Showing papers in "Pharmaceutical Research in 2006"

Micellar nanocarriers: pharmaceutical perspectives.

Abstract: Micelles, self-assembling nanosized colloidal particles with a hydrophobic core and hydrophilic shell are currently successfully used as pharmaceutical carriers for water-insoluble drugs and demonstrate a series of attractive properties as drug carriers. Among the micelle-forming compounds, amphiphilic copolymers, i.e., polymers consisting of hydrophobic block and hydrophilic block, are gaining an increasing attention. Polymeric micelles possess high stability both in vitro and in vivo and good biocompatibility, and can solubilize a broad variety of poorly soluble pharmaceuticals many of these drug-loaded micelles are currently at different stages of preclinical and clinical trials. Among polymeric micelles, a special group is formed by lipid-core micelles, i.e., micelles formed by conjugates of soluble copolymers with lipids (such as polyethylene glycol-phosphatidyl ethanolamine conjugate, PEG-PE). Polymeric micelles, including lipid-core micelles, carrying various reporter (contrast) groups may become the imaging agents of choice in different imaging modalities. All these micelles can also be used as targeted drug delivery systems. The targeting can be achieved via the enhanced permeability and retention (EPR) effect (into the areas with the compromised vasculature), by making micelles of stimuli-responsive amphiphilic block-copolymers, or by attaching specific targeting ligand molecules to the micelle surface. Immunomicelles prepared by coupling monoclonal antibody molecules to p-nitrophenylcarbonyl groups on the water-exposed termini of the micelle corona-forming blocks demonstrate high binding specificity and targetability. This review will discuss some recent trends in using micelles as pharmaceutical carriers.

A Review of Poloxamer 407 Pharmaceutical and Pharmacological Characteristics

Abstract: Poloxamer 407 copolymer (ethylene oxide and propylene oxide blocks) shows thermoreversible properties, which is of the utmost interest in optimising drug formulation (fluid state at room temperature facilitating administration and gel state above sol-gel transition temperature at body temperature promoting prolonged release of pharmacological agents). Pharmaceutical evaluation consists in determining the rheological behaviour (flow curve or oscillatory studies), sol-gel transition temperature, in vitro drug release using either synthetic or physiological membrane and (bio)adhesion characteristics. Poloxamer 407 formulations led to enhanced solubilisation of poorly water-soluble drugs and prolonged release profile for many galenic applications (e.g., oral, rectal, topical, ophthalmic, nasal and injectable preparations) but did not clearly show any relevant advantages when used alone. Combination with other excipients like Poloxamer 188 or mucoadhesive polymers promotes Poloxamer 407 action by optimising sol-gel transition temperature or increasing bioadhesive properties. Inclusion of liposomes or micro(nano)particles in Poloxamer 407 formulations offers interesting prospects, as well. Besides these promising data, Poloxamer 407 has been held responsible for lipidic profile alteration and possible renal toxicity, which compromises its development for parenteral applications. In addition, new findings have demonstrated immuno-modulation and cytotoxicity-promoting properties of Poloxamer 407 revealing significant pharmacological interest and, hence, human trials are in progress to specify these potential applications.

Nanotechnology: intelligent design to treat complex disease.

Abstract: The purpose of this expert review is to discuss the impact of nanotechnology in the treatment of the major health threats including cancer, infections, metabolic diseases, autoimmune diseases, and inflammations. Indeed, during the past 30 years, the explosive growth of nanotechnology has burst into challenging innovations in pharmacology, the main input being the ability to perform temporal and spatial site-specific delivery. This has led to some marketed compounds through the last decade. Although the introduction of nanotechnology obviously permitted to step over numerous milestones toward the development of the "magic bullet" proposed a century ago by the immunologist Paul Ehrlich, there are, however, unresolved delivery problems to be still addressed. These scientific and technological locks are discussed along this review together with an analysis of the current situation concerning the industrial development.

Fit-for-purpose method development and validation for successful biomarker measurement.

Abstract: Despite major advances in modern drug discovery and development, the number of new drug approvals has not kept pace with the increased cost of their development. Increasingly, innovative uses of biomarkers are employed in an attempt to speed new drugs to market. Still, widespread adoption of biomarkers is impeded by limited experience interpreting biomarker data and an unclear regulatory climate. Key differences preclude the direct application of existing validation paradigms for drug analysis to biomarker research. Following the AAPS 2003 Biomarker Workshop (J. W. Lee, R. S. Weiner, J. M. Sailstad, et al. Method validation and measurement of biomarkers in nonclinical and clinical samples in drug development. A conference report. Pharm Res22:499–511, 2005), these and other critical issues were addressed. A practical, iterative, “fit-for-purpose” approach to biomarker method development and validation is proposed, keeping in mind the intended use of the data and the attendant regulatory requirements associated with that use. Sample analysis within this context of fit-for-purpose method development and validation are well suited for successful biomarker implementation, allowing increased use of biomarkers in drug development.

