Effect of lysozyme on the stability of polyester nanocapsules and nanoparticles: stabilization approaches.

The efficacy of colloidal particles as drug carriers is closely related to their interaction with proteins and enzymes in different body fluids. In the present work, we analysed the interaction phenomenon between lysozyme (LZM), a positively charged enzyme that is highly concentrated in mucosas, and two different drug carriers: nanocapsules made of an oily core coated by the polymer poly-epsilon-caprolactone (PECL) and nanoparticles made solely of PECL. Results showed that the interaction of LZM with these colloidal drug carriers is highly affected by their surface charge. Nanocapsules, because of their important negative charge (-40 mV), adsorbed a great amount of LZM, which is positively charged. This adsorption process, which was also evidenced by the significant reduction of the nanocapsules' negative surface charge, led to the degradation of the polymer coating and the aggregation of the nanocapsules. In contrast, nanoparticles had a low negative surface charge (-8 mV) and adsorbed only a small amount of LZM, which did not cause the destabilization of the system. Furthermore, the molecular weight of the polymer forming the nanoparticles did not change. Finally, it was observed that the destabilizing effects caused by the adsorption of LZM onto the nanocapsules can be prevented by previous adsorption of the cationic poly(amino acid) poly-L-lysine. Using this approach the adsorption of LZM was hindered and its consequences avoided.

Design of a new multiparticulate system for potential site-specific and controlled drug delivery to the colonic region.

A multiparticulate dosage form consisting of a hydrophobic core coated with a pH-dependent polymer is proposed for colonic specific delivery of drugs. Different approaches for colon-specific drug delivery have been studied over the last decade, including prodrugs, polymeric coating using pH-sensitive or bacterial degradable polymers and matrices. In this work, we present a new multiparticulate system to deliver active molecules to the colonic region, which combines pH-dependent and controlled drug release properties. This system was constituted by drug loaded cellulose acetate butyrate (CAB) microspheres coated by an enteric polymer (Eudragit(R) S). Both, CAB cores and pH-sensitive microcapsules, were prepared by the emulsion-solvent evaporation technique in an oily phase. Ondansetron (OS) and budesonide (BDS), two interesting drugs with a potentially new application for the local treatment of intestinal disorders, were efficiently microencapsulated in CAB microspheres at different polymer concentrations (6 and 8%). These hydrophobic cores (about 60 and 110 micrometer in size, respectively) were then microencapsulated with Eudragit(R) S, resulting in multinucleated structures, except in the case of BDS-CAB microspheres prepared at 8% CAB concentration, in which more mononucleated microcapsules were obtained. The in vitro drug release studies of pH-sensitive microcapsules containing the hydrophobic cores showed that no drug was released below pH 7. After that, CAB microspheres efficiently controlled the release of BDS, the release behavior being affected by the different polymer concentration used in their preparation. However, OS-CAB microspheres did not maintain their controlled-release properties once the enteric polymer dissolved. The extraction of the drug by the Eudragit(R) solvent during the second microencapsulation process was in this case the cause for the failure of the controlling release mechanism.

Design of microencapsulated chitosan microspheres for colonic drug delivery.

Among the different approaches to achieve colon-selective drug delivery, the use of polymers, specifically biodegraded by colonic bacteria, holds great promise. In this work a new system which combines specific biodegradability and pH-dependent release is presented. The system consists of chitosan (CS) microcores entrapped within acrylic microspheres. Sodium diclofenac (SD), used as a model drug, was efficiently entrapped within CS microcores using spray-drying and then microencapsulated into Eudragit L-100 and Eudragit S-100 using an oil-in-oil solvent evaporation method. The size of the CS microcores was small (1.8-2.9 microns) and they were encapsulated within Eudragit microspheres (size between 152 and 233 microns) forming a multireservoir system. Even though CS dissolves very fast in acidic media, at pH 7.4, SD release from CS microcores was delayed, the release rate being adjustable (50% dissolved within 30-120 min) by changing the CS molecular weight (MW) or the type of CS salt. Furthermore, by coating the CS microcores with Eudragit, perfect pH-dependent release profiles were attained. No release was observed at acidic pHs, however, when reaching the Eudragit pH solubility, a continuous release for a variable time (8-12 h) was achieved. A combined mechanism of release is proposed, which considers the dissolution of the Eudragit coating, the swelling of the CS microcores and the dissolution of SD and its further diffusion through the CS gel cores. In addition, infrared (IR) spectra revealed that there was an ionic interaction between the amine groups of CS and the carboxyl groups of Eudragit, which provided the system with a new element for controlling the release. In conclusion, this work presents new approaches for the modification of CS as well as a new system with a great potential for colonic drug delivery.

Design and evaluation of chitosan/ethylcellulose mucoadhesive bilayered devices for buccal drug delivery.

