Elucidating the effect of crystallization on drug release from amorphous solid dispersions in soluble and insoluble carriers

Changes in drug crystallinity in a commercial tacrolimus amorphous formulation result in variable pharmacokinetics

Tacrolimus capsules contain the drug as the amorphous form. It is well known that drug crystallinity is a risk factor for the performance of amorphous formulations. This study investigated the impact of varying levels of crystalline drug on the pharmacokinetics of tacrolimus following oral dosing of a 5 mg capsule under fasting conditions. Two treatments with percent crystallinity of 20% and 50% were achieved by exposing a marketed generic tacrolimus product to open dish storage conditions of 35 °C and 75% relative humidity (RH) for up to 20 days. Crystallinity was monitored with X-ray powder diffraction. Prograf®, the reference listed drug (RLD), an amorphous generic drug product, and generic drug products containing 20% and 50% crystalline tacrolimus were evaluated. All four treatments were administered to healthy participants in a randomized, single-dose, four-treatment, four-period, four-way crossover study. Blood sampling occurred over 24 h. The amorphous generic tacrolimus product was determined not to be bioequivalent to the RLD. The capsules containing both 20% and 50% crystalline tacrolimus also failed the bioequivalence recommendations when compared to the amorphous generic or to the RLD. Both levels of crystalline tacrolimus resulted in BE failure for both Cmax and AUC parameters. The impact of tacrolimus crystallization was greater for maximum blood concentration (Cmax) values relative to the area-under-the-curve (AUC) values. This study demonstrates that crystalline tacrolimus formed in a marketed generic product and these changes resulted in variable pharmacokinetics which could be of significant clinical concern.

Antitumoral melatonin-loaded nanostructured lipid carriers

Aim: Cancer constitutes the second leading cause of death worldwide, with conventional therapies limited by significant side effects. Melatonin (MEL), a natural compound with antitumoral properties, suffers from instability and low solubility. To overcome these issues, MEL was encapsulated into nanostructured lipid carriers (MEL-NLC) containing rosehip oil to enhance stability and boost its antitumoral activity.Methods: MEL-NLC were optimized by a design of experiments approach and characterized for their physicochemical properties. Stability and biopharmaceutical behavior were assessed, along with interaction studies and in vitro antitumoral efficacy against various cancer cell lines.Results: Optimized MEL-NLC exhibited desirable physicochemical characteristics, including small particle size and sustained MEL release, along with long-term stability. In vitro studies demonstrated that MEL-NLC selectively induced cytotoxicity in several cancer cell lines while sparing healthy cells.Conclusion: MEL-NLC represent a promising alternative for cancer, combining enhanced stability and targeted antitumoral activity, potentially overcoming the limitations of conventional treatments.

Novel nanostructured lipid carriers loading Apigenin for anterior segment ocular pathologies

Dry eye disease (DED) is a chronic multifactorial disorder of the ocular surface caused by tear film dysfunction and constitutes one of the most common ocular conditions worldwide. However, its treatment remains unsatisfactory. While artificial tears are commonly used to moisturize the ocular surface, they do not address the underlying causes of DED. Apigenin (APG) is a natural product with anti-inflammatory properties, but its low solubility and bioavailability limit its efficacy. Therefore, a novel formulation of APG loaded into biodegradable and biocompatible nanoparticles (APG-NLC) was developed to overcome the restricted APG stability, improve its therapeutic efficacy, and prolong its retention time on the ocular surface by extending its release. APG-NLC optimization, characterization, biopharmaceutical properties and therapeutic efficacy were evaluated. The optimized APG-NLC exhibited an average particle size below 200 nm, a positive surface charge, and an encapsulation efficiency over 99 %. APG-NLC exhibited sustained release of APG, and stability studies demonstrated that the formulation retained its integrity for over 25 months. In vitro and in vivo ocular tolerance studies indicated that APG-NLC did not cause any irritation, rendering them suitable for ocular topical administration. Furthermore, APG-NLC showed non-toxicity in an epithelial corneal cell line and exhibited fast cell internalization. Therapeutic benefits were demonstrated using an in vivo model of DED, where APG-NLC effectively reversed DED by reducing ocular surface cellular damage and increasing tear volume. Anti-inflammatory assays in vivo also showcased its potential to treat and prevent ocular inflammation, particularly relevant in DED patients. Hence, APG-NLC represent a promising system for the treatment and prevention of DED and its associated inflammation.