Use of a glutaric acid cocrystal to improve oral bioavailability of a low solubility API.

Abstract: The bioavailability of a development candidate active pharmaceutical ingredient (API) was very low after oral dosing in dogs. In order to improve bioavailability, we sought to increase the dissolution rate of the solid form of the API. When traditional methods of forming salts and amorphous material failed to produce a viable solid form for continued development, we turned to the non-traditional approach of cocrystallization. A crystal engineering approach was used to design and execute a cocrystal screen of the API. Hydrogen bonding between the API and pharmaceutically acceptable carboxylic acids was identified as a viable synthon for associating multiple components in the solid state. A number of carboxylic acid guest molecules were tested for cocrystal formation with the API. A cocrystal containing the API and glutaric acid in a 1:1 molecular ratio was identified and the single crystal structure is reported. Physical characterization of the cocrystal showed that it is unique regarding thermal, spectroscopic, X-ray, and dissolution properties. The cocrystal solid is nonhygroscopic, and chemically and physically stable to thermal stress. Use of the cocrystal increased the aqueous dissolution rate by 18 times as compared to the homomeric crystalline form of the drug. Single dose dog exposure studies confirmed that the cocrystal increased plasma AUC values by three times at two different dose levels. APIs that are non-ionizable or demonstrate poor salt forming ability traditionally present few opportunities for creating crystalline solid forms with desired physical properties. Cocrystals are an additional class of crystalline solid that can provide options for improved properties. In this case, a crystalline molecular complex of glutaric acid and an API was identified and used to demonstrate an improvement in the oral bioavailability of the API in dogs.

Characterization of the human upper gastrointestinal contents under conditions simulating bioavailability/bioequivalence studies.

Abstract: This study was conducted to compare the luminal composition of the upper gastrointestinal tract in the fasted and fed states in humans, with a view toward designing in vitro studies to explain/predict food effects on dosage form performance. Twenty healthy human subjects received 250 mL water or 500 mL Ensure plus® (a complete nutrient drink) through a nasogastric tube and samples were aspirated from the gastric antrum or duodenum for a period up to 3.5 h, depending on location/fluid combination. Samples were analyzed for polyethylene glycol, pH, buffer capacity, osmolality, surface tension, pepsin, total carbohydrates, total protein content, and bile salts. Following Ensure plus® administration, gastric pH was elevated, buffer capacity ranged from 14 to 28 mmoL L−1 ΔpH−1 (vs. 7–18 mmol L−1 ΔpH−1), contents were hyperosmolar, gastric pepsin levels doubled, and surface tension was 30% lower than after administration of water. Post- and preprandial duodenal pH values were initially similar, but slowly decreased to 5.2 postprandially, whereas buffer capacity increased from 5.6 mmol L−1 ΔpH−1 (fasted) to 18–30 mmol L−1 ΔpH−1 (p 30%, bile salt levels were two to four times higher, luminal contents were hyperosmotic, and the presence of peptides and sugars was confirmed. This work shows that, in addition to already well characterized parameters (e.g., pH, and bile salt levels), significant differences in buffer capacity, surface tension, osmolality, and food components are observed pre-/postprandially. These differences should be reflected in test media to predict food effects on intralumenal performance of dosage forms.

Polymer Architecture and Drug Delivery

Abstract: Polymers occupy a major portion of materials used for controlled release formulations and drug-targeting systems because this class of materials presents seemingly endless diversity in topology and chemistry. This is a crucial advantage over other classes of materials to meet the ever-increasing requirements of new designs of drug delivery formulations. The polymer architecture (topology) describes the shape of a single polymer molecule. Every natural, seminatural, and synthetic polymer falls into one of categorized architectures: linear, graft, branched, cross-linked, block, star-shaped, and dendron/dendrimer topology. Although this topic spans a truly broad area in polymer science, this review introduces polymer architectures along with brief synthetic approaches for pharmaceutical scientists who are not familiar with polymer science, summarizes the characteristic properties of each architecture useful for drug delivery applications, and covers recent advances in drug delivery relevant to polymer architecture.

