Particle size reduction for improvement of oral bioavailability of hydrophobic drugs: I. Absolute oral bioavailability of nanocrystalline danazol in beagle dogs

Dissolution-rate enhancement of fenofibrate by adsorption onto silica using supercritical carbon dioxide

Dissolution rate of a poorly water-soluble drug, fenofibrate, is increased by adsorbing the drug onto silica. The adsorption is achieved by first dissolving the drug in supercritical carbon dioxide and then depressurizing the solution onto silica. Loadings of up to 27.5 wt.% drug onto silica are obtained. Since solvents are not used in the loading process, the fenofibrate/silica formulation is free of any residual solvent, and carbon dioxide is freely removed upon depressurization. The formulation is characterized using infrared spectroscopy, ultraviolet spectroscopy, X-ray diffraction, differential scanning calorimetry and scanning electron microscopy. Based on in vitro dissolution study, a significant increase in the dissolution rate (approximately 80% drug release in 20 min) of drug-silica formulation is observed as compared to micronized fenofibrate (approximately 20% drug release in 20 min), which can be attributed to increase in the surface area and decrease in the crystallinity of drug after adsorption onto silica. Two different formulations are compared: (A) amorphous fenofibrate/silica and (B) slightly crystalline fenofibrate/silica. The second formulation is found to be more stable on storage.

Cyclodextrins

beta-cyclodextrin (beta-CD) and other cyclodextrins (CDs) have utility for solubilizing and stabilizing drugs; however, some are nephrotoxic when administered parenterally. A number of workers have attempted to identify, prepare, and evaluate various CD derivatives with superior inclusion complexation and maximal in vivo safety for various biomedical uses. A systematic study led to SBE-beta-CD (Captisol), a polyanionic variably substituted sulfobutyl ether of beta-CD, as a non-nephrotoxic derivative and HP-beta-CD, a modified CD developed by Janssen. SBE-beta-CD and HP-beta-CD have undergone extensive safety studies and are currently used in six products approved by the Food and Drug Administration (four for Captisol and two for HP-beta-CD). They are also in use in numerous clinical and preclinical studies. This article will focus on the issues that led to the development of these two CDs, their safety, characterization, and applications, and especially their ability to improve drug delivery. SBE-beta-CD interacts very well with neutral drugs to facilitate solubility and chemical stability, and because of its polyanionic nature, it interacts particularly well with cationic drugs. Complexes between SBE-beta-CD and HP-beta-CD and various drugs have been shown to rapidly dissociate after parenteral drug administration, to have no tissue-irritating effects after intramuscular dosing, and to result in superior oral bioavailability of poorly water-soluble drugs. The pharmacokinetics, tissue distribution, and cellular effects of some representative CDs, including SBE-beta-CD and HP-beta-CD, are reviewed. The safety profiles of CDs are discussed, with emphasis on the biological effects of some CDs on the gastrointestinal tract, kidney, and reproduction and development and the carcinogenic potential of CDs. In addition, human experience with CD derivatives, specifically SBE-beta-CD and HP-beta-CD, indicates that these two CDs are well tolerated in humans and have no adverse effects on the kidneys or other organs following either oral or intravenous administration.

In vivo assessment of oral administration of probucol nanoparticles in rats

Pharmacokinetic profiles of probucol were evaluated after oral administration of the various nanosuspensions in rats. Probucol nanoparticles were prepared by co-grinding with various molecular weights of polyvinylpyrrolidone (PVP K12, PVP K17 and PVP K30) and sodium dodecyl sulfate (SDS). The average particle sizes of probucol after dispersing the ternary ground mixtures (GMs), probucol/PVP K12/SDS, probucol/PVP K17/SDS and probucol/PVP K30/SDS into water were 28, 75 and 89 nm respectively. The ternary GM suspensions with PVP K17/SDS and PVP K30/SDS were stable at 25 degrees C. However the particle size of probucol from the ternary GM with PVP K12/SDS gradually increased. Pharmacokinetic profiles of probucol indicated that variation in particle surface condition covered with PVP and SDS in addition to the particle size affected the improvement of in vivo absorption of probucol. The ternary GM with PVP K12/SDS exhibited a superior improvement of probucol absorption compared to the GMs with PVP K17/SDS and PVP K30/SDS. The binary GM with PVP or SDS and physical mixtures with PVP and/or SDS did not show significant differences in the area under the plasma concentration-time curve compared to the unprocessed probucol. In conclusion, preparation of probucol nanoparticles by co-grinding with PVP K12 and SDS could be a promising method for bioavailability enhancement.

Past and future evolution in colloidal drug delivery systems

Colloidal drug delivery systems have been providing alternative formulation approaches for problematic drug candidates, and improved delivery for existing compounds for decades. Colloidal systems for drug delivery have all evolved down a similar pathway, almost irrespective of the delivery system, from conception, to the use of safer excipients, PEGylation for passive targeting and attachment of ligands for active targeting. The recent emergence of truly biologically interactive systems represents the latest step forward in colloidal delivery systems. In this article, the maturation pathway and recent advances for the major classes of colloidal delivery systems are reviewed, and the paper poses the question of whether the nanotechnology boom will create a revolution in colloidal delivery, or just the next natural stage in evolution.

Oral delivery of 1,3-dicyclohexylurea nanosuspension enhances exposure and lowers blood pressure in hypertensive rats

Cytochrome P450-derived epoxyeicosatrienoic acids (EET) are biologically active metabolites of arachidonic acid that have potent effects on renal vascular reactivity and tubular ion transport and have been implicated in the control of blood pressure. EETs are hydrolyzed to their less active diols, dihydroxyeicosatrienoic acids (DHET), by the enzyme soluble epoxide hydrolase (sEH). 1,3-dicyclohexylurea (DCU), a potent sEH inhibitor, lowers systemic blood pressure in spontaneously hypertensive rats when dosed intraperitoneally. However, DCU has poor aqueous solubility, posing a challenge for in vivo oral delivery. To overcome this limitation, we formulated DCU in a nanosuspension using wet milling. Milling reduced particle size, increasing the total surface area by approximately 40-fold. In rats chronically infused with angiotensin II, the DCU nanosuspension administered orally twice daily for 4 days produced plasma exposures an order of magnitude greater than unmilled DCU and lowered blood pressure by nearly 30 mmHg. Consistent with the mechanism of sEH inhibition, DCU increased plasma 14,15-EET and decreased plasma 14,15-DHET levels. These data confirm the antihypertensive effect of sEH inhibition and demonstrate that greatly enhanced exposure of a low-solubility compound is achievable by oral delivery using a nanoparticle drug delivery system.