This paper describes the preparation of new buccal bilayered devices comprising a drug-containing mucoadhesive layer and a drug-free backing layer, by two different methods. Bilaminated films were produced by a casting/solvent evaporation technique and bilayered tablets were obtained by direct compression. The mucoadhesive layer was composed of a mixture of drug and chitosan, with or without an anionic crosslinking polymer (polycarbophil, sodium alginate, gellan gum), and the backing layer was made of ethylcellulose. The double-layered structure design was expected to provide drug delivery in a unidirectional fashion to the mucosa and avoid loss of drug due to wash-out with saliva. Using nifedipine and propranolol hydrochloride as slightly and highly water-soluble model drugs, respectively, it was demonstrated that these new devices show promising potential for use in controlled delivery of drugs to the oral cavity. The uncrosslinked chitosan-containing devices absorbed a large quantity of water, gelled and then eroded, allowing drug release. The bilaminated films showed a sustained drug release in a phosphate buffer (pH 6.4). Furthermore, tablets that displayed controlled swelling and drug release and adequate adhesivity were produced by in situ crosslinking the chitosan with polycarbophil.

Development of new chitosan-cellulose multicore microparticles for controlled drug delivery.

Chitosan (CS) is a very interesting biomaterial for drug delivery; however its use in oral administration is restricted by its fast dissolution in the stomach and limited capacity for controlling the release of drugs. To address this limitation, a new microparticulate CS controlled release system, consisting of hydrophilic CS microcores entrapped in a hydrophobic cellulosic polymer, such as cellulose acetate butyrate (CAB) or ethyl cellulose (EC) was proposed. These microparticles were obtained with different types of CS and various core/coat ratios, with the particle size in all cases being smaller that 70 microns. Using sodium diclofenac (SD) and fluorescein isothiocyanate-labeled bovine serum albumin (FITC-BSA) as model compounds, the properties of these new microparticles for the entrapment and controlled release of drugs and proteins were investigated. Results showed that the entrapment efficiency of SD was very high irrespective of the processing conditions. Furthermore, for both model compounds (SD and FITC-BSA) it was possible to modulate the in vitro release of the encapsulated molecules by changing the core properties (CS salt, Mw, core/coat ratio) or the coating polymer. The microparticles were stable at low pH and thus, suitable for oral delivery without requiring any harmful cross-linkage treatment.

Comparative in vitro evaluation of several colloidal systems, nanoparticles, nanocapsules, and nanoemulsions, as ocular drug carriers.

Three different colloidal carriers, namely, nanoparticles and nanocapsules made of poly-epsilon-caprolactone and submicron emulsions, were designed, and their capacity for increasing the comeal penetration of drugs was investigated. The three systems differed in their inner structure and composition, but they had a similar size (200-250 nm) and a negative superficial charge (-16 to -42 mV). Indomethacin, which was used as a model drug, was dispersed at a molecular level within the colloidal systems, no chemical interaction between the polymer and the drug being detected. Release of the encapsulated indomethacin occurred very rapidly upon high dilution in a buffered medium and was independent of the composition of the system. The in vitro comeal penetration of the encapsulated indomethacin was more than 3-fold that of the commercial eye drops. This increased penetration was similar for the three formulations investigated, which therefore excludes the influence of the inner structure or chemical composition of the colloidal systems on the comeal penetration of indomethacin. Thus, it could be stated that the main factor responsible for the favorable comeal transport of indomethacin is the colloidal nature of these carriers rather than their inner structure or composition.

Surface pressure-area isotherms of mixed cyclosporin-poly(isobutylcyanoacrylate) monolayers spread at the air/water interface.

The pi-A isotherms of mixed monolayers of cyclosporin and poly(isobutylcyanoacrylate) (PIBCA) show that the molecular areas of cyclosporin and PIBCA are additive regardless of the pH of the substrate or the physical state of the monolayers. All these mixed films collapse at the same surface pressure; therefore, application of the two-dimensional phase rule implies that cyclosporin and PIBCA are immiscible at the interface. This conclusion may have important implications with regard to the formulation of PIBCA-cyclosporin nanoparticles for cyclosporin administration, though further research in this direction will require consideration of the role played by the coadjuvants used for PIBCA polymerization during nanoparticle formation.

Utility of nuclear magnetic resonance spectroscopy to characterize the structure of dexamethasone sodium phosphate inclusion complexes with cyclodextrins in solution and to analyze potential competitive effects.

