Relationship between dissolution and bioavailability for nimodipine colloidal dispersions: The critical size in improving bioavailability

Cholecalciferol complexation with hydroxypropyl-β-cyclodextrin (HPBCD) and its molecular dynamics simulation

The focus of the current study is to investigate cholecalciferol (vitamin D3) solubilization by hydroxypropyl-β-cyclodextrin (HPBCD) complexation through experimental and computational studies. Phase solubility diagram of vitamin D3 (completely insoluble in water) has an AP profile revealing a deviation from a linear regression with HPBCD concentration increase. Differential scanning calorimetry (DSC) is the best tool to confirm complex formation by disappearance of cholecalciferol exothermic peak in cholecalciferol-HPBCD complex thermogram, due to its amorphous state by entering HPBCD inner hydrophobic cavity, similarly validated by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). AP solubility diagram profile can be associated with cholecalciferol-HPBCD complex instability in liquid phase requiring spray drying to bring it to a solid dispersion state (always more stable) illustrated by scanning electron microscopy (SEM). Computational studies led to a deeper understanding and clarification, at molecular level, of the interactions within cholecalciferol-HPBCD complex. Thermodynamics and geometry of the complex were investigated by molecular dynamics (MD) simulation.

Intra-articular drug delivery systems for osteoarthritis therapy: shifting from sustained release to enhancing penetration into cartilage

Osteoarthritis (OA) is a progressive chronic inflammation that leads to cartilage degeneration. OA Patients are commonly given pharmacological treatment, but the available treatments are not sufficiently effective. The development of sustained-release drug delivery systems (DDSs) for OA may be an attractive strategy to prevent rapid drug clearance and improve the half-life of a drug at the joint cavity. Such delivery systems will improve the therapeutic effects of anti-inflammatory effects in the joint cavity. Whereas, for disease-modifying OA drugs (DMOADs) which target chondrocytes or act on mesenchymal stem cells (MSCs), the cartilage-permeable DDSs are required to maximize their efficacy. This review provides an overview of joint structure in healthy and pathological conditions, introduces the advances of the sustained-release DDSs and the permeable DDSs, and discusses the rational design of the permeable DDSs for OA treatment. We hope that the ideas generated in this review will promote the development of effective OA drugs in the future.

Facile synthesis of PEI-based crystalline templated mesoporous silica with molecular chirality for improved oral delivery of the poorly water-soluble drug

The aim of this study was to build up a novel chiral mesoporous silica called PEIs@TA-CMS through a facile biomimetic strategy and to explore its potential to serve as a drug carrier for improving the delivery efficiency of poorly water-soluble drug. PEIs@TA-CMS was synthesized by using a chiral crystalline complex associated of tartaric acid and polyethyleneimine (PEIs) as templates, scaffolds and catalysts. The structural features including morphology, size, pore structure and texture properties were systematacially studied. The results showed that PEIs@TA-CMS was monodispersed spherical nanoparticles in a uniformed diameter of 120–130 nm with well-developed pore structure (S_BET: 1009.94 m²/g, pore size <2.21 nm). Then PEIs@TA-CMS was employed as nimodipine (NMP) carrier and compared with the drug carry ability of MCM41. After drug loading, NMP was effectively transformed from the crystalline state to an amorphous state due to the space confinement in mesopores. As expected, PEIs@TA-CMS had superiority in both drug loading and drug release compared to MCM41. It could incorporate NMP with high efficiency, and the dissolution-promoting effect of PEIs@TA-CMS was more obvious because of the unique interconnected curved pore channels. Meanwhile, PEIs@TA-CMS could significantly improve the oral adsorption of NMP to a satisfactory level, which showed approximately 3.26-fold higher in bioavailability, and could effectively prolong the survival time of mice on cerebral anoxia from 10.98 to 17.33 min.

Cooperative effect of polyvinylpyrrolidone and HPMC E5 on dissolution and bioavailability of nimodipine solid dispersions and tablets

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HPMC was used to inhibit crystallization both in solid dispersions and tablets.