Particle design of poorly water-soluble drug substances using supercritical fluid technologies

In order to improve the dissolution properties of poorly water-soluble drugs, some drugs were subjected to micronization or prepared as composite particles using supercritical fluid (SCF) technology with carbon dioxide (CO(2)). Solubility in CO(2) is the key when using this method. Solubility affects the supersaturation of the materials in the solvent as well as the mass transfer of that solvent, which are both critical to the micronization of the materials and the formation of the composite particles. Some useful techniques that can be used to avoid the problems posed by the characteristics of the drug itself are combining SC-CO(2) with other technologies, such as the formation of coacervates or emulsions, and other equipment types, such as milling or ultrasound fields. Another advantage of SCF technology is that it is considered to be green chemistry. SC-CO(2) can improve the solubility of poorly water-soluble drug substances using few or no organic solvents and with little or no heating.

Cogrinding enhances the oral bioavailability of EMD 57033, a poorly water soluble drug, in dogs

The oral bioavailability of EMD 57033, a calcium sensitizing agent with poor solubility, was compared in dogs using four solid dosage form formulation approaches: a physical blend of the drug with excipients, micronization of the drug, preparation of coground mixtures and spray-drying of the drug from a nanocrystalline suspension. The formulations contained generally accepted excipients such as lactose, hydroxypropylmethyl cellulose and sodium lauryl sulphate in usual quantities. Drug micronization and cogrinding was realized by a jet-milling technique. Nanoparticles were created by media milling using a bead mill. All formulations were administered orally as dry powders in hard gelatine capsules. While micronization increased the absolute bioavailability of the solid drug significantly compared to crude material (from nondetectable to 20%), cogrinding with specific excipients was able to almost double this improvement (up to 39%). With an absolute bioavailability of 26%, spray-dried nanoparticular EMD 57033 failed to show the superior bioavailability that had been anticipated from in vitro data. The control solution prepared with cyclodextrin was shown to have an absolute bioavailability of 57% (vs. i.v. infusion). It was concluded that cogrinding can be a useful tool to improve the bioavailability of poorly soluble drugs from a solid dosage form format.

Dissolution improvement of four poorly water soluble drugs by cogrinding with commonly used excipients

The rate of the dissolution of four poorly soluble drugs (EMD 57033, albendazole, danazol and felodipine) was improved by cogrinding them with various excipients (lactose monohydrate, corn starch, polyvinylpyrrolidone, hydroxypropylmethyl cellulose and sodium lauryl sulphate) using a jet-milling technique. Solid state characterization studies by X-ray diffraction and differential scanning calorimetry verified the maintenance of the crystalline state of the active substances after milling. In vitro dissolution of the coground mixtures in biorelevant media was much faster than from micronised drug in the corresponding physical mixtures for all four compounds. Supersaturated solutions were generated in some cases (EMD 50733 and felodipine), but this phenomenon appeared to be drug- and excipient-specific. Cogrinding with lactose monohydrate resulted in fast dissolution with unstable supersaturation for EMD 57033. Cogrinding the same drug with PVP or HPMC produced a more sustained supersaturation. SLS accelerated the dissolution of EMD 50733 but inhibited supersaturation. The results suggest that the cogrinding with selected excipients is a powerful tool to accelerate the dissolution of poorly soluble drugs without converting the drug to the amorphous form or changing the particle size.

Dissolution enhancement of fenofibrate by micronization, cogrinding and spray-drying: Comparison with commercial preparations

Several techniques were compared for improving the dissolution of fenofibrate, a poorly soluble drug. Particle size reduction was realized by jet milling (micronization; cogrinding with lactose, polyvinylpyrrolidone or sodium lauryl sulphate) and by media milling using a bead mill (nanosizing) with subsequent spray-drying. Solid state characterization by X-ray diffraction and Differential Scanning Calorimetry verified the maintenance of the crystalline state of the drug after dry milling and its conversion to the amorphous state during spray-drying. Micronization of fenofibrate enhanced its dissolution rate in biorelevant media (8.2% in 30min) compared to crude material (1.3% in 30min). Coground mixtures of the drug increased the dissolution rate further (up to 20% in 30min). Supersaturated solutions were generated by nanosizing combined with spray-drying, this process converted fenofibrate to the amorphous state. Fenofibrate drug products commercially available on the German and French markets dissolved similarly to crude or micronized fenofibrate, but significantly slower than the coground or spray-dried fenofibrate mixtures. The results suggest that cogrinding and spray-drying are powerful techniques for the preparation of rapidly dissolving formulations of fenofibrate, and could potentially lead to improvements in the bioavailability of oral fenofibrate products.

Nanoparticles formulation of Cuscuta chinensis prevents acetaminophen-induced hepatotoxicity in rats

Cuscuta chinensis is a commonly used traditional Chinese medicine to nourish the liver and kidney. Due to the poor water solubility of its major constituents such as flavonoids and lignans, its absorption upon oral administration could be limited. The purpose of the present study was to use the nanosuspension method to prepare C. chinensis nanoparticles (CN), and to compare the hepatoprotective and antioxidant effects of C. chinensis ethanolic extract (CE) and CN on acetaminophen-induced hepatotoxicity in rats. An oral dose of CE at 125 and 250 mg/kg and CN at 25 and 50mg/kg showed a significant hepatoprotective effect relatively to the same extent (P<0.05) by reducing levels of aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase. These biochemical assessments were supported by rat hepatic biopsy examinations. In addition, the antioxidant activities of CE and CN both significantly increased superoxide dismutase, catalase, glutathione peroxidase, and reduced malondialdehyde (P<0.05). Moreover, the results also indicated that the hepatoprotective and antioxidant effects of 50 mg/kg CN was effectively better than 125 mg/kg CE (P<0.05), and an oral dose of CN that is five times as less as CE could exhibit similar levels of outcomes. In conclusion, we suggest that the nanoparticles system can be applied to overcome other water poorly soluble herbal medicines and furthermore to decrease the treatment dosage.

