A new approach for targeting to Cryptosporidium parvum using mucoadhesive nanosuspensions: research and applications

A new strategy to deliver antibiotics to the Cryptosporidium-infected gastrointestinal tract is presented. In an effort to augment the anticryptosporidial effect of clinically used drugs, mucoadhesive nanosuspensions were prepared. They have the ability to reside in the gastrointestinal tract for an extended period. The hydrogel contained bupravaquone nanosuspensions and an adhesive polymer (chitosan) powder dispersed in water. By the development of mucoadhesive nanosuspensions, a potential drug delivery system for poorly soluble drugs has been investigated to overcome bioavailability problems caused by the pathophysiological diarrhoeic situation in patients suffering from cryptosporidiosis. Adapting drug delivery systems to the situation of Cryptosporidium parvum infections in man allows increased retention times with a prolonged action at reduced elimination in the gastrointestinal tract. In this communication, in vivo data are presented to document the efficiency of bupravaquone formulated as mucoadhesive polymers to improve its activity against C. parvum.     

Evaluation of controlled-release polar lipid microparticles

The poorly soluble drug buparvaquone is used in experimental clinics against the gastrointestinal persisting parasite Cryptosporidium parvum. It was produced as nanosuspension by high pressure homogenisation. Main advantages of nanosuspensions (amongst others) are their increase of saturation solubility and dissolution velocity, improving the bioavailability of drugs. The buparvaquone nanosuspension had a bulk population of about 600 nm (analysed by photon correlation spectroscopy (PCS)). The additional analysis performed with laser diffraction showed that only a very small content of microparticles occurred, which is, for the special features of nanosuspensions, negligible because they were still below 3 microm. Another feature of nanosuspensions is the adhesion properties to surfaces, e.g. mucosa. To further increase the adhesion time of the buparvaquone nanosuspension to C. parvum, the nanosuspension was formulated with hydrogels made from mucoadhesive polymers, e.g. different types of Carbopol and chitosan. Only a small increase of the particle size of the bulk population occurred directly after the incorporation of buparvaquone nanosuspension into the hydrogels. The nanosuspension/hydrogel systems were physically long-term stable over a period of 6 months as indicated by the unchanged particle sizes.     

Drug nanocrystals of poorly soluble drugs produced by high pressure homogenisation.

For many new chemical entities (NCE) of very low solubility oral bioavailability enhancement by micronisation is not sufficient, the next step taken was nanonisation. The production of drug nanocrystals by bottom up techniques (precipitation) is briefly described, main focus is given on particle diminution by high pressure homogenisation. Homogenisation can be performed in water (DissoCubes) or alternatively in non-aqueous media or water-reduced media (Nanopure). There is also a combination process of precipitation followed by a second high energy step, e.g. homogenisation (NANOEDGE). The result is a suspension of drug nanocrystals in a liquid, the so-called nanosuspension. Presented are the physical background of the diminution process, effects of production parameters (power density, number of homogenisation cycles) on crystal size, clinical batch production and scaling up of the production. As an important point the transfer of the liquid nanosuspensions to patient convenient oral dosage forms such as tablets and capsules is described.     

Development of an intravenously injectable chemically stable aqueous omeprazole formulation using nanosuspension technology.

Omeprazole is a proton pump inhibitor, which is used for the treatment of peptic ulcers, reflux esophagitis and Zollinger-Ellison syndrome. It is a poorly soluble, chemically labile drug with a high degradation rate in aqueous media. The aim of this study was to show the feasibility of omeprazole stabilization using the DissoCubes technology and to find optimal production parameters for a stable, highly concentrated omeprazole nanosuspension. The high performance liquid chromatography analysis has proved the predominance of the nanosuspension produced by high pressure homogenization in comparison to an aqueous solution. Even 1 month after production no discoloration or drug loss was recognizable when the nanosuspension was produced at 0 degree C. As a result it can be stated that the production of nanosuspensions by high pressure homogenization is suitable for preventing degradation of labile drugs.     

