Indomethacin-Kollidon VA64 Extrudates: A Mechanistic Study of pH-Dependent Controlled Release

Drug Release from Lipid Microparticles-Insights into Drug Incorporation and the Influence of Physiological Factors

The aim of this study was to assess the impact of physiological factors, namely tear fluid and lysozyme enzyme, as well as surfactant polysorbate, on the release profile from solid lipid microparticles (SLM), in the form of dispersion intended for ocular application. Indomethacin (Ind) was used as a model drug substance and a release study was performed by applying the dialysis bag method. Conducting release studies taking into account physiological factors is expected to improve development and screening studies, as well as support the regulatory assessment of this multi-compartment lipid dosage form. The effect of the lysozyme was directly related to its effect on lipid microparticles, as it occurred only in their presence (no effect on the solubility of Ind). Polysorbate also turned out to be an important factor interacting with the SLM surface, which determined the release of Ind from SLM. However, in study models without tear fluid or lysozyme, the release of Ind did not exceed 60% within 96 h. Ultimately, only the simultaneous application of artificial tear fluid, lysozyme, and polysorbate allowed for the release of 100% of Ind through the SLM dispersion. The examination of the residues after the release studies indicated the possibility of releasing 100% of Ind from SLM without complete degradation of the microparticles' matrix. The incubation of SLM with tear fluid confirmed a similar influence of physiological factors contained in tear fluid on the surface structure of SLM as that observed during the in vitro studies.

Impact of polymer chemistry on critical quality attributes of selective laser sintering 3D printed solid oral dosage forms

The aim of this study is to investigate the influence of polymer chemistry on the properties of oral dosage forms produced using selective laser sintering (SLS). The dosage forms were printed using different grades of polyvinyl alcohol or copovidone in combination with indomethacin as the active pharmaceutical ingredient. The properties of the printed structures were assessed according to European Pharmacopoeia guidelines at different printing temperatures and laser scanning speeds in order to determine the suitable printing parameters. The results of the study indicate that the chemical properties of the polymers, such as dynamic viscosity, degree of hydrolyzation, and molecular weight, have significant impact on drug release and kinetics. Drug release rate and supersaturation can be modulated by selecting the appropriate polymer type. Furthermore, the physical properties of the dosage forms printed under the same settings are influenced by the selected polymer type, which determines the ideal manufacturing settings. This study demonstrates how the chemical properties of the polymer can determine the appropriate choice of manufacturing settings and the final properties of oral dosage forms produced using SLS.

Effect of Buffer pH and Concentration on the Dissolution Rates of Sodium Indomethacin-Copovidone and Indomethacin-Copovidone Amorphous Solid Dispersions

The incorporation of counterions into amorphous solid dispersions (ASDs) has been proven to be effective for improving the dissolution rates of ionizable drugs in ASDs. In this work, the effect of dissolution buffer pH and concentration on the dissolution rate of indomethacin-copovidone 40:60 (IMC-PVPVA, w/w) ASD with or without incorporated sodium hydroxide (NaOH) was studied by surface area-normalized dissolution to provide further mechanistic understanding of this phenomenon. Buffer pH from 4.7 to 7.2 and concentration from 20 to 100 mM at pH 5.5 were investigated. As the buffer pH decreased, the IMC dissolution rate from both ASDs decreased. Compared to IMC-PVPVA ASD, the dissolution rate decrease from IMCNa-PVPVA ASD was more resistant to the decrease of buffer pH. In contrast, while buffer concentration had a negligible impact on the IMC dissolution rate from IMC-PVPVA ASD, the increase of buffer concentration significantly reduced the IMC dissolution rate from IMCNa-PVPVA ASD. Surrogate evaluation of microenvironment pH modification by the dissolution of IMCNa-PVPVA ASD demonstrated the successful elevation of buffer microenvironment pH and the suppression of such pH elevation by the increase of buffer concentration. These results are consistent with the hypothesis that the dissolution rate enhancement by the incorporation of counterions originates from the enhanced drug solubility by ionization and the modification of diffusion layer pH in favor of drug dissolution. At the studied drug loading (∼40%), relatively congruent release between IMC and PVPVA was observed when IMC was ionized in ASD or in solution, highlighting the importance of studying the ionization effect on the congruent release of ASDs, especially when drug ionization is expected in vivo. Overall, this work further supports the application of incorporating counterions into ASDs for improving the dissolution rates of ionizable drugs when enabling formulation development is needed.