Drug Nanoparticles: Formulating Poorly Water-Soluble Compounds

More than 40% of compounds identified through combinatorial screening programs are poorly soluble in water. These molecules are difficult to formulate using conventional approaches and are associated with innumerable formulation-related performance issues. Formulating these compounds as pure drug nanoparticles is one of the newer drug-delivery strategies applied to this class of molecules. Nanoparticle dispersions are stable and have a mean diameter of less than 1 micron. The formulations consist of water, drug, and one or more generally regarded as safe excipients. These liquid dispersions exhibit an acceptable shelf-life and can be postprocessed into various types of solid dosage forms. Drug nanoparticles have been shown to improve bioavailability and enhance drug exposure for oral and parenteral dosage forms. Suitable formulations for the most commonly used routes of administration can be identified with milligram quantities of drug substance, providing the discovery scientist with an alternate avenue for screening and identifying superior analogs. For the toxicologist, the approach provides a means for dose escalation using a formulation that is commercially viable. In the past few years, formulating poorly water-soluble compounds using a nanoparticulate approach has evolved from a conception to a realization whose versatility and applicability are just beginning to be realized.

Effect of polymer molecular weight on the production of drug nanoparticles

Stable, polymer-coated nanoparticles of two hydrophobic drugs, namely nabumetone and halofantrine, have been prepared by a wet-bead milling process performed in the presence of a stabilizing homopolymer, either hydroxypropylmethylcellulose (HPMC) or polyvinylpyrrolidone (PVP), of differing molecular weights and concentrations. Although nabumetone nanoparticles could only be produced when HPMC was used as stabilizing polymer, halofantrine nanoparticles could be prepared using either HPMC or PVP. Stable nanoparticles of nabumetone could be produced using a HPMC solution of viscosity average molecular weight, M(v), of 5 kg/mol over an approximate four fold polymer concentration range (0.63-2.5% w/w) when a drug loading of 20% w/w was used. Increasing the molecular weight of HPMC up to a limiting M(v) of 89 kg/mol did not result in the formation of nanoparticles at any of the polymer concentrations examined. The amount of polymer absorbed onto the nanoparticles was determined by measuring the depletion of polymer from solution based on either an ultra-violet (PVP) or optical rotatory dispersion (ORD) (HPMC) assay. The slightly lower concentration of HMPC found to be present on the surface of the halofantrine nanoparticles compared with the nabumetone nanoparticles suggested a differing affinity of the polymer for the surface of the two drugs.

Prediction of human pharmacokinetics--gastrointestinal absorption

Permeability (P(e)) and solubility/dissolution are two major determinants of gastrointestinal (GI) drug absorption. Good prediction of these is crucial for predicting doses, exposures and potential interactions, and for selecting appropriate candidate drugs. The main objective was to evaluate screening methods for prediction of GI P(e), solubility/dissolution and fraction absorbed (f(a)) in humans. The most accurate P(e) models for prediction of f(a) of passively transported and highly soluble compounds appear to be the 2/4/A1 rat small intestinal cell model (in-vitro and in-silico), a newly developed artificial-membrane method, and a semi-empirical approach based on in-vitro membrane affinity to immobilized lipid bilayers, effective molecular weight and physiological GI variables. The predictability of in-vitro Caco-2, in-situ perfusion and other artificial membrane methods seems comparably low. The P(e) and f(a) in humans for compounds that undergo mainly active transport were predicted poorly by all models investigated. However, the rat in-situ perfusion model appears useful for prediction of active uptake potential (complete active uptake is generally well predicted), and Caco-2 cells are useful for studying bidirectional active transport, respectively. Human intestinal in-vitro P(e), which correlates well with f(a) for passively transported compounds, could possibly also have potential to improve/enable predictions of f(a) for actively transported substances. Molecular descriptor data could give an indication of the passive absorption potential. The 'maximum absorbable dose' and 'dose number' approaches, and solubility/dissolution data obtained in aqueous media, appear to underestimate in-vivo dissolution to a considerable extent. Predictions of in-vivo dissolution should preferably be done from in-vitro dissolution data obtained using either real or validated simulated GI fluids.

Solubility and dissolution profile assessment in drug discovery

The purposes of the review are to: a) Provide a comprehensible introduction of the-state-of-the-art sciences of solubility and dissolution, b) introduce typical technologies to assess solubility and dissolution, and c) propose the best practice strategy. The theories of solubility and dissolution required in drug discovery were reviewed especially from the view point of oral absorption. The physiological conditions in the gastrointestinal fluid in humans and animals were then briefly summarized. Technologies to assess solubility and dissolution in drug discovery were then introduced. Recently, these technologies have been improved by the laboratory automation and computational technologies. Finally, the strategies to apply these technologies for a drug discovery project were discussed.

Amorphous drug nanosuspensions. 3. Particle dissolution and crystal growth

In the present paper, we have studied particle dissolution and crystal growth of the poorly water soluble drug felodipine, using fluorescence as a probe for the amount of crystalline material. Dissolution kinetics is essentially diffusion-controlled, while the rate of crystal growth is significantly slower compared to the diffusion-controlled limit. The deviation from diffusion control was characterized by the effective length, lambda, related to the kinetics of a surface integration process. Amorphous nanoparticles may be highly unstable in the presence of small amounts of crystalline particles. This is due to the fact that the molecular solubility from the amorphous nanoparticles often is at least an order of magnitude higher than the corresponding crystalline solubility. In a mixed system where crystalline nanoparticles have been added to an amorphous nanosuspension, the bulk will have a monomer concentration intermediate between the amorphous and crystalline solubilities, and is thus supersaturated with respect to the crystalline particles while being undersaturated with respect to the amorphous particles. As a consequence, the amorphous particles spontaneously dissolve, while crystalline particles grow, in a combined process which is similar to Ostwald ripening. By knowing the parameters describing dissolution and crystal growth, respectively, it was possible to simulate the outcome of controlled seeding experiments, where a small amount of crystalline nanoparticles was added to a dispersion of amorphous nanoparticles. A good agreement between model calculations and experiments was obtained including how the crystal growth rate varied with the amounts of added crystalline seeds.