Theoretical and Practical Approaches for Prediction of Drug–Polymer Miscibility and Solubility

Abstract: Crystallization of drugs formulated in the amorphous form may lead to reduced apparent solubility, decreased rate of dissolution and bioavailability and compromise the physical integrity of the solid dosage form. The purpose of this work was to develop thermodynamic approaches, both practical and theoretical, that will yield a better understanding of which factors are most important for determining the ability of polymers to stabilize amorphous active pharmaceutical ingredients (API). Lattice based solution models were used to examine miscibility criteria in API-polymer blends. Different methods were used to estimate the Flory‐Huggins interaction parameter for model API-polymer systems consisting of felodipine or nifedipine with poly(vinylpyrrolidone) (PVP). These were melting point depression and determination of solubility parameters using group contribution theory. The temperature and enthalpy of fusion of crystalline API alone and the fusion temperature of the API in the presence of the polymer were measured by differential scanning calorimetry. The resultant thermal data were used to estimate the reduced driving force for crystallization and the solubility of the API in the polymer. Flory‐Huggins theory predicts that, for typical API-polymer systems, the entropy of mixing is always favorable and should be relatively constant. Due to the favorable entropy of mixing, miscibility can still be achieved in systems with a certain extent of unfavorable enthalpic interactions. For the model systems, interaction parameters derived from melting point depression were negative indicating that mixing was exothermic. Using these interaction parameters and Flory‐Huggins theory, miscibility was predicted for all compositions, in agreement with experimental data. A model was developed to estimate the solubility of the API in the polymer. The estimated solubility of the model APIs in PVP is low suggesting that kinetic rather than thermodynamic stabilization plays a significant role in inhibiting crystallization. The thermodynamics of API-polymer systems can be modeled using solution based theories. Such models can contribute towards providing an understanding of the compatibility between API and polymer and the mechanisms of physical stabilization in such systems.

Polymer Microneedles for Controlled-Release Drug Delivery

Abstract: As an alternative to hypodermic injection or implantation of controlled-release systems, this study designed and evaluated biodegradable polymer microneedles that encapsulate drug for controlled release in skin and are suitable for self-administration by patients. Arrays of microneedles were fabricated out of poly-lactide-co-glycolide using a mold-based technique to encapsulate model drugs—calcein and bovine serum albumin (BSA)—either as a single encapsulation within the needle matrix or as a double encapsulation, by first encapsulating the drug within carboxymethylcellulose or poly-l-lactide microparticles and then encapsulating drug-loaded microparticles within needles. By measuring failure force over a range of conditions, poly-lactide-co-glycolide microneedles were shown to exhibit sufficient mechanical strength to insert into human skin. Microneedles were also shown to encapsulate drug at mass fractions up to 10% and to release encapsulated compounds within human cadaver skin. In vitro release of calcein and BSA from three different encapsulation formulations was measured over time and was shown to be controlled by the encapsulation method to achieve release kinetics ranging from hours to months. Release was modeled using the Higuchi equation with good agreement (r 2 ≥ 0.90). After microneedle fabrication at elevated temperature, up to 90% of encapsulated BSA remained in its native state, as determined by measuring effects on primary, secondary, and tertiary protein structure. Biodegradable polymer microneedles can encapsulate drug to provide controlled-release delivery in skin for hours to months.

Biophysical and Structural Characterization of Polyethylenimine-Mediated siRNA Delivery in Vitro

Abstract: The goals of this study were as follows: 1) to evaluate the efficacy of different polyethylenimine (PEI) structures for siRNA delivery in a model system, and 2) to determine the biophysical and structural characteristics of PEI that relate to siRNA delivery. Biophysical characterization (effective diameter and zeta potential), cytotoxicities, relative binding affinities and in vitro transfection efficiencies were determined using nanocomplexes formed from PEI's of 800, 25,000, (both branched) and 22,000 (linear) molecular weights at varying N:P ratios and siRNA concentrations. The HR5-CL11 cell line stably expressing luciferase was used as a model system in vitro. Successful siRNA delivery was observed within a very narrow window of conditions, and only with the 25,000 branched PEI at an N:P ratio of 6:1 and 8:1 and with 200 nM siRNA. While the zeta potential and size of PEI:siRNA complexes correlated to transfection efficacy in some cases, complex stability may also affect transfection efficacy. The ability of PEI to transfer functionally active siRNA to cells in culture is surprisingly dependent on its biophysical and structural characteristics when compared to its relative success and ease of use for DNA delivery.

Why is it challenging to predict intestinal drug absorption and oral bioavailability in human using rat model.