The Influence of Gastrointestinal Biomolecules on Solid-State Transformations in Pharmaceutical Particulates

Adsorption of gut relevant biomolecules onto particles after oral administration of solid oral dosage forms is expected to form a "gastrointestinal corona", which could influence solution-mediated solid-state transformations on exposure of drug particles to gastrointestinal fluids. Low-frequency Raman (LFR) spectroscopy was used in this study to investigate in situ solid-state phase transformations under biorelevant temperature and pH conditions along with the presence of biomolecules. Melt-quenched amorphous indomethacin was used as a model solid particulate, and its solid-state behavior was evaluated at 37 °C and pH 1.2-6.8 with or without the presence of typical bile salt/phospholipid mixtures emulating fed-state conditions. Overall, a change in the solid-state transformation pathway from amorphous to crystalline drug was observed, where an intermediate ε-form that initially formed at pH 6.8 was suppressed by the addition of endogenous gastrointestinal biomolecules. These solid-state changes were corroborated using time-resolved synchrotron small- and wide-angle X-ray scattering (SAXS/WAXS). Additionally, the bile salt and phospholipid mixture partly prevented the otherwise strong aggregation between drug particles at more acidic conditions (pH ≤ 4.5) and helped to shift the balance against the intrinsic hydrophobicity of indomethacin as well as the plasticization effect brought about by the physiological temperature (i.e., the stickiness arising from the supercooled liquid state at 37 °C). The overall results highlight the importance of evaluating the impact that endogenous biomolecules may have on the solid-state characteristics of drug molecules in dissolution media, where analytical tools such as LFR spectroscopy can serve as an attractive avenue for accessing time-resolved solid-state information on time-scales that are difficult to achieve with other techniques such as X-ray diffraction.

Biorelevant Dissolution Method Considerations for the Appropriate Evaluation of Amorphous Solid Dispersions: are Two Stages Necessary?

Biorelevant dissolution testing has been widely used to better understand a drug or formulation's behavior in the human gastrointestinal (GI) tract. The successful evaluation of biorelevant dissolution behavior requires recognizing the importance of utilizing suitable biorelevant media in conjunction with an appropriate dissolution method, especially for supersaturating drug delivery systems, such as amorphous solid dispersions (ASDs). However, most conventional biorelevant dissolution testing methods are not able to accurately reflect the dissolution, supersaturation, and precipitation tendencies of a drug or formulation, which could misinform ASD formulation screening and optimization. In this study, we developed a single compartment 2-stage pH-shift dissolution testing method to simulate the changes in pH, media composition, and transit time in the GI tract, and results were compared against the conventional single compartment 1-stage dissolution method. Nine model drugs were selected based on their ionization properties (i.e. acid, base or neutral) and precipitation tendency (i.e. moderate or slow crystallizer). The dissolution results confirmed that 2-stage pH-shift dissolution is the preferred biorelevant dissolution method to assess non-ionized weak base (nifedipine) and neutral (griseofulvin) compounds exhibiting a moderate precipitation rate from solution when formulated as ASDs. Finally, we designed a flowchart guidance for the appropriate biorelevant dissolution performance characterization of different categories of ASD formulations.

Personalised Paediatric Chewable Ibuprofen Tablets Fabricated Using 3D Micro-extrusion Printing Technology

Three-dimensional (3D) printing is becoming an attractive technology for the design and development of personalized paediatric dosage forms with improved palatability. In this work micro-extrusion based printing was implemented for the fabrication of chewable paediatric ibuprofen (IBU) tablets by assessing a range of front runner polymers in taste masking. Due to the drug-polymer miscibility and the IBU plasticization effect, micro-extrusion was proved to be an ideal technology for processing the drug/polymer powder blends for the printing of paediatric dosage forms. The printed tablets presented high printing quality with reproducible layer thickness and a smooth surface. Due to the drug-polymer interactions induced during printing processing, IBU was found to form a glass solution confirmed by differential calorimetry (DSC) while H-bonding interactions were identified by confocal Raman mapping. IBU was also found to be uniformly distributed within the polymer matrices at molecular level. The tablet palatability was assessed by panellists and revealed excellent taste masking of the IBU's bitter taste. Overall micro-extrusion demonstrated promising processing capabilities of powder blends for rapid printing and development of personalised dosage forms.