A formulation comparison, using a solution and different nanosuspensions of a poorly soluble compound

The pharmacokinetic parameters of AZ68 administered as a solution have been compared with those from an amorphous and a crystalline nanosuspension using rats as in vivo specie. All formulations were administered intravenously (i.v.) and orally. The purpose of the study was to find out if the three different formulations were comparable and safe to administer. The results indicate that AZ68 is absorbed at a lower rate for crystalline nanosuspensions compared to amorphous nanosuspensions and solutions. However, the absorbed extent of the compound is similar. The results are a consequence of the lower solubility and the slower dissolution rate for crystalline material compared to amorphous substance in the gastrointestinal tract. The dissolution process is excluded for a solution, resulting in the fastest absorption rate. No significant difference was found between pharmacokinetic parameters when comparison was made between the formulations after i.v. administration. There were no adverse events observed after i.v. administration of the nanosuspensions.

Nanosizing of a drug/carrageenan complex to increase solubility and dissolution rate

In this study, we present a novel approach of nanosizing a drug/polymeric complex to increase both solubility and dissolution rate of poorly water-soluble compounds. A hydrophilic polymer, lambda-carrageenan, was first complexed with a model poorly water-soluble compound to increase the compound's aqueous solubility. The compound/carrageenan complex was further nanosized by wet-milling to enhance the dissolution rate. By complexing with carrageenan, the compound became amorphous in the complex. Using additional carrageenan as a stabilizer for nanosizing, a nanosuspension of a compound/carrageenan complex with a median particle size of about 0.3 microm was successfully developed. The particle size of the nanosuspension did not increase significantly during the lyophilization process and was stable for at least 39 days at room temperature after lyophilization. This approach of nanosizing a drug/carrageenan complex increased the aqueous solubility of the compound from less than 1 microg/mL to 39 microg/mL. In addition to increasing aqueous solubility, a nanosized compound/carrageenan complex had a faster dissolution rate than the complex, the free compound, and the nanosuspension of the free compound.

Uniform particles of pure and silica-coated cholesterol

Uniform crystalline colloidal cholesterol particles of narrow size distribution were obtained by precipitation. The method consisted of adding a miscible non-solvent (water) into cholesterol solutions of different alcohols and acetone, without any additives. The properties of the resulting particles depended in a sensitive way on the concentration of all reactants, temperature, pH, ionic strength, and aging time. The major observed effects were due to the solubility of cholesterol, which was strongly affected by the solvent mixture and temperature. Precipitation in 1-propanol/water system yielded stable dispersions of well-defined particles, which were used to evaluate the effects of different experimental parameters on their properties. Aging of stable dispersions resulted in multi-layered aggregation of the primary platelets, the degree and rate of which process was strongly affected by temperature. Finally, it was shown that the colloidal cholesterol particles could be coated with homogeneous silica layers in order to alter their surface characteristics.

Formulation-dependent toxicokinetics explains differences in the GI absorption, bioavailability and acute neurotoxicity of deltamethrin in rats

The acute neurotoxicity of pyrethroid insecticides varies markedly with the dosage vehicle employed. The objective of the present study was to assess the influence of two common vehicles on the bioavailability and toxicokinetics (TK) of a representative pyrethroid insecticide, deltamethrin (DLM), to determine whether the vehicles influence toxic potency by modifying the chemical's TK. Adult, male Sprague-Dawley rats were administered DLM iv or po, either by dissolving it in glycerol formal (GF) or by suspending it in Alkamuls (AL). Groups of rats received 10mg DLM/kg by gavage in each vehicle, as well as 2 mg/kg in GF or 10mg/kg in AL by iv injection. Serial blood samples were collected over 96 h and analyzed for their DLM content by HPLC. In a second experiment, plasma, brain, fat, liver and lung DLM concentrations were measured 2h after giving 10mg DLM/kg orally in GF or AL. In a third experiment rats received 2 or 10mg DLM/kg iv in AL or 2mg DLM/kg iv in GF. Lung DLM content was determined 15 min post injection. DLM particle size in both formulations was measured under a phase contrast microscope. DLM appeared to be completely dissolved in GF, while particle size ranged from <5 to >50 microm in AL. The bioavailability of DLM in the aqueous AL suspension was approximately 9-fold lower than in GF (1.7% versus 15%). Blood C(max) (0.95+/-0.27 versus 0.09+/-0.01 microg/ml) and AUC(0)(48h) (5.49+/-0.22 versus 0.61+/-0.14 microg.h/ml) were markedly higher in the GF gavage group. Tissue DLM levels were also significantly higher in the GF animals at 2h. The 10mg/kg po and 2mg/kg iv doses of DLM in GF produced moderate salivation and slight tremors. Rats receiving the insecticide in AL were asymptomatic. IV injection of the AL suspension resulted in trapping of much of the dose in the pulmonary capillaries. As anticipated, the injected suspension had a longer half-life and slower clearance than did the GF formulation. In summary, limited dissolution of the highly lipophilic DLM particles in the AL suspension severely limited DLM's GI absorption, bioavailability, target organ deposition and acute neurotoxic potency.

Solid-phase peptide synthesis using nanoparticulate amino acids in water

Solid-phase peptide synthesis has many advantages compared with solution peptide synthesis. However, this procedure requires a large amount of organic solvents. Since safe organic solvent waste disposal is an important environmental problem, a technology based on coupling reaction of suspended nanoparticle reactants in water was studied. Fmoc-amino acids are used widely, but most of them show low solubility in water. We prepared well-dispersible Fmoc-amino acid nanoparticles in water by pulverization using a planetary ball mill in the presence of poly(ethylene glycol). Leu-enkephalin amide was prepared successfully using the nanoparticulate Fmoc-amino acid on a poly(ethylene glycol)-grafted Rink amide resin in water.