Dually Active Apigenin-Loaded Nanostructured Lipid Carriers for Cancer Treatment

Purpose

Cancer is one of the major causes of death worldwide affecting more than 19 million people. Traditional cancer therapies have many adverse effects and often result in unsatisfactory outcomes. Natural flavones, such as apigenin (APG), have demonstrated excellent antitumoral properties. However, they have a low aqueous solubility. To overcome this drawback, APG can be encapsulated in nanostructured lipid carriers (NLC). Therefore, we developed dual NLC encapsulating APG (APG-NLC) with a lipid matrix containing rosehip oil, which is known for its anti-inflammatory and antioxidant properties.

Methods

Optimisation, physicochemical characterisation, biopharmaceutical behaviour, and therapeutic efficacy of this novel nanostructured system were assessed.

Results

APG-NLC were optimized obtaining an average particle size below 200 nm, a surface charge of -20 mV, and an encapsulation efficiency over 99%. The APG-NLC released APG in a sustained manner, and the results showed that the formulation was stable for more than 10 months. In vitro studies showed that APG-NLC possess significant antiangiogenic activity in ovo and selective antiproliferative activity in several cancer cell lines without exhibiting toxicity in healthy cells.

Conclusion

APG-NLC containing rosehip oil were optimised. They exhibit suitable physicochemical parameters, storage stability for more than 10 months, and prolonged APG release. Moreover, APG-NLC were internalised inside tumour cells, showing the capacity to cause cytotoxicity in cancer cells without damaging healthy cells.

Crystallinity: A Complex Critical Quality Attribute of Amorphous Solid Dispersions

Does the performance of an amorphous solid dispersion rely on having 100% amorphous content? What specifications are appropriate for crystalline content within an amorphous solid dispersion (ASD) drug product? In this Perspective, the origin and significance of crystallinity within amorphous solid dispersions will be considered. Crystallinity can be found within an ASD from one of two pathways: (1) incomplete amorphization, or (2) crystal creation (nucleation and crystal growth). While nucleation and crystal growth is the more commonly considered pathway, where crystals originate as a physical stability failure upon accelerated or prolonged storage, manufacturing-based origins of crystallinity are possible as well. Detecting trace levels of crystallinity is a significant analytical challenge, and orthogonal methods should be employed to develop a holistic assessment of sample properties. Probing the impact of crystallinity on release performance which may translate to meaningful clinical significance is inherently challenging, requiring optimization of dissolution test variables to address the complexity of ASD formulations, in terms of drug physicochemical properties (e.g., crystallization tendency), level of crystallinity, crystal reference material selection, and formulation characteristics. The complexity of risk presented by crystallinity to product performance will be illuminated through several case studies, highlighting that a one-size-fits-all approach cannot be used to set specification limits, as the risk of crystallinity can vary widely based on a multitude of factors. Risk assessment considerations surrounding drug physicochemical properties, formulation fundamentals, physical stability, dissolution, and crystal micromeritic properties will be discussed.

Effects of Additives on the Physical Stability and Dissolution of Polymeric Amorphous Solid Dispersions: a Review

Polymeric amorphous solid dispersion (ASD) is a popular approach for enhancing the solubility of poorly water-soluble drugs. However, achieving both physical stability and dissolution performance in an ASD prepared with a single polymer can be challenging. Therefore, a secondary excipient can be added. In this paper, we review three classes of additives that can be added internally to ASDs: (i) a second polymer, to form a ternary drug-polymer-polymer ASD, (ii) counterions, to facilitate in situ salt formation, and (iii) surfactants. In an ASD prepared with a combination of polymers, each polymer exerts a unique function, such as a stabilizer in the solid state and a crystallization inhibitor during dissolution. In situ salt formation in ASD usually leads to substantial increases in the glass transition temperature, contributing to improved physical stability. Surfactants can enhance the wettability of ASD particles, thereby promoting rapid drug release. However, their potential adverse effects on physical stability and dissolution, resulting from enhanced molecular mobility and competitive molecular interaction with the polymer, respectively, warrant careful consideration. Finally, we discuss the impact of magnesium stearate and inorganic salts, excipients added externally upon downstream processing, on the solid-state stability as well as the dissolution of ASD tablets.