Study of Physico-Chemical Properties and Morphology of Phospholipid Composition of Indomethacin

Nonsteroidal anti-inflammatory drugs (NSAIDs), inhibitors of cyclooxygenase-2, an enzyme involved in the formation of anti-inflammatory prostaglandin PGE2, are the most common treatment for chronic inflammatory diseases, such as, for example, arthritis. One of the most commonly used drugs of this class is indomethacin, a derivative of indolylacetic acid. In this work, we studied the physicochemical properties of the phospholipid composition of indomethacin obtained earlier (codenamed “Indolip”) and the effect of freeze drying on its parameters. It was shown that the properties such as particle size, light transmission, phospholipid oxidation index did not change significantly, which indicated the stability of the drug after lyophilization. Measurement of the spectra of small-angle neutron scattering has shown that morphologically, Indolip is a vesicle whose radius is five times greater than the value of the bilayer thickness.

Hybrid Nanobeads for Oral Indomethacin Delivery

The oral administration of the anti-inflammatory indomethacin (INDO) causes severe gastrointestinal side effects, which are intensified in chronic inflammatory conditions when a continuous treatment is mandatory. The development of hybrid delivery systems associates the benefits of different (nano) carriers in a single system, designed to improve the efficacy and/or minimize the toxicity of drugs. This work describes the preparation of hybrid nanobeads composed of nanostructured lipid carriers (NLC) loading INDO (2%; w/v) and chitosan, coated by xanthan. NLC formulations were monitored in a long-term stability study (25 °C). After one year, they showed suitable physicochemical properties (size < 250 nm, polydispersity < 0.2, zeta potential of −30 mV and spherical morphology) and an INDO encapsulation efficiency of 99%. The hybrid (lipid-biopolymers) nanobeads exhibited excellent compatibility between the biomaterials, as revealed by structural and thermodynamic properties, monodisperse size distribution, desirable in vitro water uptake and prolonged in vitro INDO release (26 h). The in vivo safety of hybrid nanobeads was confirmed by the chicken embryo (CE) toxicity test, considering the embryos viability, weights of CE and annexes and changes in the biochemical markers. The results point out a safe gastro-resistant pharmaceutical form for further efficacy assays.

Effect of Counterions on Dissolution of Amorphous Solid Dispersions Studied by Surface Area Normalized Dissolution

Solubility enhancement has become a common requirement for formulation development to deliver poorly water soluble drugs. Amorphous solid dispersions (ASDs) and salt formation have been two successful strategies, yet there are opportunities for further development. For ASDs, drug-polymer phase separation may occur at high drug loadings during dissolution, limiting the increase of drug loadings in ASD formulations. For salt formation, a salt form with high crystallinity and sufficient solid-state stability is required for solid dosage form development. This work studied the effect of counterions on the dissolution performance of ASDs. Surface area normalized dissolution or intrinsic dissolution methodology was employed to eliminate the effect of particle size and provide a quantitative comparison of the counterion effect on the intrinsic dissolution rate. Using indomethacin (IMC)-poly(vinylpyrrolidone-co-vinyl acetate) ASD as a model system, the effect of different bases incorporated into the ASD during preparation, the molar ratios between the base and IMC, and the drug loadings in the ASD were systematically studied. Strong bases capable of ionizing IMC significantly enhanced drug dissolution, while a weak base did not. A physical mixture of a strong base and the ASD also enhanced the dissolution rate, but the effect was less pronounced. At different base to IMC molar ratios, dissolution enhancement increased with the base to IMC ratio. At different drug loadings, without a base, the IMC dissolution rate decreased with the increase of drug loading. After incorporating a strong base, it increased with the increase of drug loading. The observations from this study were thought to be related to both the ionization of IMC in ASDs and the increase of microenvironment pH by the incorporated bases. With the significant enhancement of the drug dissolution rate, our work provides a promising approach of overcoming the dissolution limitation of ASD formulations at high drug loadings.