In vitro and in vivo suppression of hepatocellular carcinoma growth by chitosan nanoparticles

Chitosan nanoparticles (CNP), a kind of widely used drug carrier, have shown potent cytotoxic effects on various tumour cell lines in vitro and in vivo. This study sought to evaluate the antitumour effect of CNP on growth of human hepatocellular carcinoma (BEL7402) and the possible mechanisms involved. Cells were grown in the absence and presence of various concentrations of CNP with mean particle size of about 40nm. Cell viability, ultrastructural changes, surface charge, mitochondrial membrane potential, reactive oxygen species (ROS) generation, lipid peroxidation, DNA fragmentation and fatty acid composition were analysed by MTT assay, electron microscopy, zetasizer analysis, flow cytometry, spectrophotometric thiobarbituric (TBA) assays, DNA agarose gel electrophoresis and GC/MS respectively. For in vivo experiments, male BABL/c nude mice were implanted with BEL7402 cells subcutaneously to establish human hepatoma model. Chitosan, saline, and CNP with different mean particle size (40, 70 and 100nm) were administrated by oral administration (1mg/kg body weight). Tumour and body weight were measured, morphologic changes of tumour and liver tissues were studied under electron microscope. In vitro, CNP exhibited high antitumour activities with an IC(50) value of 15.01microg/ml, 6.19microg/ml and 0.94microg/ml after treatment for 24h, 48h and 72h respectively. CNP could induce cell necrosis observed by electron microscope and DNA fragmentation. The antitumour mechanism was mediated by neutralisation of cell surface charge, decrease of mitochondrial membrane potential and induction of lipid peroxidation. The tumour growth inhibitory rates on BEL7402 cells in nude mice treated with chitosan and CNP with different mean particle size (40, 70 and 100nm) were 24.07%, 61.69%, 58.98% and 34.91% respectively. Typical necrotic morphological changes of tumour tissues and no liver abnormalities were found under electron microscope. In this paper, results show a strong antitumour effect of CNP on human hepatoma cell line BEL7402 in vitro and in vivo. These findings suggest that CNP could be a kind of promising agent for further evaluations in the treatment of hepatocellular carcinoma.

The road map to oral bioavailability: an industrial perspective

Optimisation of oral bioavailability is a continuing challenge for the pharmaceutical and biotechnology industries. The number of potential drug candidates requiring in vivo evaluation has significantly increased with the advent of combinatorial chemistry. In addition, drug discovery programmes are increasingly forced into more lipophilic and lower solubility chemical space. To aid in the use of in vitro and in silico tools as well as reduce the number of in vivo studies required, a team-based discussion tool is proposed that provides a 'road map' to guide the selection of profiling assays that should be considered when optimising oral bioavailability. This road map divides the factors that contribute to poor oral bioavailability into two interrelated categories: absorption and metabolism. This road map provides an interface for cross discipline discussions and a systematic approach to the experimentation that drives the drug discovery process towards a common goal - acceptable oral bioavailability using minimal resources in an acceptable time frame.

The performance of nanocarriers for transmucosal drug delivery

Most of the newly designed drug molecules are characterised by low solubility in aqueous medium, low permeability through biological membranes and/or an insufficient stability in the biological environment. Fundamental studies have provided proof-of-concept of the potential of particulate nanocarriers for overcoming these unsuitable properties. For example, it is known that polymeric nanosystems may enhance transmucosal transport of drugs with poor penetration capacities while preserving their biological activity. Moreover, in recent years it has become clear that through an appropriate selection of the nanosystem components it is possible to enhance its affinity for the mucosa and, hence, the residence time of the drug in contact with the absorptive epithelium. These properties, combined with a suitably tailored release profile can markedly increase the efficacy of pharmaceuticals. Overall, the properties that have been identified as critical for the performance of these delivery systems are particle size, surface charge and surface chemical composition. These properties are known to affect the physical and chemical stability of the nanoparticles in the biological environment as well as their ability to interact (unspecific bioadhesion, receptor-mediated interaction and so on) and, eventually, overcome biological barriers. The present article aims to critically review the latest advances in this area and to provide some insights into these complex issues. Thus, herein the most widely investigated transmucosal drug delivery nanosystems and their most promising applications are reported.

In vivo antitumor activity of chitosan nanoparticles

Chitosan nanoparticles have been synthesized as potential anticancer agents, and evaluated, in vitro, against various cancer cell lines. In this study, in vivo antitumor activity of chitosan nanoparticles against Sarcoma-180 and mouse hepatoma H22 was investigated. Chitosan nanoparticles showed significant antitumor activity in vivo. The doses and particle size made a great effect on their efficacy.

Evaluation of the in vitro activity and in vivo bioavailability of realgar nanoparticles prepared by cryo-grinding

Arsenic trioxide (As2O3) has been a research focus because of its promising anticancer effects especially in the treatment of leukemia. Another arsenic compound, realgar (As2S2), has long been used as a therapeutic agent to treat some diseases in ancient China and Europe, and its medicinal effects have attracted increasing attentions in recent years. However, its poor water-solubility unfortunately results in poor bioavailability and hampers it from being studied and used for possible clinical application. In this study, nanosized realgar particles were prepared by cryo-grinding with polyvinylpyrrolidone (PVP) and/or sodium dodecyl sulfate (SDS). Major physical properties of the respective nanosized realgar particles were characterized. Co-grinding realgar with PVP and/or SDS produced smaller and more monodisperse suspension of nanoparticles. The in vitro cytotoxic effects of such nanosized realgar particles on selected human ovarian (CI80-13S, OVCAR, OVCAR-3) and cervical (HeLa) cancer cell lines were investigated. Significant anti-proliferation effect of these realgar nanoparticles on these cancer cell lines was observed. CI80-13S was most sensitive to the nanosized realgar particles with IC50 values of less than 1 microM as As2S2, whereas the other cancer cell lines had IC50 values in a range of 2-4 microM as As2S2. The cytotoxic activity of the realgar nanoparticles to these human gynecological cell lines was comparable to arsenic trioxide observed previously. In these cancer cell lines, the cytotoxic effects were caused by apoptosis as confirmed by cell cycle and DNA laddering analysis. In in vivo study, a remarkable increase in urinary recovery of arsenic was observed in rats after a single oral administration of the cryo-ground realgar particle suspension. Ranging from 58.5 to 69.6% of the administered dose of arsenic was recovered in urine in the first 48 h from the PVP and/or SDS co-ground preparations; whereas the original realgar powder gave a urinary recovery of only 24.9%. The finding suggested that size reduction of realgar particles to nano levels could enhance its bioavailability substantially.

Critical freezing rate in freeze drying nanocrystal dispersions

Recent advances in nanoparticle technologies have significantly enhanced the oral and parenteral delivery of poorly water-soluble active pharmaceutical ingredients (APIs). However, reports have been limited on the various drying procedures to convert a liquid nanocrystal dispersions into solid dosage forms. The solid dosage form should consist of nanocrystals that can readily reconstitute into their original size upon dissolution in water. Herein, the freeze drying process of nanocrystal dispersions was examined at varying freezing rates (speed of freezing interface). As freezing rate decreases, more particle-particle aggregation developed. A critical freezing rate, below which the dried nanocrystals cannot be re-dispersed, was identified based on the plot of the particle size of reconstituted nanocrystals versus freezing rate. Freeze drying at a freezing rate near the critical value produces dry powders of bimodal particle size distribution after re-dispersion. In addition, API concentration was found to significantly affect the critical freezing rate and therefore the re-dispersibility of dry powders. The concept of critical freezing rate is critical for the development of solid dosage forms of liquid nanocrystal dispersions.