Abstract: To study the correlation of intestinal absorption for drugs with various absorption routes between human and rat, and to explore the underlying molecular mechanisms for the similarity in drug intestinal absorption and the differences in oral bioavailability between human and rat. The intestinal permeabilities of 14 drugs and three drug-like compounds with different absorption mechanisms in rat and human jejunum were determined by in situ intestinal perfusion. A total of 48 drugs were selected for oral bioavailability comparison. Expression profiles of transporters and metabolizing enzymes in both rat and human intestines (duodenum and colon) were measured using GeneChip analysis. No correlation (r 2 = 0.29) was found in oral drug bioavailability between rat and human, while a correlation (r 2 = 0.8) was observed for drug intestinal permeability with both carrier-mediated absorption and passive diffusion mechanisms between human and rat small intestine. Moderate correlation (with r 2 > 0.56) was also found for the expression levels of transporters in the duodenum of human and rat, which provides the molecular mechanisms for the similarity and correlation of drug absorption between two species. In contrast, no correlation was found for the expressions of metabolizing enzymes between rat and human intestine, which indicates the difference in drug metabolism and oral bioavailability in two species. Detailed analysis indicates that many transporters (such as PepT1, SGLT-1, GLUT5, MRP2, NT2, and high affinity glutamate transporter) share similar expression levels in both human and rat with regional dependent expression patterns, which have high expression in the small intestine and low expression in the colon. However, discrepancy was also observed for several other transporters (such as MDR1, MRP3, GLUT1, and GLUT3) in both the duodenum and colon of human and rat. In addition, the expressions of metabolizing enzymes (CYP3A4/CYP3A9 and UDPG) showed 12 to 193-fold difference between human and rat intestine with distinct regional dependent expression patterns. The data indicate that rat and human show similar drug intestinal absorption profiles and similar transporter expression patterns in the small intestine, while the two species exhibit distinct expression levels and patterns for metabolizing enzymes in the intestine. Therefore, a rat model can be used to predict oral drug absorption in the small intestine of human, but not to predict drug metabolism or oral bioavailability in human.

Culture of Calu-3 cells at the air interface provides a representative model of the airway epithelial barrier.

Abstract: The aim of this study was to compare the effect of liquid-covered culture (LCC) and air-interfaced culture (AIC) on Calu-3 cell layer morphology and permeability, thus assessing the fitness of these culture systems as models of airway epithelium barrier function. Cell layers were grown on 0.33 cm2 Transwell polyester cell culture supports. Cell layers grown using LCC and AIC were evaluated by using light and electron microscopy, transepithelial electrical resistance (TER), and permeability to the transepithelial flux of fluorescein sodium (flu-Na), and by varying molecular weight dextrans labeled with fluorescein isothiocyanate (FITC-dex). The tight junction protein, zona occludens protein-1 (ZO-1), was visualized by confocal microscopy and apical glycoprotein secretions were identified by using alcian blue. Cells grown via AIC produced a more columnar epithelium with a more rugged apical topography and greater glycoprotein secretion compared to cells grown via LCC. Apical protrusions appearing to be cilia-like structures were observed on occasional cells using AIC, but typical airway ciliated cell phenotypes were not produced under either condition. Secretory granules were observed in cells cultured under both conditions. Cells cultured using LCC exhibited higher levels of ZO-1 protein than the AIC counterpart. The maximal TER of cells using LCC, 1,086 ± 113 Ω cm2 at 11–16 days, was significantly greater than the TER of cells cultured using AIC, 306 ± 53 Ω cm2 at 11–13 days. Apparent permeability (P app ) values for the transport of flu-Na using LCC and AIC were 1.48 ± 0.19×10−7 and 3.36 ± 0.47×10−7 cm s−1, respectively. Transport rates of flu-Na and FITC-dex were inversely proportional to molecular weight, and were significantly lower (p < 0.05) in cell layers grown using LCC than AIC. Renkin analysis fitted the data to single pore populations of radii 7.7 and 11.0 nm for LCC and AIC, respectively. Distinct differences in morphology and permeability result when Calu-3 cells are grown using AIC or LCC. Cells cultured using AIC generate a model more morphologically representative of the airway epithelium than cells cultured using LCC.

Electrospun micro- and nanofibers for sustained delivery of paclitaxel to treat C6 glioma in vitro.