Bioavailability Improvement of Carbamazepine via Oral Administration of Modified-Release Amorphous Solid Dispersions in Rats

The purpose of this study was to improve the bioavailability of carbamazepine (CBZ), a poorly water-soluble antiepileptic drug, via modified-release amorphous solid dispersions (mr-ASD) by a thin film freezing (TFF) process. Three types of CBZ-mr-ASD with immediate-, delayed-, and controlled-release properties were successfully prepared with HPMC E3 (hydrophilic), L100-55 (enteric), and cellulose acetate (CA, lipophilic), defined as CBZ-ir-ASD, CBZ-dr-ASD, and CBZ-cr-ASD, respectively. A dry granulation method was used to prepare CBZ-mr-ASD capsule formulations. Various characterization techniques were applied to evaluate the physicochemical properties of CBZ-mr-ASD and the related capsules. The drug remained in an amorphous state when encapsulated within CBZ-mr-ASD, and the capsule formulation progress did not affect the performance of the dispersions. In dissolution tests, the preparations and the corresponding dosage forms similarly showed typical immediate-, delayed-, and controlled-release properties depending on the solubility of the polymers. Moreover, single-dose 24 h pharmacokinetic studies in rats indicated that CBZ-mr-ASD significantly enhanced the oral absorption of CBZ compared to that of crude CBZ. Increased oral absorption of CBZ was observed, especially in the CBZ-dr-ASD formulation, which showed a better pharmacokinetic profile than that of crude CBZ with 2.63- and 3.17-fold improved bioavailability of the drug and its main active metabolite carbamazepine 10,11-epoxide (CBZ-E).

Vacuum Compression Molding as a Screening Tool to Investigate Carrier Suitability for Hot-Melt Extrusion Formulations

Hot-melt extrusion (HME) is the most preferred and effective method for manufacturing amorphous solid dispersions at production scale, but it consumes large amounts of samples when used for formulation development. Herein, we show a novel approach to screen the polymers by overcoming the disadvantage of conventional HME screening by using a minimum quantity of active pharmaceutical ingredient (API). Vacuum Compression Molding (VCM) is a fusion-based method to form solid specimens starting from powders. This study aimed to investigate the processability of VCM for the creation of amorphous formulations and to compare its results with HME-processed formulations. Mixtures of indomethacin (IND) with drug carriers (Parteck^® MXP, Soluplus^®, Kollidon^® VA 64, Eudragit^® EPO) were processed using VCM and extrusion technology. Thermal characterization was performed using differential scanning calorimetry, and the solid-state was analyzed via X-ray powder diffraction. Dissolution studies in the simulated gastric fluid were performed to evaluate the drug release. Both technologies showed similar results proving the effectiveness of VCM as a screening tool for HME-based formulations.

Aqueous Dissolution and Dispersion Behavior of Polyvinylpyrrolidone Vinyl Acetate-based Amorphous Solid Dispersion of Ritonavir Prepared by Hot-Melt Extrusion with and without Added Surfactants

In this study, the lack of complete drug release from amorphous solid dispersions (ASDs), as observed in most published reports, was investigated. ASDs with 20% ritonavir were prepared by HME using polyvinylpyrrolidone vinyl acetate (PVPVA) alone and in combination with 10% poloxamer 407 or Span 20 as carriers. It was established by the film casting technique that ritonavir was molecularly dispersed in formulations, and accelerated stability testing confirmed that extrudates were physically stable. Dissolution of ASDs (100-mg ritonavir equivalent) was performed in 250 mL 0.01 N HCl (pH 2), pH 6.8 phosphate buffer and FeSSIF-V2. Drug concentrations were measured by filtration through 0.45-μm pores and in unfiltered media; the latter gave total amounts of drug present in dissolution media, both as solution and dispersion. Because of low solubility, ritonavir did not dissolve completely in aqueous media. Rather, it formed supersaturated solutions, and the excess drug dispersed in the oily amorphous form with low particle sizes that could crystallize with time. Due to higher drug solubility, the dissolved drug in FeSSIF-V2 was much higher than that in the phosphate buffer. Complete drug release could be observed by accounting for drug both in solution and as phase-separated dispersion. Thus, the present study provides a complete picture of in vitro drug dissolution and dispersion from ASDs.