Effect of particle size reduction on dissolution and oral absorption of a poorly water-soluble drug, cilostazol, in beagle dogs

The purpose of the present study was to investigate the effects of particle size on the dissolution and oral absorption of cilostazol. Three types of suspensions having different particle size distributions were prepared of the hammer-milled, the jet-milled cilostazol crystals and the NanoCrystal spray-dried powder of cilostazol. In vitro dissolution rate of cilostazol was significantly increased by reducing the particle size. The dissolution curves of the cilostazol suspensions were in good agreement with the simulation based on the Noyes-Whitney equation. The bioavailability of cilostazol after oral administration to dogs was increased with reducing the particle size. While positive food effect on the absorption was observed for the suspensions made of the hammer-milled and the jet-milled crystals, no significant food effect was found for the suspension made of the NanoCrystal cilostazol spray-dried powder. These results could be qualitatively predicted from the in vitro dissolution data using the bio-relevant media, FaSSIF and FeSSIF. In conclusion, the NanoCrystal technology is found to be efficient to improve the oral bioavailability of cilostazol and to avoid the food effect on the absorption.

Preparation and characterization of uniform nanosized cephradine by combination of reactive precipitation and liquid anti-solvent precipitation under high gravity environment

In this work, a novel direct method, which was combined with reactive precipitation and liquid anti-solvent precipitation under high gravity environment, had been developed to prepare nanosized cephradine with narrow particle size distribution. Compared with commercial crude cephradine, the prepared cephradine showed a significant decrease in particle size, a significant increase in the specific surface area and shorter dissolving time when used for injection. The characteristic particle size was between 200-400 nm. The specific surface area increased from 2.95 to 10.87 m2/g after micronization. When the amount of L-arginin decreased from 0.25 to 0.18 g, the mixture of nanosized cephradine and L-arginine could still dissolve in 1 min. The X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) analysis indicated that the physical characteristics and molecular states remained unchanged after the recrystallization process. This method had potential application in industrial fields because of its low cost, efficient processing and the ease of scaling-up.

Nanomedicine: current status and future prospects

Applications of nanotechnology for treatment, diagnosis, monitoring, and control of biological systems has recently been referred to as "nanomedicine" by the National Institutes of Health. Research into the rational delivery and targeting of pharmaceutical, therapeutic, and diagnostic agents is at the forefront of projects in nanomedicine. These involve the identification of precise targets (cells and receptors) related to specific clinical conditions and choice of the appropriate nanocarriers to achieve the required responses while minimizing the side effects. Mononuclear phagocytes, dendritic cells, endothelial cells, and cancers (tumor cells, as well as tumor neovasculature) are key targets. Today, nanotechnology and nanoscience approaches to particle design and formulation are beginning to expand the market for many drugs and are forming the basis for a highly profitable niche within the industry, but some predicted benefits are hyped. This article will highlight rational approaches in design and surface engineering of nanoscale vehicles and entities for site-specific drug delivery and medical imaging after parenteral administration. Potential pitfalls or side effects associated with nanoparticles are also discussed.

Oleanolic acid nanosuspensions: preparation, in-vitro characterization and enhanced hepatoprotective effect

Oleanolic acid is a naturally derived triterpene used clinically in the treatment of hepatitis in China, but its poor solubility often leads to poor bioavailability. In the present study, oleanolic acid nanosuspensions were prepared by the nanoprecipitation method and then systematically characterized. The average particle size of the obtained nanosuspensions was 284.9 nm, with a polydispersity index of 0.216. Transmission electron microscopy and atomic force microscopy showed that the drug existed as spherical or near-spherical nanoparticles in the nanosuspensions. Differential scanning calorimetry and X-ray diffraction studies indicated that oleanolic acid was present in an amorphous state in the lyophilized nanosuspensions. At 25 degrees C, the saturation solubility of oleanolic acid was increased by about 6 times after nanoation (25.72 microg mL(-1) vs 4.37 microg mL(-1)). In the in-vitro drug release experiments, the lyophilized nanosuspensions showed a faster drug dissolution rate than that of the coarse drug powder (approx. 90% vs 15% during the first 20 min), and nearly 95% of the oleanolic acid was released by 120 min. As evidenced by the lower serum alanine aminotransferase activity and liver malondialdehyde content, pre-treatment with oleanolic acid nanosuspensions significantly enhanced the hepatoprotective effect of oleanolic acid against carbon tetrachloride-induced liver injury.

Supercritical fluid technology for enhanced drug delivery

The rapid advances in the development of formulation and delivery systems based on micron-sized and nanoscale drug particles will create significant benefits to the pharmaceutical industry. Complementary to traditional methods, supercritical fluid techniques have found many useful, and sometimes unique, applications in the production and processing of drug particles. In this article background information is provided on a variety of supercritical fluid techniques relevant to drug formulation and delivery, recent advances and novel applications are highlighted, and the successful development of a new supercritical fluid rapid expansion technique for producing exclusively nanoscale drug particles will be discussed. Challenges and opportunities for further development and future applications are also reviewed.

Preparation and characterization of nanocrystals for solubility and dissolution rate enhancement of nifedipine

Poorly water-soluble drugs such as nifedipine (NIF) (approximately 20 microg/ml) offer challenging problems in drug formulation as poor solubility is generally associated to poor dissolution characteristics and thus to poor oral bioavailability. In order to enhance these characteristics, preparation of nifedipine nanoparticles has been achieved using high pressure homogenization. The homogenization procedure has first been optimized in regard to particle size and size distribution. Nanoparticles were characterized in terms of size, morphology and redispersion characteristics following water-removal. Saturation solubility and dissolution characteristics were investigated and compared to the un-milled commercial NIF to verify the theoretical hypothesis on the benefit of increased surface area. Crystalline state evaluation before and following particle size reduction was also conducted through differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD) to denote eventual transformation to amorphous state during the homogenization process. Through this study, it has been shown that initial crystalline state is maintained following particle size reduction and that the dissolution characteristics of nifedipine nanoparticles were significantly increased in regards to the commercial product. The method being simple and easily scaled up, this approach should have a general applicability to many poorly water-soluble drug entities.