Abstract: The present study aims to develop electrospun PLGA-based micro- and nanofibers as implants for the sustained delivery of anticancer drug to treat C6 glioma in vitro. PLGA and an anticancer drug—paclitaxel-loaded PLGA micro- and nanofibers were fabricated by electrospinning and the key processing parameters were investigated. The physical and chemical properties of the micro- and nanofibers were characterized by various state-of-the-art techniques, such as scanning electron microscope and field emission scanning electron microscope for morphology, X-ray photoelectron spectroscopy for surface chemistry, gel permeation chromatogram for molecular weight measurements and differential scanning calorimeter for drug physical status. The encapsulation efficiency and in vitro release profile were measured by high performance liquid chromatography. In addition, the cytotoxicity of paclitaxel-loaded PLGA nanofibers was evaluated using 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide MTT) assay on C6 glioma cell lines. PLGA fibers with diameters of around several tens nanometers to 10 μm were successfully obtained by electrospinning. Ultrafine fibers of around 30 nm were achieved after addition of organic salts to dilute polymer solution. The encapsulation efficiency for paclitaxel-loaded PLGA micro- and nanofibers was more than 90%. DSC results suggest that the drug was in the solid solution state in the polymeric micro- and nanofibers. In vitro release profiles suggest that paclitaxel sustained release was achieved for more than 60 days. Cytotoxicity test results suggest that IC50 value of paclitaxel-loaded PLGA nanofibers (36 μg/ml, calculated based on the amount of paclitaxel) is comparable to the commercial paclitaxel formulation-Taxol®. Electrospun paclitaxel-loaded biodegradable micro- and nanofibers may be promising for the treatment of brain tumour as alternative drug delivery devices.

Application of Micro- and Nano-Electromechanical Devices to Drug Delivery

Abstract: Micro- and nano-electromechanical systems (MEMS and NEMS)-based drug delivery devices have become commercially-feasible due to converging technologies and regulatory accommodation. The FDA Office of Combination Products coordinates review of innovative medical therapies that join elements from multiple established categories: drugs, devices, and biologics. Combination products constructed using MEMS or NEMS technology offer revolutionary opportunities to address unmet medical needs related to dosing. These products have the potential to completely control drug release, meeting requirements for on-demand pulsatile or adjustable continuous administration for extended periods. MEMS or NEMS technologies, materials science, data management, and biological science have all significantly developed in recent years, providing a multidisciplinary foundation for developing integrated therapeutic systems. If small-scale biosensor and drug reservoir units are combined and implanted, a wireless integrated system can regulate drug release, receive sensor feedback, and transmit updates. For example, an "artificial pancreas" implementation of an integrated therapeutic system would improve diabetes management. The tools of microfabrication technology, information science, and systems biology are being combined to design increasingly sophisticated drug delivery systems that promise to significantly improve medical care.

Metrics for External Model Evaluation with an Application to the Population Pharmacokinetics of Gliclazide

Abstract: Purpose The aim of this study is to define and illustrate metrics for the external evaluation of a population model.

A new polymer-lipid hybrid nanoparticle system increases cytotoxicity of doxorubicin against multidrug-resistant human breast cancer cells.

Abstract: This work is intended to develop and evaluate a new polymer–lipid hybrid nanoparticle system that can efficiently load and release water-soluble anticancer drug doxorubicin hydrochloride (Dox) and enhance Dox toxicity against multidrug-resistant (MDR) cancer cells. Cationic Dox was complexed with a new soybean-oil-based anionic polymer and dispersed together with a lipid in water to form Dox-loaded solid lipid nanoparticles (Dox–SLNs). Drug loading and release properties were measured spectrophotometrically. The in vitro cytotoxicity of Dox–SLN and the excipients in an MDR human breast cancer cell line (MDA435/LCC6/MDR1) and its wild-type line were evaluated by trypan blue exclusion and clonogenic assays. Cellular uptake and retention of Dox were determined with a microplate fluorometer. Dox–SLNs were prepared with a drug encapsulation efficiency of 60–80% and a particle size range of 80–350 nm. About 50% of the loaded drug was released in the first few hours and an additional 10–20% in 2 weeks. Treatment of the MDR cells with Dox–SLN resulted in over 8-fold increase in cell kill when compared to Dox solution treatment at equivalent doses. The blank SLN and the excipients exhibited little cytotoxicity. The biological activity of the released Dox remained unchanged from fresh, free Dox. Cellular Dox uptake and retention by the MDR cells were both significantly enhanced (p < 0.05) when Dox was delivered in Dox–SLN form. The new polymer–lipid hybrid nanoparticle system is effective for delivery of Dox and enhances its efficacy against MDR breast cancer cells.

Analysis of amorphous and nanocrystalline solids from their X-ray diffraction patterns.