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Fluid-bed technique was employed to realize the scaling-up of solid dispersions.

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Dissolution results became reliable with the usage of discriminatory media.

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The results of the bioavailability showed a higher AUC_{0–12 h} value for fluid-bed tablets, compared to Nimotop™.

Solid dispersion (SD) systems have been extensively used to increase the dissolution and bioavailability of poorly water-soluble drugs. To circumvent the limitations of polyvinylpyrrolidone (PVP) dispersions, HPMC E5 was applied in the formulation process and scaling-up techniques, simultaneously. In this study, SD of nimodipine (NMP) and corresponding tablets were prepared through solvent method and fluid bed granulating one step technique, respectively. Discriminatory dissolution media were used to obtain reliable dissolution results. Meanwhile, the stability study of SDs was investigated with storage under high temperature and humidity conditions. Moreover, the solubility of SDs was measured to explore the effect of carriers. The preparations were characterized by DSC, PXRD, and FTIR. Dramatical improvements in the dissolution rate of NMP were achieved by the ingenious combination of the two polymers. Binary NMP/PVP/HPMC-SDs released steadily, while the dissolution of single NMP/PVP-SDs decreased rapidly in water. The fluid-bed tablets (FB-T) possessed a similar dissolution behavior to the commercial Nimotop™ tablets. The characterization patterns implied that NMP existed in an amorphous state in our SDs. Furthermore, the results of stability tests suggested a better stability of the binary SDs. A special cooperative effect of PVP and HPMC was discovered on dissolution characteristics of NMP SDs and tablets, which could be extended to other drugs henceforth. Finally, the bioavailability of FB-T was evaluated in beagle dogs with Nimotop™ as the reference, and the results showed a higher AUC_0–12hvalue for FB-T.

The role of particle size of glyburide crystals in improving its oral absorption

Currently, nanosizing is becoming increasingly prevalent as an efficient way for the improvement of oral drug absorption. This study mainly focuses on two points, namely the crystal properties, and the in vitro and in vivo characterizations of drug crystals during the nanosizing process. We used glyburide, an oral type 2 diabetes (T2D) medication, as our model drug. We sought to reduce the crystalline size of this drug and evaluate its absorption properties by comparing it with the original coarse drug because of previous reports about its gastrointestinal absorption insufficiency. Glyburide crystals, ranging from 237.6 to 4473 nm were prepared successfully by jet milling and media milling. The particle sizes and the crystal morphology were analyzed by characterization of the solid states, equilibrium solubility, and dissolution behavior. Additionally, pharmacokinetic study was performed in SD rats. The solid state results indicated a loss in crystallinity, amide-imidic acid interconversion, and partial amorphization during nanosizing. Further, in in vitro tests, nanocrystal formulations remarkably increased the solubility and dissolution of the drug (compared to microcrystals). In the in vivo test, reducing the particle size from 601.3 to 312.5 nm showed no improvement on the C _max and AUC _(0-36 h) values, while a profound slowing of the drug elimination occurred with reduction of particle size. Further reduction from 312.5 to 237.6 nm lead to a significant increase (p < 0.001) of the AUC _(0-36 h) from 6857.8 ± 369.3 ng mL^-1 h to 12,928.3 ± 1591.4 ng mL^-1 h, respectively, in rats. Our present study confirmed that nanosizing has a tremendous impact on promoting the oral absorption of glyburide.