The interaction between dexamethasone sodium phosphate (DSP) and four cyclodextrin (CyD) derivatives [2,6-di-O-beta-cyclodextrin (DIMEB), gamma-cyclodextrin (gamma-CyD), and hydroxypropyl-beta-cyclodextrin with either 2.7 or 4.6 degrees of substitution (HPbetaCyD 2.7 and HPbetaCyD 4.6, respectively)] was investigated by proton nuclear magnetic resonance spectroscopy (1H NMR). The data suggested the formation of inclusion complexes in solution in which B and C rings of the molecule are located inside the cavity. Nevertheless, the structure, in terms of depth within CyD, depends on the derivative considered. Molecular mechanics calculations of DSP complexes with DIMEB and gamma-CyD support the NMR results. The potential displacement of DSP from the CyD cavity by usual ophthalmic drugs (e.g., polymyxin B, trimethoprim, and benzalkonium chloride) was determined by NMR. The technique has been found useful to analyze this problem in pharmaceutical preparations.

Complexation of the interferon inducer, bropirimine, with hydroxypropyl-beta-cyclodextrin.

Bropirimine (ABPP) is an orally active immunomodulator that increases endogenous alpha-interferon and other cytokines used clinically against carcinoma in situ of the bladder. The oral absorption of ABPP is poor because its low solubility in water. The purpose of this study is to develop a technological procedure useful to increase the water solubility of ABPP. To this end, the interaction of ABPP with several cyclodextrin derivatives-alpha-, beta-, gamma- and hydroxypropyl-beta-cyclodextrin with a degree of substitution 2.7 (HPbetaCD) was studied and the effect of the complexation process on the water solubility of the drug was evaluated. The best results were obtained with the hydroxypropyl derivative, HPbetaCD, that interacts in a 1:1 drug:cyclodextrin molar ratio. The inclusion complex ABPP-HPbetaCD was characterized in solution by nuclear magnetic resonance (1H-NMR). The solid inclusion complex was obtained by freeze-drying and characterized by differential scanning calorimetry (DSC), X-ray diffractometry and mass spectrometry. The dissolution rate of ABPP from the HPbetaCD solid inclusion complex was increased compared to the powdered drug but not differences were found between the complex and a physical mixture with a similar molar ratio. The increase of the dissolution rate of the drug can be attributed to the breakdown in solution of the drug dimers in the presence of the cyclodextrin and to the complex formation.

Controlled-release liquid suspensions based on ion-exchange particles entrapped within acrylic microcapsules.

Eudragit RS/RL polymers were used to prepare microcapsules containing terbutaline-loaded ion-exchange resins, with the final aim of formulating this anti-asthmatic drug in a controlled-release liquid form. Oil-in-oil (o/o) and oil-in-water (o/w) solvent evaporation procedures were conveniently modified in order to encapsulate the resin cores. The microcapsules were then suspended in a hydroxypropylmethylcellulose solution of adequate viscosity and palatability, and stored at 20 degrees C and ambient humidity conditions for a 6-month period. Stability studies of the dispersed microparticles were performed in order to evaluate the changes occurred in the diffusion of the drug to the suspending medium and in the dissolution behaviour during storage. The morphological alterations of the stored microcapsules were followed throughout the duration of the study by scanning electron microscopy. The polymer coatings of microcapsules prepared by the o/o method broke up on the first day of storage, while those made by the aqueous procedure remained intact during all the storage period. This agreed with the modification observed in the controlled-release profiles of terbutaline in the case of microcapsules prepared by the o/o method, which completely changed after the first week of storage. On the contrary, the microcapsules prepared by the aqueous method showed identical controlled-release profiles for all the stability study. The different behaviour of both types of microcapsules was attributed to the swelling suffered by the resin particles in contact with the aqueous suspending medium, which was higher in the microcapsules prepared by the o/o technique. In fact, in the anhydrous procedure, the microencapsulation was carried out on the shrunken resin particles, whereas in the o/w method, the presence of water during the microencapsulation process allowed the coating of the swollen particles, thus avoiding the further problem of rupture of the polymer coating.

The effect of the molecular weight of polyethylene glycol on the bioavailability of paracetamol-polyethylene glycol solid dispersions.

A controlled study of the bioavailability of paracetamol in solid dispersion with PEG 6000, 10000 and 20000 has been made. The total amount of paracetamol excreted in urine increased with molecular weight of the PEG, but the rate of absorption of the drug was unaffected.

Improvement of ocular penetration of amikacin sulphate by association to poly(butylcyanoacrylate) nanoparticles.

The main objective of this paper was to investigate the ability of polycyanoacrylate nanoparticles to improve the corneal penetration of hydrophilic drugs. Three different nanoparticle formulations were prepared by changing the nature of the stabilizer agent (Dextran 70000, Synperonic F 68 and sodium lauryl sulphate). The significant influence of the stabilizer type on the particle size, electrophoretic mobility and on the drug loading efficiency was proved. Moreover, the ocular disposition of amikacin was affected by its association to nanoparticles, displaying the most interesting results when Dextran 70000 was employed for preparation of nanoparticles. The increase of the amikacin concentration in cornea and aqueous humour was statistically significant for this nanoparticle formulation with respect to the other formulations and the control solution. The in-vitro release profiles obtained using a dialysis system were similar for all the nanoparticle formulations and for the control solution, indicating that drug molecules are desorbed from the nanoparticles quickly enough to maintain the equilibrium concentration in the dialysis system.