Amorphous solid dispersions in high-swelling, low-substituted hydroxypropyl cellulose for enhancing the delivery of poorly soluble drugs

Amorphous solid dispersions (ASDs) based on water-insoluble hydrophilic polymers can sustain supersaturation in their kinetic solubility profiles (KSPs) compared to soluble carriers. However, in the limit of very high swelling capacity, the achievable extent of drug supersaturation has not been fully examined. This study explores the limiting supersaturation behavior of ASDs of poorly soluble indomethacin (IND) and posaconazole (PCZ) based on a high-swelling excipient, low-substituted hydroxypropyl cellulose (L-HPC). Using IND as a reference, we showed that the rapid initial supersaturation buildup in the KSP of IND ASD can be simulated through sequential IND infusion steps, however at large times the KSP of IND release from ASD appears more sustained than direct IND infusion. This has been attributed to potential trapping of seed crystals generated in the L-HPC gel matrix thus limiting their growth and rate of desupersaturation. Similar result is also expected in PCZ ASD. Furthermore, the current drug loading process for ASD preparation resulted in the agglomeration of L-HPC based ASD particles, producing granules of up to 300-500µm (cf. 20µm individual particle), with distinct kinetic solubility profiles. This feature makes L-HPC particularly suitable as ASD carriers for fine tuning of supersaturation to achieve enhanced bioavailability for poorly soluble drugs.

Impact of Crystal Nuclei on Dissolution of Amorphous Drugs

Amorphous drugs are used to improve bioavailability of poorly water-soluble drugs. Crystallization must be managed to take full advantage of this formulation strategy. Crystallization of amorphous drugs proceeds in a sequence of crystal nucleation and growth, with different kinetics. At low temperatures, crystal nucleation is fast, but crystal growth is slow. Therefore, amorphous drugs may generate dense but nanoscale crystal nuclei. Such tiny nuclei cannot be detected using routine powder X-ray diffraction (PXRD) and polarized light microscopy (PLM). However, they may negate the dissolution advantage of amorphous drugs. In this work, for the first time, the impact of crystal nuclei on dissolution of amorphous drugs was studied by monitoring the real-time dissolution from amorphous drug films, with and without crystal nuclei, and the evolving crystallinity in the films. Three model drugs (ritonavir/RTV, posaconazole/POS, and nifedipine/NIF) were chosen to represent different crystallization tendencies in the supercooled liquid state, namely, slow-nucleation-and-slow-growth (SN-SG), fast-nucleation-and-slow-growth (FN-SG), and fast-nucleation-and-fast-growth (FN-FG), respectively. We find that although the amorphous films containing nuclei do not show obvious differences from the nuclei-free films under PLM and PXRD before dissolution, they have inferior dissolution performance relative to the nuclei-free amorphous films. For SN-SG drug RTV, crystal nuclei have negligible impact on the crystallization of amorphous films, dissolution rate, and supersaturation achieved. However, they cause earlier de-supersaturation by inducing crystallization in solution as heterogeneous seeds. For FN-SG drug POS and FN-FG drug NIF, crystal nuclei accelerate crystallization in the amorphous films leading to lower supersaturation achieved with POS, and elimination of any supersaturation with NIF. Dissolution profiles of amorphous films can be further analyzed using a derivative function of the apparent dissolution rate, which yields amorphous solubility, initial intrinsic dissolution rate, and onset of crystallization in the amorphous films. This study highlights that although crystal nuclei are undetectable with routine analytical methods, they can significantly negate, or even eliminate, the dissolution advantage of amorphous drugs. Hence, understanding crystal nucleation process and developing approaches to prevent it are necessary to fully realize the benefits of amorphous solids.