Amphiphilic amino acid copolymers as stabilizers for the preparation of nanocrystal dispersion

The recent advance of particle size engineering in nanometer ranges has widened the formulation opportunities of relatively water-insoluble drugs. However, the 'nanoformulation' suffers from a lack of systematic understanding about the requirements of polymeric stabilizers. Furthermore, the polymers that can be used for the preparation of nanocrystals are so limited that finding a proper stabilizer for a given formulation is often difficult. In this study, amino acid copolymers whose properties can systematically be tailored are developed, and their morphological and compositional effects are investigated. Copolymers containing lysine (K) as their hydrophilic segments, and phenylalanine (F) or leucine (L) as their hydrophobic segments successfully produce stable nanocrystals (200-300 nm) in water, while copolymers of K and alanine (A) could not generate nanosized particles. Not the morphology but the hydrophobicity of copolymers seems to be a critical parameter in the preparation of drug nanocrystals by wet comminution. The effective stabilization performance of copolymers requires the hydrophobic moiety content to be higher than 15 mol%. Comminution for only 5 min is long enough for nanocrystal preparation, and the crystallinity of drug is found intact after the processing.

Effect of liquid volume and food intake on the absolute bioavailability of danazol, a poorly soluble drug

The influence of liquid intake and a lipid-rich meal on the bioavailability of a lipophilic drug was investigated. Danazol was used as the model substance. In a randomized four-way crossover study eight healthy male volunteers received four different treatments with danazol at 2-week intervals following an overnight fast (one I.V. infusion and three oral treatments). The I.V. formulation contained 50mg danazol solubilized in 40% hydroxypropyl-beta-cyclodextrin. The oral treatments were a Standard treatment, a Standard + 800 ml water treatment and a Standard + lipid-rich meal treatment. The Standard oral treatment consisted of 200 ml water and one capsule containing 100mg danazol, three 500 mg paracetamol tablets and two 500 mg sulfasalazine tablets. Paracetamol and sulfasalazine were used as markers for gastric emptying and small intestinal transit times. Intake of danazol with a lipid-rich meal or extra 800 ml water increased the bioavailability by 400 and 55%, respectively. Gastric emptying times increased in the following order: Standard<Standard + 800 ml water<Standard + lipid-rich meal. The effects of food and liquid on danazol bioavailability can at least partly be explained by a delay in the gastric emptying time.

Nanoparticle Engineering Processes for Enhancing the Dissolution Rates of Poorly Water Soluble Drugs

Poor water solubility is an industry wide issue, especially for pharmaceutical scientists in drug discovery and drug development. In recent years, nanoparticle engineering processes have become promising approaches for the enhancement of dissolution rates of poorly water soluble drugs. Nanoparticle engineering enables manufacturing of poorly water soluble drugs into nanoparticles alone, or incorporation with a combination of pharmaceutical excipients. The use of these processes has dramatically improved in vitro dissolution rates and in vivo bioavailabilities of many poorly water soluble drugs. This review highlights several commercially or potentially commercially available nanoparticle engineering processes recently reported in the literature for increasing the dissolution properties of poorly water soluble drugs.

Nanosuspensions: a promising drug delivery strategy

Nanosuspensions have emerged as a promising strategy for the efficient delivery of hydrophobic drugs because of their versatile features and unique advantages. Techniques such as media milling and high-pressure homogenization have been used commercially for producing nanosuspensions. Recently, the engineering of nanosuspensions employing emulsions and microemulsions as templates has been addressed in the literature. The unique features of nanosuspensions have enabled their use in various dosage forms, including specialized delivery systems such as mucoadhesive hydrogels. Rapid strides have been made in the delivery of nanosuspensions by parenteral, peroral, ocular and pulmonary routes. Currently, efforts are being directed to extending their applications in site-specific drug delivery.

The role of biopharmaceutics in the development of a clinical nanoparticle formulation of MK-0869: a Beagle dog model predicts improved bioavailability and diminished food effect on absorption in human

MK-0869 (aprepitant), a potent substance P antagonist, is the active ingredient of EMEND which has recently been approved by the FDA for the prevention of chemotherapy-induced nausea and vomiting. Early clinical tablet formulations of MK-0869 showed significant food effects on absorption, suggesting that formulation could have a significant role in improving bioavailability. A Beagle dog model was developed in an effort to guide novel formulation development. Using the suspension of the micronized bulk drug used for the tablet formulations, the food effect on absorption was confirmed in the dog at a similar magnitude to that observed in humans. Further dog studies demonstrated a clear correlation between particle size and in vivo exposures, with the nanoparticle (NanoCrystal) colloidal dispersion formulation providing the highest exposure, suggesting dissolution-limited absorption. The NanoCrystal dispersion also eliminated the food effect on oral absorption in the dog at a dose of 2mg/kg. Regional absorption studies using triport dogs indicated that the absorption of MK-0869 was limited to the upper gastrointestinal tract. These results provided strong evidence that the large increase in surface areas of the drug nanoparticles could overcome the narrow absorption window and lead to rapid in vivo dissolution, fast absorption, and increased bioavailability. In addition, the dog model was used for optimizing formulation processes in which the nanoparticles were incorporated into solid dosage forms, and for selecting excipients to effectively re-disperse the nanoparticles from the dosage units. The human pharmacokinetic data using the nanoparticle formulation showed excellent correlations with those generated in the dog.

Challenges and solutions for the delivery of biotech drugs – a review of drug nanocrystal technology and lipid nanoparticles

Biotechnology allows tailor-made production of biopharmaceuticals and biotechnological drugs; however, many of them require special formulation technologies to overcome drug-associated problems. Such potential challenges to solve are: poor solubility, limited chemical stability in vitro and in vivo after administration (i.e. short half-life), poor bioavailability and potentially strong side effects requiring drug enrichment at the site of action (targeting). This review describes the use of nanoparticulate carriers, developed in our research group, as one solution to overcome such delivery problems, i.e. drug nanocrystals, solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC) and lipid-drug conjugate (LDC) nanoparticles, examples of drugs are given. As a recently developed targeting principle, the concept of differential protein adsorption is described (PathFinder Technology) using as example delivery to the brain.