Abstract: The purpose of this paper is to provide a physical description of the amorphous state for pharmaceutical materials and to investigate the pharmaceutical implications. Techniques to elucidate structural differences in pharmaceutical solids exhibiting characteristic X-ray amorphous powder patterns are also presented. The X-ray amorphous powder diffraction patterns of microcrystalline cellulose, indomethacin, and piroxicam were measured with laboratory XRPD instrumentation. Analysis of the data were carried out using a combination of direct methods, such as pair distribution functions (PDF), and indirect material modeling techniques including Rietveld, total scattering, and amorphous packing. The observation of X-ray amorphous powder patterns may indicate the presence of amorphous, glassy or disordered nanocrystalline material in the sample. Rietveld modeling of microcrystalline cellulose (Avicel® PH102) indicates that it is predominantly disordered crystalline cellulose Form Iβ with some amorphous contribution. The average crystallite size of the disordered nanocrystalline cellulose was determined to be 10.9 nm. Total scattering modeling of ground samples of α, γ, and δ crystal forms of indomethacin in combination with analysis of the PDFs provided a quantitative picture of the local structure during various stages of grinding. For all three polymorphs, with increased grinding time, a two-phase system, consisting of amorphous and crystalline material, continually transformed to a completely random close packed (RCP) amorphous structure. The same pattern of transformation was detected for the Form I polymorph of piroxicam. However, grinding of Form II of piroxicam initially produced a disordered phase that maintained the local packing of Form II but over a very short nanometer length scale. The initial disordered phase is consistent with continuous random network (CRN) glass material. This initial disordered phase was maintained to a critical point when a transition to a completely amorphous RCP structure occurred. Treating X-ray amorphous powder patterns with different solid-state models, ranging from disordered nanocrystalline to glassy and amorphous, resulted in the assignment of structures in each of the systems examined. The pharmaceutical implications with respect to the stability of the solid are discussed.

Metabonomics techniques and applications to pharmaceutical research & development.

Abstract: In this review, the background to the approach known as metabonomics is provided, giving a brief historical perspective and summarizing the analytical and statistical techniques used. Some of the major applications of metabonomics relevant to pharmaceutical Research & Development are then reviewed including the study of various influences on metabolism, such as diet, lifestyle, and other environmental factors. The applications of metabonomics in drug safety studies are explained with special reference to the aims and achievements of the Consortium for Metabonomic Toxicology. Next, the role that metabonomics might have in disease diagnosis and therapy monitoring is provided with some examples, and the concept of pharmacometabonomics as a way of predicting an individual's response to treatment is highlighted. Some discussion is given on the strengths and weaknesses, opportunities of, and threats to metabonomics.

A Comparison of the Physical Stability of Amorphous Felodipine and Nifedipine Systems

Abstract: Purpose The objective of this study was to investigate thermodynamic and kinetic factors contributing to differences in the isothermal nucleation rates of two structurally related calcium channel blockers, nifedipine and felodipine, both alone and in the presence of poly(vinylpyrrolidone) (PVP).

Methods to Assess in Vitro Drug Release from Injectable Polymeric Particulate Systems

Abstract: This review provides a compilation of the methods used to study real-time (37°C) drug release from parenteral microparticulate drug delivery systems administered via the subcutaneous or intramuscular route. Current methods fall into three broad categories, viz., sample and separate, flow-through cell, and dialysis techniques. The principle of the specific method employed along with the advantages and disadvantages are described. With the “sample and separate” technique, drug-loaded microparticles are introduced into a vessel, and release is monitored over time by analysis of supernatant or drug remaining in the microspheres. In the “flow-through cell” technique, media is continuously circulated through a column containing drug-loaded microparticles followed by analysis of the eluent. The “dialysis” method achieves a physical separation of the drug-loaded microparticles from the release media by use of a membrane, which allows for sampling without interference of the microspheres. With all these methods, the setup and sampling techniques seem to influence in vitro release; the results are discussed in detail, and criteria to aid in selection of a method are stated. Attempts to establish in vitro–in vivo correlation for these injectable dosage forms are also discussed. It would be prudent to have an in vitro test method for microparticles that satisfies compendial and regulatory requirements, is user friendly, robust, and reproducible, and can be used for quality-control purposes at real-time and elevated temperatures.

Oral Absorption of Poorly Water-Soluble Drugs: Computer Simulation of Fraction Absorbed in Humans from a Miniscale Dissolution Test

Abstract: The purpose of this study was to develop a new system for computer simulation to predict fraction absorbed (F a ) of Biopharmaceutical Classification System (BCS) class II (low solubility–high permeability) drugs after oral administration to humans, from a miniscale dissolution test. Human oral absorption of 12 lipophilic drugs was simulated theoretically by using the dissolution and permeation parameters of the drugs. A miniscale dissolution test and a solubility study were carried out in a conventional buffer and a biorelevant medium (pH 6.5). A dissolution parameter, which can simulate in vivo dissolution, was obtained from the in vitro dissolution curve. Human intestinal permeability was estimated assuming that the permeation was limited by diffusion through the unstirred water layer. The F a in humans was predicted and then compared with clinical data. The dissolution and solubility of most model drugs were faster and higher in a biorelevant medium than in a conventional buffer. The simulated absorption was limited by the drug dissolution rate and/or solubility. Predicted F a was significantly correlated with clinical data (correlation coefficient r 2 = 0.82, p < 0.001) when the dissolution profiles in biorelevant medium were used for the simulation. This new system quantitatively simulated human absorption and would be beneficial for the prediction of human F a values for BCS class II drugs.