One-step self-assembled nanomicelles for improving the oral bioavailability of nimodipine

Our study aimed to develop a self-assembled nanomicelle for oral administration of nimodipine (NIM) with poor water solubility. Using Solutol(®) HS15, the NIM-loaded self-assembled nanomicelles displayed a near-spherical morphology with a narrow size distribution of 12.57 ± 0.21 nm (polydispersity index =0.071 ± 0.011). Compared with Nimotop(®) (NIM tablets), the intestinal absorption of NIM from NIM nanomicelle in rats was improved by 3.13- and 2.25-fold in duodenum and jejunum at 1 hour after oral administration. The cellular transport of NIM nanomicelle in Caco-2 cell monolayers was significantly enhanced compared to that of Nimotop(®). Regarding the transport pathways, clathrin, lipid raft/caveolae, and macropinocytosis mediated the cell uptake of NIM nanomicelles, while P-glycoprotein and endoplasmic reticulum/Golgi complex (ER/Golgi) pathways were involved in exocytosis. Pharmacokinetic studies in our research laboratory have showed that the area under the plasma concentration-time curve (AUC0-∞) of NIM nanomicelles was 3.72-fold that of Nimotop(®) via oral administration in rats. Moreover, the NIM concentration in the brain from NIM nanomicelles was dramatically improved. Therefore, Solutol(®) HS15-based self-assembled nanomicelles represent a promising delivery system to enhance the oral bioavailability of NIM.

Experimental and computational studies of physicochemical properties influence NSAID-cyclodextrin complexation

The objective of this research was to investigate physicochemical properties of an active pharmaceutical ingredient (API) that influence cyclodextrin complexation through experimental and computational studies. Native β-cyclodextrin (B-CD) and two hydroxypropyl derivatives were first evaluated by conventional phase solubility experiments for their ability to complex four poorly water-soluble nonsteroidal anti-inflammatory drugs (NSAIDs). Differential scanning calorimetry was used to confirm complexation. Secondly, molecular modeling was used to estimate Log P and aqueous solubility (S o) of the NSAIDs. Molecular dynamics simulations (MDS) were used to investigate the thermodynamics and geometry of drug-CD cavity docking. NSAID solubility increased linearly with increasing CD concentration for the two CD derivatives (displaying an AL profile), whereas increases in drug solubility were low and plateaued in the B-CD solutions (type B profile). The calculated Log P and S o of the NSAIDs were in good concordance with experimental values reported in the literature. Side chain substitutions on the B-CD moiety did not significantly influence complexation. Explicitly, complexation and the associated solubility increase were mainly dependent on the chemical structure of the NSAID. MDS indicated that each NSAID-CD complex had a distinct geometry. Moreover, complexing energy had a large, stabilizing, and fairly constant hydrophobic component for a given CD across the NSAIDs, while electrostatic and solvation interaction complex energies were quite variable but smaller in magnitude.

Bexarotene nanocrystal-Oral and parenteral formulation development, characterization and pharmacokinetic evaluation

Bexarotene (Targretin®) is a synthetic retinoid that selectively activates the retinoid X receptor subfamily of retinoid receptors and exhibits potent anti-tumor activity. However, the poor solubility and bioavailability limit its application. The main aim of this study is to investigate the potential of oral and parenteral nanocrystals in enhancing the bioavailability of bexarotene. In this work, the orthogonal design was used to screen the optimum stabilizers and precipitation-combined microfluidization method was employed to obtain the optimal nanocrystals. According to DSC, X-ray diffraction analysis and Raman examination, the nanocrystals were still in crystalline state after the preparation procedure. By reducing the particle size, the in vitro dissolution rate of bexarotene was increased significantly. The in vivo test was carried out in rats and pharmacokinetic parameters of the bexarotene solution and bexarotene nanocrystals were compared after gavage and intravenous administration. The higher AUC and lower Cmax indicated that oral bexarotene nanocrystals significantly increased the bioavailability of bexarotene and decreased its side effects. Compared to the oral nanocrystals, the intravenous nanocrystals cut losses and increased bioavailability because of the absence of first pass effect and enterohepatic circulation.