Effect of PEGylation on drug uptake, biodistribution, and tissue toxicity of efavirenz-ritonavir loaded PAMAM G4 dendrimers

The present investigations aimed to compare the efficiency of PAMAM G4 (PG4) and PEGylated PAMAM G4 (PPG4) dendrimers as novel nanocarriers for the treatment of HIV-1. Synthesized PG4 and PPG4 dendrimers were confirmed by electrospray ionization and particle size with its morphology. The anti-human immunodeficiency virus (HIV) drug efavirenz (EFV) with a booster dose of ritonavir (RTV) was encapsulated into PG4 and PPG4 formerly noted as PG4ER and PPG4ER, respectively. Further, evaluated for dendrimers mediated solubilization, drug release, cytotoxicity, drug uptake, plasma, and tissue pharmacokinetics, and histopathology. PG4ER and PPG4ER both promoted a prolonged release of EFV in weakly acidic pH 4 up to 84 h and 132 h, respectively. The results of the cytotoxicity assay and drug uptake study showed that PPG4ER was safe and biocompatible up to 12.5 µg/ml. The plasma pharmacokinetic profile of EFV and RTV was significantly increased by PPG4ER with prolonged t_1/2 up to three times as compared to free EFV-RTV and PG4ER. Histopathological analysis showed remarkably lower tissue toxicity in PPG4ER as compared to free EFV-RTV. Therefore, overall data suggested that PPG4 has a great potential for prolonged release of EFV and RTV with enhanced bioavailability and lower toxicity.

Continuous Manufacturing and Molecular Modeling of Pharmaceutical Amorphous Solid Dispersions

Amorphous solid dispersions enhance solubility and oral bioavailability of poorly water-soluble drugs. The escalating number of drugs with poor aqueous solubility, poor dissolution, and poor oral bioavailability is an unresolved problem that requires adequate interventions. This review article highlights recent solubility and bioavailability enhancement advances using amorphous solid dispersions (ASDs). The review also highlights the mechanism of enhanced dissolution and the challenges faced by ASD-based products, such as stability and scale-up. The role of process analytical technology (PAT) supporting continuous manufacturing is highlighted. Accurately predicting interactions between the drug and polymeric carrier requires long experimental screening methods, and this is a space where computational tools hold significant potential. Recent advancements in data science, computational tools, and easy access to high-end computation power are set to accelerate ASD-based research. Hence, particular emphasis has been given to molecular modeling techniques that can address some of the unsolved questions related to ASDs. With the advancement in PAT tools and artificial intelligence, there is an increasing interest in the continuous manufacturing of pharmaceuticals. ASDs are a suitable option for continuous manufacturing, as production of a drug product from an ASD by direct compression is a reality, where the addition of multiple excipients is easy to avoid. Significant attention is necessary for ongoing clinical studies based on ASDs, which is paving the way for the approval of many new ASDs and their introduction into the market.

Water-Resistant Drug-Polymer Interaction Contributes to the Formation of Nano-Species during the Dissolution of Felodipine Amorphous Solid Dispersions

Drug-polymer interactions are of great importance in amorphous solid dispersion (ASD) formulation for both dissolution performance and physical stability considerations. In this work, three felodipine ASD systems with drug loading ranging from 5 to 20% were prepared using PVP, PVP-VA, or HPMC-AS as the polymer matrix. The amorphization and homogeneity were confirmed by differential scanning calorimetry and powder X-ray diffraction. The intrinsic dissolution behavior of these ASDs was studied in 0.05 M HCl and phosphate-buffered saline (PBS) (pH 6.5). In 0.05 M HCl, PVP-VA ASDs with low drug loading (<15%) showed rapid dissolution accompanied with nano-species generation, while in the PVP system, rapid dissolution and nano-species generation were observed only when drug loading was less than 10%, and HPMC-AS ASDs always released slowly with no nano-species formation. In PBS, PVP-VA ASDs with drug loading less than 10% showed rapid dissolution accompanied with nano-species generation, while for PVP ASDs, rapid dissolution and nano-species generation were observed only when drug loading was 5%. However, 20% drug loading HPMC-AS ASDs exhibited rapid dissolution of felodipine and nano-species generation. When the drug loading was above the transition point of PVP-VA ASDs and PVP ASDs, the release rate was significantly lowered, and no nano-species was generated. To understand this phenomenon, drug-polymer interactions were studied using the melting point depression method and the Flory-Huggins model fitting. The Flory-Huggins interaction parameters (χ) for felodipine/HPMC-AS, felodipine/PVP, and felodipine/PVP-VA were determined to be 0.62 ± 0.07, -0.55 ± 0.20, and -1.02 ± 0.21, respectively, indicating the existence of the strongest attractive molecular interaction between felodipine and PVP-VA, followed by felodipine/PVP, but not in felodipine/HPMC-AS. Furthermore, dynamic vapor sorption further revealed that the molecular interactions between felodipine and PVP or PVP-VA were resistant to water. We concluded that water-resistant drug-polymer interactions in felodipine/polymer systems were responsible for the formation of nano-species, which further facilitated the rapid initial drug dissolution.