Nanosuspensions in drug delivery

A surprisingly large proportion of new drug candidates emerging from drug discovery programmes are water insoluble, and therefore poorly bioavailable, leading to abandoned development efforts. These so-called 'brickdust' candidates can now be rescued by formulating them into crystalline nanosuspensions. In the process of overcoming issues involving solubility, additional pharmacokinetic benefits of the drugs so formulated have come to be appreciated. As such, insolubility issues of the past have provoked a paradigm change, which now offers novel solutions for innovative drugs of the future.

Stable Amorphous Danazol Nanostructured Powders with Rapid Dissolution Rates Produced by Spray Freezing into Liquid

The objective of this study was to produce, by spray freezing into liquid (SFL) technology, high-potency, high glass transition temperature (Tg) danazol/polymer powders that remain amorphous and exhibit high dissolution rates after 6 months. Three polymers were investigated, including polyvinylpyrrolidone (PVP) K-15, poloxamer 407, and PEG 8000. The physicochemical properties of SFL powders were characterized by X-ray diffraction (XRD), scanning electron microscopy, particle size distribution, surface area analysis, moisture content, and dissolution rate. The influence of moisture content, drug potency, and excipient type on Tg of SFL powders was investigated using modulated differential scanning calorimetry (mDSC). XRD results indicated that danazol was amorphous for each added excipient. The surface area of danazol/PVP K-15 powders (89.8 m2/g) was higher than that of danazol/PEG 8000 (12.0 m2/g) and danazol/poloxamer 407 (5.49 m2/g). The SFL powders with the various excipient types exhibited similar and significantly enhanced dissolution rates relative to micronized bulk danazol. As the potency of danazol in the SFL danazol/PVP K-15 powders was increased from 33% to 91%, the Tg decreased from 126 degrees C to 104 degrees C. The SFL powders, which were packaged in sealed 30-mL glass vials with a desiccant, were physically stable when stored at 25 degrees C for 6 months, based on dissolution rates and mDSC and XRD measurements. SFL danazol/PVP K-15 powders with high surface areas and high glass transition temperatures remain amorphous and exhibit rapid dissolution rates after 6 months' storage.

Rapid Dissolution of High‐Potency Danazol Particles Produced by Evaporative Precipitation into Aqueous Solution

High-potency danazol particles with high dissolution rates were produced by evaporative precipitation into aqueous solution (EPAS). Aqueous suspensions formed by EPAS were centrifuged to remove the nonadsorbed surfactant. The resulting surfactant-coated drug particles had extremely high drug-to-surfactant ratios greater than 5, corresponding to potencies (wt drug/wt drug + wt surfactant) as high as 93%. The mechanism of the high dissolution rates was characterized as a function of surfactant adsorption, particle size and surface area, drug crystallinity, and the contact angle for water on the drug surface. For danazol stabilized by polyvinyl pyrrolidone (PVP) alone or with sodium lauryl sulfate (SLS), small particle diameter and high surface area led to high dissolution rates with approximately 90% drug dissolved in 2 min. The crystallinity of the danazol was typically 80%. The properties of the particles and the dissolution rates were mostly unchanged under a 2-week thermal cycling stress test.

Rapid dissolving high potency danazol powders produced by spray freezing into liquid process

The objective of this study was to investigate the use of organic solvents in the spray freezing into liquid (SFL) particle engineering process to make rapid dissolving high potency danazol powders and to examine their particle size, surface area and dissolution rate. The maximum drug potency produced was 91% for SFL micronized danazol/PVP K-15. XRD indicated that danazol in the high potency SFL powders was amorphous. SEM micrographs revealed that the SFL danazol/PVP K-15 nanostructured aggregates had a porous morphology and were composed of many smooth primary nanoparticles with a diameter of about 100 nm. Surface areas of SFL danazol/PVP K-15 high potency powders were in the range of 28-115 m2/g. The SFL powders exhibited significantly enhanced dissolution rates. The rate of dissolution of micronized bulk danazol was slow; only 30% of the danazol was dissolved in 2 min. However, 95% of danazol was dissolved in only 2 min for the SFL high potency powders. The SFL process offers a highly effective approach to produce high potency danazol nanoparticles contained in larger structured aggregates with rapid dissolution rates, and is especially applicable to delivery systems containing poorly water soluble drugs.

Drug nano- and microparticles processed into solid dosage forms: physical properties

The use of nanoparticles of relatively insoluble drugs has enormously widened the window of achievable pharmacokinetic performance. For the successful development of this technology, it is essential to understand the characteristics of nanoparticles. In this study, the processability and solid dosage performance of nanoparticulates are compared with those of microparticulates. Nanoparticle suspensions are first prepared by wet comminution in the presence of stabilizers. Spray drying converts them into dried particles from which compacts are prepared. Nanoparticles easily form aggregates during spray drying. These aggregates can be slowly redispersed into nanoparticles in water. Compacts show differences in their internal structure and micromechanical deformations, according to the size of their primary particles. Stress to break and indentation hardness are found to be only slightly higher in nanoparticulate systems.

SolEmuls-novel technology for the formulation of i.v. emulsions with poorly soluble drugs

Intravenously injectable o/w emulsions of drugs being poorly soluble in water and simultaneously in oils need to be produced by locating the drug in the interfacial lecithin layer, e.g. amphotericin B. For achieving this, up to now organic solvents were required. The objective was to develop a solvent-free production method for such emulsions. Drug and the pre-formed parenteral emulsion Lipofundin were mixed and subjected to high pressure homogenisation. Drug powder and emulsions were characterised regarding size and physical stability by photon correlation spectroscopy (PCS), laser diffractometry (LD) and zeta potential measurements. Drug incorporation was studied using light microscopy, electron microscopy (EM) and a centrifugation test to separate non-dissolved drug. Amphotericin B and carbamazepine were used as model drugs. The high streaming velocities lead to accelerated drug dissolution and partitioning into the interfacial layer (so-called "solubilisation by emulsification", SolEmuls Technology). The interfacial layer could incorporate (solubilise) a certain amount of drug, revealed by EM pictures. Exceeding this concentration, hybrid dispersions were formed consisting of drug-loaded oil droplets and drug nanocrystals of similar size (approximately 200 nm). Both dispersion types are i.v. injectable opening the opportunity to deliver the drug in a concentrated form at desired low injection volume, e.g. 10 mg/ml.