Enhanced oral paclitaxel bioavailability after administration of paclitaxel-loaded lipid nanocapsules.

Abstract: The aim of this study was to evaluate the pharmacokinetics of paclitaxel-loaded lipid nanocapsules (LNC) in rats to assess the intrinsic effect of the dosage form on the improvement of paclitaxel oral exposure. Paclitaxel-loaded LNC were prepared and characterized in terms of size distribution, drug payload, and the kinetics of paclitaxel crystallization. Taxol®, Taxol® with verapamil, or paclitaxel-loaded LNC were administered orally to rats. The plasma concentration of paclitaxel was determined using liquid chromatography mass spectrometry. The average size of LNC was 60.9 ± 1.5 nm. The drug payload of paclitaxel was 1.91 ± 0.01 mg/g of aqueous dispersion. The encapsulation efficiency was 99.9 ± 1.0%, and 1.7 ± 0.1% of paclitaxel was crystallized after 24 h. The oral bioavailability of Taxol® alone was 6.5%. After oral administration of paclitaxel-loaded LNC or paclitaxel associated with verapamil, the area under the plasma concentration–time curve was significantly increased (about 3-fold) in comparison to the control group (p < 0.05). The results indicated that LNC provided a promising new formulation to enhance the oral bioavailability of paclitaxel while avoiding the use of pharmacologically active P-gp inhibitors, such as verapamil.

CYP Induction-Mediated Drug Interactions: in Vitro Assessment and Clinical Implications

Abstract: Cytochrome P450 (CYP) induction-mediated interaction is one of the major concerns in clinical practice and for the pharmaceutical industry. There are two major issues associated with CYP induction: a reduction in therapeutic efficacy of comedications and an induction in reactive metabolite-induced toxicity. Because CYP induction is a metabolic liability in drug therapy, it is highly desirable to develop new drug candidates that are not potent CYP inducer to avoid the potential of CYP induction-mediated drug interactions. For this reason, today, many drug companies routinely include the assessment of CYP induction at the stage of drug discovery as part of the selection processes of new drug candidates for further clinical development. The purpose of this article is to review the molecular mechanisms of CYP induction and the clinical implications, including pharmacokinetic and pharmacodynamic consequences. In addition, factors that affect the degree of CYP induction and extrapolation of in vitro CYP induction data to in vivo situations will also be discussed. Finally, assessment of the potential of CYP induction at the drug discovery and development stage will be discussed.

Design of Estradiol Loaded PLGA Nanoparticulate Formulations: A Potential Oral Delivery System for Hormone Therapy

Abstract: Estradiol (E2), a highly lipophilic molecule with good oral absorption but poor oral bioavailability, was incorporated into poly(lactide-co-glycolide) (PLGA) nanoparticles to improve its oral bioavailability. Nanoparticles were prepared by using polyvinyl alcohol (PVA) or didodecyldimethylammonium bromide (DMAB) as stabilizer, leading to negatively (size 410.9 ± 39.4 nm) and positively (size 148.3 ± 10.7 nm) charged particles, respectively. Both preparations showed near zero order release in vitro with about 95% drug being released within 45 and 31 days for PVA and DMAB, respectively. In situ intestinal uptake studies in male Sprague–Dawley (SD) rats showed higher uptake of DMAB stabilized nanoparticles. Following oral administration to male SD rats, E2 could be detected in blood for 7 and 2 days from DMAB and PVA stabilized nanoparticles, respectively. Histopathological examination and blood counts indicated the absence of inflammatory response. These data suggest that DMAB stabilized PLGA nanoparticles have great potential as carriers for oral delivery of estradiol.

Cocrystal Formation during Cogrinding and Storage is Mediated by Amorphous Phase

Abstract: Purpose The purpose of this work was to investigate the mechanisms of cocrystal formation during cogrinding and storage of solid reactants, and to establish the effects of water by cogrinding with hydrated form of reactants and varying RH conditions during storage.