Improved ocular bioavailability of indomethacin by novel ocular drug carriers.

The ability of different drug carriers to improve the ocular bioavailability of drugs was investigated in the rabbit eye. The assayed drug carriers were suspensions of nanoparticles, nanocapsules and microparticles made of poly-epsilon-caprolactone (PECL) and a submicron emulsion. Results indicated that the three submicron systems, nanoparticles, nanocapsules and emulsion, increased more than 3-fold the indomethacin concentration in the cornea, aqueous humour and iris-ciliary body at 0.5 and 1 h post-instillation. Furthermore, an increased indomethacin ocular bioavailability of 300% was observed after instillation of the submicron systems in comparison with the value obtained for a commercial solution. In contrast, the microparticles hardly increased the ocular bioavailability of indomethacin. The mechanism of interaction of the colloidal carriers with the corneal epithelium was investigated by confocal laser scanning microscopy. Confocal images indicated that submicron particles penetrate into the corneal epithelium cells by an endocytic mechanism. The similar behaviour of the three colloidal carriers suggests that any of their specific ingredients (PCEL, lecithin and oil) acts as a penetration enhancer or an endocytotic stimulator. On the other hand, the favourable ocular penetration of indomethacin when encapsulated in the colloidal carriers, but not in the microparticles, led us to assume that the colloidal nature of these carriers is the main factor responsible for the increased ocular bioavailability of indomethacin. PECL nanoparticles and nanocapsules as well as submicron emulsions are shown to be novel corneal drug carriers, thus representing a useful approach for increasing the ocular bioavailability of drugs.

PEG-PLA nanoparticles as carriers for nasal vaccine delivery.

This report presents an overview of the potential of nanoparticles as nasal carriers for drug/vaccine administration. In addition, this report shows, for the first time, the efficacy of polylactic acid nanoparticles coated with a hydrophilic polyethyleneglycol coating (PEG-PLA nanoparticles) as carriers for the nasal transport of bioactive compounds. For this purpose, tetanus toxoid (TT), a high molecular weight protein (Mw 150,000 Da), was chosen as a model antigen and encapsulated in the PEG-PLA nano- and microparticles (200 nm and 1.5 microm respectively). These nanosystems were first characterized for their stability in the presence of lysozyme and also for their size, electrical charge, loading efficiency, in vitro release of antigenically active toxoid and afterwards, these formulations were administered intranasally to mice and the systemic and mucosal anti-tetanus responses were evaluated for up to 24 weeks. Additionally, PEG-PLA particles labeled with rhodamine 6G were administered intranasally to rats in order to visualize their interaction with the nasal mucosae by fluorescence microscopy. Their behavior was compared with that of the well known PLA nanoparticles (200 nm). The results showed that PLA nanoparticles suffered an immediate aggregation upon incubation with lysozyme, whereas the PEG-coated nanoparticles remained totally stable. The antibody levels elicited following i.n. administration of PEG-coated nanoparticles were significantly higher than those corresponding to PLA nanoparticles. Furthermore, PEG-PLA nanoparticles generated an increasing and a long lasting response. The qualitative fluorescence microscopy studies revealed that PEG-PLA particles are able to cross the rat nasal epithelium. These studies indicate that the PEG coating around the particles has a role in stabilizing PLA particles in mucosal fluids and that it facilitates the transport of the nanoencapsulated antigen, hence eliciting a high and long lasting immune response.

Use of the crushing strength parameter for quality control of phenobarbital-microcrystalline cellulose tablets.

Three variables of the tablet manufacturing process (duration of mixing with lubricant, maximum compression force and compression rate) were studied for their effects on various properties of direct compression phenobarbital-microcrystalline cellulose tablets. Mixing time and maximum compression force were found to have a marked influence on friability and dissolution rate; crushing strength was found to be a useful parameter for quality control.

Acetaminophen presystemic biotransformation vs bioavailability in therapeutical dosage range.

The influence of dose on the absorption and presystemic biotransformation of acetaminophen was studied in 15 healthy volunteers after administration of 3 different oral doses (250 mg, 500 mg, 750 mg) following a 3 x 3 Latin Square Design. The analytical method developed (High Performance Liquid Chromatography, HPLC) allows the rapid and simultaneous determination of acetaminophen and its major metabolites (its glucuronide and sulphate conjugates) by direct injection of urine samples. The statistical analysis did not reveal significant differences (alpha < 0.05) among treatments in the percentage of dose excreted and MRT and VRT values. Consequently, our results indicate that the absorption and biotransformation of acetaminophen is not affected by the dose in the usual therapeutical range.