The Effect of Cooling on the Degree of Crystallinity, Solid-State Properties, and Dissolution Rate of Multi-Component Hot-Melt Extruded Solid Dispersions

: The effect of cooling on the degree of crystallinity, solid-state and dissolution properties of multi-component hot-melt extruded solid dispersions [SD] is of great interest for the successful formulation of amorphous SDs and is an area that is unreported, especially in the context of improving the stability of these specific systems. The thermal solid-state properties, degree of crystallinity, drug-polymer interactions, solubility and physical stability over time were investigated. X-ray powder diffraction [XRPD] and hyper differential scanning calorimetry [DSC] confirmed that indomethacin [INM] was converted to the amorphous state; however, the addition of poloxamer 407 [P407] had a significant effect on the degree of crystallinity and the solubility of the SD formulations. Spectroscopy studies identified the mechanism of interaction and solubility studies, showing a higher dissolution rate compared to amorphous and pure INM in pH 1.2 with a kinetic solubility of 20.63 µg/mL and 34.7 µg/mL after 3 and 24 h. XRPD confirmed that INM remained amorphous after 5 months stability testing in solid solutions with Poly(vinylpyrrolidone-co-vinyl acetate) [PVP VA64] and Plasdone S-630 [PL-S630]. Although cooling had a significant effect on the degree of crystallinity and on solubility of INM, the cooling method used did not have any significant effect on the amorphous stability of INM over time.

Surface Stabilization and Dissolution Rate Improvement of Amorphous Compacts with Thin Polymer Coatings: Can We Have It All?

The distinction between surface and bulk crystallization of amorphous pharmaceuticals, as well as the importance of surface crystallization for pharmaceutical performance, is becoming increasingly evident. An emerging strategy in stabilizing the amorphous drug form is to utilize thin coatings at the surface. While the physical stability of systems coated with pharmaceutical polymers has recently been studied, the effect on dissolution performance as a function of storage time, as a further necessary step toward the success of these formulations, has not been previously studied. Furthermore, the effect of coating thickness has not been elucidated. This study investigated the effect of these polymer-coating parameters on the interplay between amorphous surface crystallization and drug dissolution for the first time. The study utilized simple tablet-like coated dosage forms, comprising a continuous amorphous drug core and thin polymer coating (hundreds of nanometers to a micrometer thick). Monitoring included analysis of both the solid-state of the model drug (with SEM, XRD, and ATR FTIR spectroscopy) and dissolution performance (and associated morphology and solid-state changes) after different storage times. Stabilization of the amorphous form (dependent on the coating thickness) and maintenance of early-stage intrinsic dissolution rates characteristic for the unaged amorphous drug were achieved. However, dissolution in the latter stages was likely inhibited by the presence of a polymer at the surface. Overall, this study introduced a versatile coated system for studying the dissolution of thin-coated amorphous dosage forms suitable for different drugs and coating agents. It demonstrated the importance of multiple factors that need to be taken into consideration when aiming to achieve both physical stability and improved release during the shelf life of amorphous formulations.

Formation of Indomethacin-Saccharin Cocrystals during Wet Granulation: Role of Polymeric Excipients

Formulation of a cocrystal into a solid pharmaceutical dosage form entails numerous processing steps during which there is risk of dissociation. In an effort to reduce the number of unit operations, we have attempted the in situ formation of an indomethacin-saccharin (INDSAC) cocrystal during high-shear wet granulation (HSWG). HSWG of IND (poorly water-soluble drug) and SAC (coformer), with polymers (granulating agents), was carried out using ethanol as the granulation liquid and yielded INDSAC cocrystal granules. Therefore, cocrystal formation and granulation were simultaneously accomplished. Our objectives were to (i) evaluate the influence of polymers on cocrystal formation kinetics during wet granulation and (ii) mechanistically understand the role of polymers in facilitating the cocrystal formation. Polyvinylpyrrolidone (PVP), hydroxypropyl cellulose (HPC), and polyethylene oxide (PEO) were chosen to investigate the influence of soluble polymers. The cocrystal formation kinetics was influenced by the polymer (PVP < HPC < PEO) and its concentration. The interaction of the polymer with cocrystal components inhibited the cocrystal formation. Complete cocrystal formation was observed in the presence of PEO, a polymer which does not interact with IND and SAC.