Microinfusion Using Hollow Microneedles

Abstract: The aim of the study is to determine the effect of experimental parameters on microinfusion through hollow microneedles into skin to optimize drug delivery protocols and identify rate-limiting barriers to flow. Glass microneedles were inserted to a depth of 720–1080 μm into human cadaver skin to microinfuse sulforhodamine solution at constant pressure. Flow rate was determined as a function of experimental parameters, such as microneedle insertion and retraction distance, infusion pressure, microneedle tip geometry, presence of hyaluronidase, and time. Single microneedles inserted into skin without retraction were able to infuse sulforhodamine solution into the skin at flow rates of 15–96 μl/h. Partial retraction of microneedles increased flow rate up to 11.6-fold. Infusion flow rate was also increased by greater insertion depth, larger infusion pressure, use of a beveled microneedle tip, and the presence of hyaluronidase such that flow rates ranging from 21 to 1130 μl/h were achieved. These effects can be explained by removing or overcoming the large flow resistance imposed by dense dermal tissue, compressed during microneedle insertion, which blocks flow from the needle tip. By partially retracting microneedles after insertion and other methods to overcome flow resistance of dense dermal tissue, protocols can be designed for hollow microneedles to microinfuse fluid at therapeutically relevant rates.

The influence of fine excipient particles on the performance of carrier-based dry powder inhalation formulations.

Abstract: The inclusion of a small amount of fine particle excipient in a carrier-based dry powder inhalation system is a well researched technique to improve formulation performance and is employed in the pharmaceutical industry. The removal of intrinsic fines from a lactose carrier has been found to decrease formulation performance, whereas adding fines of many different materials into formulations increased performance. Changing the particle size of these fines, the amount added and the technique by which they were prepared also affected formulation behaviour. Despite this body of research, there is disagreement as to the mechanism by which fines improved formulation performance, with two main hypotheses presented in the literature. The first hypothesis suggested that fines prevent the drug from adhering to the strongest binding sites on the carrier, whilst the second proposed that fine particles of drug and excipient form mixed agglomerates that are more easily dispersed and deaggregated during aerosolisation. The evidence in support of each hypothesis is limited and it is clear that future research should aim to produce stronger mechanistic evidence. The investigation of interparticulate interactions using techniques such as atomic force microscopy and inverse gas chromatography may prove useful in achieving this aim.

Use of a dynamic in vitro lipolysis model to rationalize oral formulation development for poor water soluble drugs: correlation with in vivo data and the relationship to intra-enterocyte processes in rats.

Abstract: To examine the correlation between the in vitro solubilization process of lipophilic compounds from different lipid solutions and the corresponding in vivo oral bioavailability data. In particular, to assess the influence of intra-enterocyte processes (metabolism and lymphatic absorption) on this correlation. The dissolution of progesterone and vitamin D3 in long (LCT), medium (MCT) and short (SCT) chain triglyceride solutions were tested in a dynamic in vitro lipolysis model. The absolute oral bioavailability of the drugs from the tested formulations was investigated in rats. Vitamin D3 bioavailability was also examined following lymphatic transport blockage induced by cycloheximide (3 mg/kg). The dynamic in vitro lipolysis experiments indicated a rank order of MCT > LCT > SCT for both progesterone and vitamin D3. The bioavailability of progesterone correlated with the in vitro data, despite its significant pre-systemic metabolism. For vitamin D3, an in vivo performance rank order of LCT > MCT > SCT was obtained. However, when the lymphatic transport was blocked the bioavailability of vitamin D3 correlated with in vitro data. The in vitro lipolysis model is useful for optimization of oral lipid formulations even in the case of pre-systemic metabolism in the gut. However, when lymphatic transport is a significant route of absorption, the in vitro lipolysis data may not be predictive for actual in vivo absorption.

Surface crystallization of indomethacin below Tg.

Abstract: Purpose To study the surface crystallization of indomethacin (IMC) below Tg and its effects on the kinetics of overall crystallization.

Lipid injectable emulsions: Pharmacopeial and safety issues.

Abstract: Lipid injectable emulsions have been routinely used in patients worldwide for over 40 years as a nutritional supplement in patients requiring parenteral nutrition. They can be given as a separate infusion or added into total parenteral nutrition admixtures. Despite such broad use, no pharmacopeial standards exist with respect to the optimal pharmaceutical characteristics of the formulation. Several attempts to establish standard physical and chemical attributes have been attempted by various pharmacopeias around the world, but without success largely due to technical issues regarding the creation of globule size limits. Recently, the United States Pharmacopeia has revised its previous efforts and developed two methods and criteria (under Chapter ) to measure the mean droplet size (Method I), and the large-diameter tail > 5 μm (Method II) of the globule size distribution to verify the stability of lipid injectable emulsions. Importantly, it is the latter size limits of Method II that have the greatest implications for infusion safety. The major safety issues involving lipid injectable emulsions include impairments in plasma clearance in susceptible patients, and the infusion of an unstable emulsion containing large quantities of potentially embolic fat globules. Recent animal studies investigating the toxicity from the infusion of unstable lipid injectable emulsions have shown evidence of oxidative stress and tissue damage to the liver when recommended globule size limits determined by Method II of the USP are exceeded. Adoption of Chapter of the USP seems appropriate at this time.