Drug release and permeation studies of nanosuspensions based on solidified reverse micellar solutions (SRMS)

Solidified reverse micellar solutions (SRMS), i.e. mixtures of lecithin and triglycerides, offer high solubilisation capacities for different types of drugs in contrast to simple triglyceride systems [Friedrich, I., Müller-Goymann, C.C., 2003. Characterisation of SRMS and production development of SRMS-based nanosuspensions. Eur. J. Pharm. Biopharm. 56, 111-119]. Nanosuspensions based on SRMS were prepared by homogenisation close to the melting point of the SRMS matrix. In a first step the SRMS matrices of 1:1 (w/w) ratios of lecithin and triglycerides were loaded with 17beta-estradiol-hemihydrate (EST), hydrocortisone (HC) or pilocarpine base (PB), respectively, and subsequently ground in liquid nitrogen to minimise drug diffusion later on. The powder was then dispersed in a polysorbate 80 solution using high pressure homogenisation. The drug loading capacities of the nanosuspensions were very high in the case of poorly water-soluble EST (99% of total 0.1%, w/w, EST) and HC (97% of total 0.5%, w/w, HC) but not sufficient with the more hydrophilic PB (37-40% of total 1.0%, w/w, PB). These findings suggest SRMS-based nanosuspensions to be promising aqueous drug carrier systems for poorly soluble drugs like EST and HC. Furthermore, in vitro drug permeation from the different drug-loaded nanosuspensions was performed across human cornea construct (HCC) as an organotypical cell culture model. PB permeation did not differ from the nanosuspension and an aqueous solution whereas the permeation coefficients of HC-loaded nanosuspensions were reduced in comparison to aqueous and oily solutions of HC. However, the permeated amount was higher from the nanosuspensions due to a much lower HC concentration in the solution than that in the nanosuspension (solution 0.02%, w/w, versus nanosuspension 0.5%, w/w). The high drug load of the nanoparticles provides prolonged HC release. Permeated amounts of EST were reduced in comparison to HC and only detectable with an ELISA technique. The EST release from nanosuspensions and different EST-loaded systems revealed a prolonged EST release from the nanoparticulate systems in contrast to a faster release of an oily solution of an equal EST concentration. With regard to an aqueous EST suspension of similar concentration which represents a depot system the release rate from the nanosuspensions revealed the same order of magnitude which points again to a prolonged release potential of the nanosuspensions.     

Nanosuspension as an ophthalmic delivery system for certain glucocorticoid drugs

Poorly-water-soluble compounds are difficult to develop as drug products using conventional formulation techniques. The use of nanotechnology to formulate poorly-water-soluble drugs as nanosuspensions offers the opportunity to address many of the deficiencies associated with this class of molecules. In the present study, the high pressure homogenization method used to prepare nanosuspensions of three practically insoluble glucocorticoid drugs; hydrocortisone, prednisolone and dexamethasone. The effect of particle size in the micron and nano-size ranges as well as the effect of viscosity of the nanosuspension on the ocular bioavailability was studied by measuring the intraocular pressure of normotensive Albino rabbits using shiØetz tonometer. The results show that compared to solution and micro-crystalline suspensions it is a common feature of the three drugs that the nanosuspensions always enhance the rate and extent of ophthalmic drug absorption as well as the intensity of drug action. In the majority of cases nanosuspensions extend the duration of drug effect to a significant extent. The data presented confirms that nanosuspensions differ from micro-crystalline suspensions and solution as ophthalmic drug delivery systems and that the differences are statistically, highly to very highly significant. The results confirm also the importance of viscosity of nanosuspension especially in increasing the duration of drug action.     

In vitro dissolution and bioavailability study of furosemide nanosuspension prepared using design of experiment (DoE)

Background

Nanotechnology can offer the advantages of increasing solubility and bioavailability of delivering drugs like Furosemide. The aim of the current study is to investigate the in vitro and in vivo performance of furosemide nanosuspensions.