Micro-Injection Moulding of Poly(vinylpyrrolidone-vinyl acetate) Binary and Ternary Amorphous Solid Dispersions

Micro-injection moulding (µIM) was used for the production of enteric tablets of plasticised and unplasticised solid dispersions of poly(vinylpyrrolidone-vinyl acetate) (PVPVA), and the effect of the mechanical and thermal treatment on the properties of the dispersions was investigated. The physical state of the systems showed to be unaltered by the µIM step, maintaining the drug in the amorphous state. The dissolution profile of the tablets showed a slower dissolution rate due to the lower surface to volume ratio compared to the extruded strands. The lack of solubility of the doses in the acidic medium as a consequence of the acidity of indomethacin (IND) was observed. However, in neutral pH the drug dissolution showed slower rates without affecting the dissolution extent, showing a potential application for the development of controlled release doses. Overall, the production of tablets of amorphous solid dispersions (ASD), coupling hot-melt extrusion (HME) and µIM, proved to be a successful approach towards a continuous automated manufacturing process to improve the aqueous solubility of poorly water-soluble drugs.

Understanding Dissolution and Crystallization with Imaging: A Surface Point of View

The tendency for crystallization during storage and administration is the most considerable hurdle for poorly water-soluble drugs formulated in the amorphous form. There is a need to better detect often subtle and complex surface crystallization phenomena and understand their influence on the critical quality attribute of dissolution. In this study, the interplay between surface crystallization of the amorphous form during storage and dissolution testing, and its influence on dissolution behavior, is analyzed for the first time with multimodal nonlinear optical imaging (coherent anti-Stokes Raman scattering (CARS) and sum frequency generation (SFG)). Complementary analyses are provided with scanning electron microscopy, X-ray diffraction and infrared and Raman spectroscopies. Amorphous indomethacin tablets were prepared and subjected to two different storage conditions (30 °C/23% RH and 30 °C/75% RH) for various durations and then dissolution testing using a channel flow-through device. Trace levels of surface crystallinity previously imaged with nonlinear optics after 1 or 2 days of storage did not significantly decrease dissolution and supersaturation compared to the freshly prepared amorphous tablets while more extensive crystallization after longer storage times did. Multimodal nonlinear optical imaging of the tablet surfaces after 15 min of dissolution revealed complex crystallization behavior that was affected by both storage condition and time, with up to four crystalline polymorphs simultaneously observed. In addition to the well-known α- and γ-forms, the less reported metastable ε- and η-forms were also observed, with the ε-form being widely observed in samples that had retained significant surface amorphousness during storage. This form was also prepared in the pure form and further characterized. Overall, this study demonstrates the potential value of nonlinear optical imaging, together with more established solid-state analysis methods, to understand complex surface crystallization behavior and its influence on drug dissolution during the development of amorphous drugs and dosage forms.

Investigation of Ethylene Oxide-co-propylene Oxide for Dissolution Enhancement of Hot-Melt Extruded Solid Dispersions

The optimal design of amorphous solid dispersion formulations requires the use of excipients to maintain supersaturation and improve physical stability to ensure shelf-life stability and better absorption during intestinal transit, respectively. Blends of excipients (surfactants and polymers) are often used within pharmaceutical products to improve the oral delivery of Biopharmaceutical Classification System class II drugs. Therefore, in this study, a dissolution enhancer, poloxamer 407 (P407), was investigated to determine its effect on the dissolution properties and on the amorphous nature of the active pharmaceutical ingredient contained in the formulation. Phase solubility studies of indomethacin (INM) in aqueous solutions of P407 and poly(vinylpyrrolidone-vinyl acetate copolymer) showed an increase in the kinetic solubility of INM compared with the pure drug at 37°C with a K_a value of 0.041 μg/mL. The solid dispersions showed a higher dissolution rate when compared to pure and amorphous drugs when performed in pH buffer 1.2 with a kinetic solubility of 21 μg/mL. The stability data showed that the amorphous drug in solid solutions with poly(vinylpyrrolidone-vinyl acetate copolymer) and P407 remained amorphous, and the %P407 loading had no effect on the amorphous stability of INM. This study concluded that the amorphous solid dispersion contributed to the increased solubility of INM.

