions tended to reduce aqueous drug concentrations and supersaturation in the digestion chamber. The drug transfer across the Caco-2 membrane accurately reflected in vivo drug exposure upon administration of three different LBFs loaded with fenofibrate, where the traditional lipolysis setup failed to predict in vivo performance. As the new setup reflects the dynamic processes occurring in the gastrointestinal tract, it is a valuable tool that can be used in the development of LBFs prior to in vivo studies.

A Nonionic Polyethylene Oxide (PEO) Surfactant Model: Experimental and Molecular Dynamics Studies of Kolliphor EL

Polyethoxylated, nonionic surfactants are important constituents of many drug formulations, including lipid-based formulations. In an effort to better understand the behavior of formulation excipients at the molecular level, we have developed molecular dynamics (MD) models for the widely used surfactant Kolliphor EL (KOL), a triricinoleate ester of ethoxylated glycerol. In this work, we have developed models based on a single, representative molecular component modeled with 2 force field variations based on the GROMOS 53A6_DBW and 2016H66 force field parameters for polyethoxylate chains. To compare the computational models to experimental measurements, we investigated the phase behavior of KOL using nephelometry, dynamic light scattering, cross-polarized microscopy, small-angle X-ray scattering, and cryogenic transmission electron microscopy. The potential for digestion of KOL was also evaluated using an in vitro digestion experiment. We found that the size and spherical morphology of the KOL colloids at low concentrations was reproduced by the MD models as well as the growing interactions between the aggregates to from rod-like structures at high concentrations. We believe that this model reproduces the phase behavior of KOL relevant to drug absorption and that it can be used in whole formulation simulations to accelerate the formulation development.

Enhancing the Oral Absorption of Kinase Inhibitors Using Lipophilic Salts and Lipid-Based Formulations

The absolute bioavailability of many small molecule kinase inhibitors (smKIs) is low. The reasons for low bioavailability are multifaceted and include constraints due to first pass metabolism and poor absorption. For smKIs where absorption limits oral bioavailability, low aqueous solubility and high lipophilicity, often in combination with high-dose requirements have been implicated in low and variable absorption, food-effects, and absorption-related drug-drug interactions. The current study has evaluated whether preparation of smKIs as lipophilic salts/ionic liquids in combination with coadministration with lipid-based formulations is able to enhance absorption for examples of this compound class. Lipophilic (docusate) salt forms of erlotinib, gefitinib, ceritinib, and cabozantinib (as example smKIs demonstrating low aqueous solubility and high lipophilicity) were prepared and isolated as workable powder solids. In each case, the lipophilic salt exhibited high and significantly enhanced solubility in lipidic excipients (>100 mg/g) when compared to the free base or commercial salt form. Isolation as the lipophilic salt facilitated smKI loading in model lipid-based formulations at high concentration, increased in vitro solubilization at gastric and intestinal pH and in some cases increased oral absorption (∼2-fold for cabozantinib formulations in rats). Application of a lipophilic salt approach can therefore facilitate the use of lipid-based formulations for examples of the smKI compound class where low solubility limits absorption and is a risk factor for increased variability due to food-effects.