Formulation of amphotericin B as nanosuspension for oral administration

Amphotherin B was formulated in a nanosuspension as a new oral drug delivery system for the treatment of experimental visceral leishmaniasis. Amphotericin B (AmB) nanosuspensions were produced by high pressure homogenisation obtaining particles with a PCS diameter of 528 nm. Environmental stability was determined in artificial gastrointestinal fluids at different pH and electrolyte concentrations. In vivo efficacy was determined in a mouse model of visceral leishmaniasis. Following oral administration (5 mg kg(-1)), micronised amphotericin B did not show any curative effect. However, administrations of amphotericin B nanosuspension, reduced liver parasite load by 28.6% compared to untreated controls.     

Studies on pharmacokinetics and tissue distribution of oridonin nanosuspensions

The purpose of the present study was to investigate the effects of particle size on the pharmacokinetics and tissue distribution of oridonin nanosuspensions after intravenous administration. Two oridonin nanosuspensions with markedly different size were prepared by high pressure homogenization method. The particle size of nanosuspension A is 103.3+/-1.5nm, while B is 897.2+/-14.2nm. Dissolution studies showed that complete dissolution could be obtained within 10min for nanosuspension A, however, nanosuspension B showed a slower dissolution, only 85.2% dissolved by 2h. The pharmacokinetics and tissue distribution of oridonin nanosuspensions A and B were studied after intravenous administration using New Zealand rabbits and Kunming mice as experimental animals, respectively. An Oridonin control solution was studied parallelly. The results showed that oridonin nanosuspension A exhibited pharmacokinetic and biodistribution properties similar to solution due to its rapid dissolution in blood circulation. Oridonin nanosuspension B, however, showed a high uptake in RES organs, meanwhile exhibited a markedly different pharmacokinetic property compared to nanosuspension A. These differences could be attributed to the different particle size of the two nanosuspensions considering their zeta potential had no significant difference. In conclusion, particle size showed obvious effects on pharmacokinetics and tissue distribution of nanosuspensions.     

Preparation and evaluation of nanosuspensions for enhancing the dissolution of poorly soluble drugs

Poorly water-soluble compounds are difficult to develop as drug products using conventional formulation techniques and are frequently abandoned early in discovery. In the present study, the melt emulsification method traditionally used to prepare solid lipid nanoparticles was adapted to produce drug nanosuspensions. The method was evaluated in comparison with the well known solvent diffusion process for ibuprofen as a model drug. Control of the preparation variables (stabilizers, drug content, homogenization procedure and cooling conditions) allowed formation of nanosuspensions with diameters less than 100 nm. The major advantage of the melt emulsification method over the solvent diffusion method is the avoidance of organic solvents during production, although the mean particle size is slightly greater. The combination of Tween 80 and PVP K25 as stabilizers yields nanosuspensions with the smallest average particle size. The formulation of ibuprofen as a nanosuspension, either in the form of lyophilized powder or granules, was very successful in enhancing dissolution rate, more than 65% of the drug being dissolved in the first 10 min compared to less than 15% of the micronized drug. The increase in in vitro dissolution rate may favourably affect bioavailability and improve safety for the patient by decreasing gastric irritancy.     

Top-down production of drug nanocrystals: nanosuspension stabilization, miniaturization and transformation into solid products

During the last 10-15 years, the formulation of drugs as nanocrystals has rapidly evolved into a mature drug delivery strategy, with currently five products on the market. The major characteristic of these systems is the rapid dissolution velocity, enabling bioavailability enhancement after oral administration. This mini-review focuses on recent advances with respect to three topics considering drug nanocrystals. The first topic is nanosuspension stabilization. A current literature status is provided and special attention is given to studies attempting to extend our physicochemical understanding of the underlying principles. The second part describes recent advances on miniaturization of nanosuspension production, to enable formulation screening during preclinical development. Finally, literature available on further nanosuspensions solidification is discussed, focussing on the maintenance of the preservation of the rapid dissolution properties of the nanocrystals after further downstream processing.     