Impact of Eudragit EPO and hydroxypropyl methylcellulose on drug release rate, supersaturation, precipitation outcome and redissolution rate of indomethacin amorphous solid dispersions

The purpose of this work was to evaluate the impact of polymer(s) on the dissolution rate, supersaturation and precipitation of indomethacin amorphous solid dispersions (ASD), and to understand the link between precipitate characteristics and redissolution kinetics. The crystalline and amorphous solubilities of indomethacin were determined in the absence and presence of hydroxypropylmethyl cellulose (HPMC) and/or Eudragit ^® EPO to establish relevant phase boundaries. At acidic pH, HPMC could maintain supersaturation of the drug by effectively inhibiting solution crystallization while EPO increased both the crystalline and amorphous solubility of the drug, but did not inhibit crystallization. The HPMC dispersion dissolved relatively slowly without undergoing crystallization while the supersaturation generated by rapid dissolution of the EPO ASD was short-lived due to crystallization. The crystals thus generated underwent rapid redissolution upon pH increase, dissolving faster than the reference crystalline material, and at a comparable rate to the amorphous HPMC dispersion. A ternary dispersion containing both EPO and HPMC dissolved rapidly, generating an apparent drug concentration that exceeded the amorphous solubility of indomethacin, leading to the formation of a new nanosized droplet phase. These nanodroplets dissolved virtually immediately when the pH was increased. In conclusion, the concentration-time profiles achieved from indomethacin ASD dissolution are a complex interplay of drug release rate, precipitation kinetics and outcome, and precipitate redissolution rate, whereby each of these processes is highly dependent on the polymer(s) employed in the formulation.

The Need for Restructuring the Disordered Science of Amorphous Drug Formulations

The alarming numbers of poorly soluble discovery compounds have centered the efforts towards finding strategies to improve the solubility. One of the attractive approaches to enhance solubility is via amorphization despite the stability issue associated with it. Although the number of amorphous-based research reports has increased tremendously after year 2000, little is known on the current research practice in designing amorphous formulation and how it has changed after the concept of solid dispersion was first introduced decades ago. In this review we try to answer the following questions: What model compounds and excipients have been used in amorphous-based research? How were these two components selected and prepared? What methods have been used to assess the performance of amorphous formulation? What methodology have evolved and/or been standardized since amorphous-based formulation was first introduced and to what extent have we embraced on new methods? Is the extent of research mirrored in the number of marketed amorphous drug products? We have summarized the history and evolution of amorphous formulation and discuss the current status of amorphous formulation-related research practice. We also explore the potential uses of old experimental methods and how they can be used in tandem with computational tools in designing amorphous formulation more efficiently than the traditional trial-and-error approach.

Topical ophthalmic lipid nanoparticle formulations (SLN, NLC) of indomethacin for delivery to the posterior segment ocular tissues

PURPOSE

The objective of the present study was to formulate indomethacin (IN)-loaded solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) and to investigate their potential use in topical ocular delivery.

METHODS

IN SLNs (0.1% w/v) and NLCs (0.8% w/v) were prepared, characterized and evaluated. Their in vitro release and flux profiles across the cornea and sclera-choroid-RPE (trans-SCR) tissues and in vivo ocular tissue distribution were assessed. Furthermore, chitosan chloride (CS) (mol. wt.<200kDa), a cationic and water-soluble penetration enhancer, was used to modify the surface of the SLNs, and its effect was investigated through in vitro transmembrane penetration and in vivo distribution tissue studies.

RESULTS

For the IN-SLNs, IN-CS-SLNs and IN-NLCs, the particle size was 226±5, 265±8, and 227±11nm, respectively; the zeta potential was -22±0.8, 27±1.2, and -12.2±2.3mV, respectively; the polydispersity index (PDI) was 0.17, 0.30, and 0.23, respectively; and the entrapment efficiency (EE) was 81±0.9, 91.5±3.2 and 99.8±0.2%, respectively. The surface modification of the SLNs with CS increased the ocular penetration of IN. The NLCs maintained significantly higher IN concentrations in all ocular tissues tested compared to the other formulations evaluated in vivo.

CONCLUSION

The results suggest that lipid-based particulate systems can serve as viable vehicles for ocular delivery. The NLC formulations demonstrated increased drug loading capability, entrapment and delivery to anterior and posterior segment ocular tissues.