Profiling biopharmaceutical deciding properties of absorption of lansoprazole enteric-coated tablets using gastrointestinal simulation technology

The aim of the present study was to correlate in vitro properties of drug formulation to its in vivo performance, and to elucidate the deciding properties of oral absorption. Gastrointestinal simulation technology (GST) was used to simulate the in vivo plasma concentration-time curve and was implemented by GastroPlus™ software. Lansoprazole, a typical BCS class II drug, was chosen as a model drug. Firstly, physicochemical and pharmacokinetic parameters of lansoprazole were determined or collected from literature to construct the model. Validation of the developed model was performed by comparison of the predicted and the experimental plasma concentration data. We found that the predicted curve was in a good agreement with the experimental data. Then, parameter sensitivity analysis (PSA) was performed to find the key parameters of oral absorption. The absorption was particularly sensitive to dose, solubility and particle size for lansoprazole enteric-coated tablets. With a single dose of 30 mg and the solubility of 0.04 mg/ml, the absorption was complete. A good absorption could be achieved with lansoprazole particle radius down to about 25 μm. In summary, GST is a useful tool for profiling biopharmaceutical deciding properties of absorption of lansoprazole enteric-coated tablets and guiding the formulation optimization.

Nimodipine nanocrystals for oral bioavailability improvement: preparation, characterization and pharmacokinetic studies

This study intended to develop nimodipine (NMD) nanocrystals with different sizes for oral administration and to investigate the relationship between dissolution and pharmacokinetics for NMD nanocrystals and Nimotop(®). NMD nanocrystals were prepared by combination of microprecipitation and high pressure homogenization and were further lyophilized. The particle size, morphology and aqueous solubility of the NMD nanocrystals were determined. With Nimotop(®) as the control, the dissolution rate was evaluated and the pharmacokinetic study was undertaken in beagle dogs. NMD nanocrystals with mean diameters of about 159.0, 503.0 and 833.3 nm were prepared, respectively. The lyophilization didn't affect the particle sizes of the redispersed nanocrystals. The aqueous solubility was significantly improved and displayed a size-dependent manner. The nanocrystals exhibited lower dissolution patterns than Nimotop(®) under non-sink condition, but bioavailability of the two nanocrystals (159.0 and 833.3 nm) was equivalent, about 2.6-fold higher than Nimotop(®). In conclusion, oral nanocrystal drug delivery system was a promising strategy in improving the oral bioavailability of poorly soluble or insoluble drugs. But we could not establish a favorable in vitro in vivo correlation for NMD nanocrystals and Nimotop(®) and thus the oral absorption mechanism of the NMD nanocrystals required further study.

Nimodipine nanocrystals for oral bioavailability improvement: role of mesenteric lymph transport in the oral absorption

PURPOSE

We had conducted a comprehensive study on preparation, characterization and pharmacokinetics of nimodipine nanocrystals for oral administration previously, and nimodipine nanocrystals displayed lower dissolution profiles but higher bioavailability than Nimotop(®). In this study, we aimed at elucidating the reasons of unfavorable in vitro in vivo correlation for NMD nanocrystals and Nimotop(®) with a hypothesis that special oral absorption mechanism was involved in the absorption of nimodipine nanocrystals.

METHODS

Investigations of oral absorption mechanism of the nanocrystals were performed on everted gut sac models, lymphatically (mesenteric lymph duct) cannulated SD rats, Caco-2 cell monolayers and chylomicron flow blocking rats, respectively.

RESULTS

The permeability of nanocrystals in duodenum, ileum and colon was not superior to that of Nimotop(®), suggestive of special absorption mechanisms involved. Exudates of nanocrystals from enterocytes were detected in mesenteric lymphatic fluids using a transmission electron microscope, and the bioavailability was only about half of the control after the mesenteric lymph was blocked. The nanocrystals were taken up by enterocytes via macropinocytosis and caveolin-mediated endocytosis pathways.

CONCLUSIONS

It was impossible to establish a favorable in vitro in vivo correlation for NMD nanocrystals and Nimotop(®), because portions of the nanocrystals underwent macropinocytosis and caveolin-mediated endocytosis by enterocytes as intact nanocrystal forms, then bypassed the liver first-pass metabolism.