Pharmacokinetic evaluation of oral fenofibrate nanosuspensions and SLN in comparison to conventional suspensions of micronized drug

An increasing number of newly developed drugs show bioavailability problems due to poor water solubility. Formulating the drugs as nanosuspensions may help to overcome these problems by increasing saturation solubility and dissolution velocity. In the present study the bioavailability of the poorly soluble fenofibrate following oral administration was investigated in rats. Four formulations were tested: a nanosuspension type DissoCube(R), one solid lipid nanoparticle (SLN) preparation and two suspensions of micronized fenofibrate as reference formulations, one suspension in sirupus simplex and a second in a solution of hydroxyethy-cellulose in physiological saline. Both colloidal drug delivery systems showed approximately two-fold bioavailability enhancements in terms of rate and extent compared to the reference formulations. No significant differences were found in AUC(0-22 h) as well as in C(max) and t(max) between the two colloidal delivery systems. In conclusion, nanosuspensions may be a suitable delivery system to improve the bioavailability of drugs with low water solubility.     

Nanosuspensions for the formulation of poorly soluble drugs: I. Preparation by a size-reduction technique

A basic problem of poorly soluble drugs is often an insufficient bioavailability. To allow the i.v. injection of these drugs, they were formulated as nanosuspensions by high pressure homogenization. The effect of the production parameters pressure and cycle number on the mean particle size and on the polydispersity of the nanosuspension was investigated with special attention to contamination by microparticles — the limiting factor for i.v. injection. Properties of the nanosuspensions are increased saturation solubility C_s and dissolution rate dc/dt. These phenomena are explained using the Prandtl and the Ostwald–Freundlich equations. These properties promote the dissolution of the nanosuspensions in the blood after i.v. injection. The size distribution obtained and the use of an APV Gaulin homogenizer (FDA approved for parenterals) lead to a pharmaceutical product considered acceptable by the regulatory authorities.     

Efficiency of a dexamethasone nanosuspension as an intratympanic injection for acute hearing loss

Dexamethasone sodium phosphate (Dex-SP) is the most commonly used drug administered via intratympanic injection for the treatment of acute hearing loss, but its penetration efficiency into the inner ear is very low. To address this problem, we evaluated the possibility of administering dexamethasone nanosuspensions via intratympanic injection because hydrophobic drugs might be more effective in penetrating the inner ear. Three types of dexamethasone nanosuspensions were prepared; the dexamethasone nanoparticles in the three nanosuspensions were between approximately 250 and 350 nm in size. To compare the efficiency of Dex-SP and dexamethasone nanosuspension in delivering dexamethasone to the inner ear, the concentrations of dexamethasone in perilymph and cochlear tissues were compared by liquid chromatography–mass spectrometry. The dexamethasone nanosuspensions resulted in significantly higher drug concentrations in perilymph and cochlear tissues than Dex-SP at 6 h; interestingly, animals treated with nanosuspensions showed a 26-fold higher dexamethasone concentrations in their cochlear tissues than animals treated with Dex-SP. In addition, dexamethasone nanosuspension caused better glucocorticoid receptor phosphorylation than Dex-SP both in vitro and in vivo, and in the ototoxic animal model, the nanosuspension showed a significantly better hearing-protective effect against ototoxic drugs than Dex-SP. In the in vivo safety evaluation, the nanosuspension showed no toxicity at concentrations up to 20 mg/mL. In conclusion, a nanosuspension of dexamethasone was able to deliver dexamethasone to the cochlea very safely and efficiently and showed potential as a formula for intratympanic injection.     