Formulating a heat- and shear-labile drug in an amorphous solid dispersion: Balancing drug degradation and crystallinity

We seek to further addresss the questions posed by Moseson et al. regarding whether any residual crystal level, size, or characteristic is acceptable in an amorphous solid dispersion (ASD) such that its stability, enhanced dissolution, and increased bioavailability are not compromised. To address this highly relevant question, we study an interesting heat- and shear-labile drug in development, LY3009120. To study the effects of residual crystallinity and degradation in ASDs, we prepared three compositionally identical formulations (57–1, 59–4, and 59–5) using the KinetiSol process under various processing conditions to obtain samples with various levels of crystallinity (2.3%, 0.9%, and 0.1%, respectively) and degradation products (0.74%, 1.97%, and 3.12%, respectively). Samples with less than 1% crystallinity were placed on stability, and we observed no measurable change in the drug's crystallinity, dissolution profile or purity in the 59–4 and 59–5 formulations over four months of storage under closed conditions at 25 °C and 60% humidity. For formulations 57–1, 59–4, and 59–5, bioavailability studies in rats reveal a 44-fold, 55-fold, and 62-fold increase in mean AUC, respectively, compared to the physical mixture. This suggests that the presence of some residual crystals after processing can be acceptable and will not change the properties of the ASD over time.

Amorphous Solid Dispersions Containing Residual Crystallinity: Competition Between Dissolution and Matrix Crystallization

Crystallinity in an amorphous solid dispersion (ASD) may negatively impact dissolution performance by causing lost solubility advantage and/or seeding crystal growth leading to desupersaturation. The goal of the study was to evaluate underlying dissolution and crystallization mechanisms resulting from residual crystallinity contained within bicalutamide (BCL)/polyvinylpyrrolidone vinyl acetate copolymer (PVPVA) ASDs produced by hot melt extrusion (HME). In-line Raman spectroscopy, polarized light microscopy, and scanning electron microscopy were used to characterize crystallization kinetics and mechanisms. The fully amorphous ASD (0% crystallinity) did not dissolve completely, and underwent crystallization to the metastable polymorph (form 2), initiating in the amorphous matrix at the interface of the amorphous solid with water. Under non-sink conditions, higher extents of supersaturation were achieved because dissolution initially proceeded unhindered prior to nucleation. ASDs containing residual crystallinity had markedly reduced supersaturation. Solid-mediated crystallization (matrix crystallization) consumed the amorphous solid, growing the stable polymorph (form 1). Under sink conditions, both the fully amorphous ASD and crystalline physical mixture achieve faster release than the ASDs containing residual crystallinity. In the latter systems, matrix crystallization leads to highly agglomerated crystals with high relative surface area. Solution-mediated crystallization was not a significant driver of concentration loss, due to slow crystal growth from solution in the presence of PVPVA. The high risk stemming from residual crystallinity in BCL/PVPVA ASDs stems from (1) fast matrix crystallization propagating from crystal seeds, and (2) growth of the stable crystal form. This study has implications for dissolution performance outcomes of ASDs containing residual crystallinity.