Development and characterization of mucoadhesive nanosuspension of ciprofloxacin

Mucoadhesive nanosuspension of ciprofloxacin was designed in order to improve the solubility, bioavailability and efficacy for the treatment of typhoid fever. The identity and purity of drug was established. The compatibility of drug with various excipients was ascertained by FTIR techniques, which indicated no interaction between the drug and excipients. Four different formulations were prepared by optimizing various parameters using different polymers like soya lecithin, pluronic F68, polyvinyl alcohol, and polyvinylpyrrolidone K30. Particle size and polydispersity index were determined by photon correlation spectroscopy. Average particle size of different formulations was found to be between 503-1844 nm. The zeta potential of all formulations was found to be around +/- 20 My indicating satisfactory physical stability. Scanning electron microscopy showed that process parameters affect the crystal morphology. The promising formulations prepared from combination of soya lecithin and pluronic F68 and those based on soya lecithin alone were subjected to dissolution profile studies. The later formulation exhibited fast dissolution rate as compared to the former. Thus nanosus-pension based on soya lecithin was incorporated into hydrogels prepared using different grades of carbopol 934 and 971 as mucoadhesive polymers. After 10 h, mucoadhesive nanosuspensions showed 45-56% release. The developed mucoadhesive nanosuspensions exhibited satisfactory physical stability. The studies indicated potential of these formulations as novel gastroretentive systems.     

A screening study of surface stabilization during the production of drug nanocrystals

In order to establish a knowledge base for nanosuspension production, a screening was performed on 13 different stabilizers at 3 concentrations for 9 structurally different drug compounds. Concerning the stabilizers tested, the group of semi-synthetic polymers was the least performant (stable nanosuspensions were obtained in only 1 out of 10 cases). For the linear synthetic polymers, better results were obtained with povidones, however poly(vinyl alcohol) did not result in adequate stabilization. The synthetic copolymers showed even higher success rates, resulting in nanosuspensions in two out of three cases when applied at a 100 wt% concentration (relative to the drug weight). Finally, the surfactants gave the best results, with TPGS being successful at concentrations of 25 or 100 wt% of the drug weight for all compounds tested. From the point of view of drug compound, large differences could be observed upon evaluation of the relative number of formulations of that compound resulting in nanosuspensions. It was found that the hydrophobicity of the surfaces, as estimated by the adsorbed amount of TPGS per unit of surface area of nanosuspensions stabilized with 25 wt% TPGS, was decisive for the agglomeration tendency of the particles and hence the ease of nanosuspensions stabilization.     

吗替麦考酚酯纳米混悬剂的制备及其兔眼内生物学性质研究

目的：研究吗替麦考酚酯纳米混悬剂在兔眼角膜黏附性、泪液和房水药物动力学特性。方法：以薄膜分散．高压乳匀法制备纳米混悬剂,测定其理化性质。HPLC法检测角膜黏附、泪液和房水中的吗替麦考酚酯和麦考酚酸的含量。结果：混悬剂滴眼液呈米黄色乳液状,纳米混悬剂药物粒子呈圆球状,粒径均一,纳米混悬剂平均粒径592nm,多分散系数Pdl为0．114,Zeta电位为-29．6mV。与普通混悬剂滴眼液相比,纳米混悬剂的角膜黏附性、泪液和房水中药物浓度明显提高。结论：纳米混悬剂可以促进和提高吗替麦考酚酯眼局部给药后角膜黏附和药物吸收。     

Solution calorimetry as an alternative approach for dissolution testing of nanosuspensions

The formulation of poorly soluble drugs as nanocrystals/nanosuspensions has rapidly evolved during the past decade into a mature drug-delivery strategy. The major characteristic of these systems is the high drug dissolution rate, enabling bioavailability enhancement after oral administration. It is therefore of great importance to have access to analytical methodology that is able to accurately monitor the extreme fast dissolution process of such formulations. The aim of the present study was to evaluate solution calorimetry as a novel approach to measure the dissolution rate of nanosuspensions by recording the temperature change in the dissolution vessel during the dissolution process of the nanocrystals. The applicability was tested on different nanosuspensions made up of three model drugs: naproxen, cinnarizine and an investigational API, i.e. compound A. The dissolution process of all nanosuspensions investigated was completed within less than 1 min. During this period, sufficient data points were collected to transform temperature offset data to cumulative heat of solution pointing to the potential of this technique. However, of significant concern is the fact that this technique measures the total heat produced or consumed by all processes that occur during the dissolution, e.g. the heat of mixing when the nanosuspension comes in contact with the dissolution medium. Erroneous conclusions will result if phenomena other than dissolution are not accounted for.