Influence of sex on chronic steroid-induced glaucoma: 24-Weeks follow-up study in rats.

The objective was to evaluate ocular changes based on sex in steroid-induced glaucoma models in rats comparing healthy controls, over 24 weeks follow-up. Eighty-nine Long-Evans rats (38 males and 51 females) with steroid-induced glaucoma were analysed. Two steroid-induced glaucoma models were generated by injecting poly-co-lactic-glycolic acid microspheres loaded with dexamethasone (MMDEX model) and dexamethasone-fibronectin (MMDEXAFIBRO model) into the ocular anterior chamber. Intraocular pressure was measured by rebound tonometer Tonolab®. Neuroretinal function was analysed using dark- and light-adapted electroretinography (Roland consult® RETIanimal ERG), and structure was analysed using optical coherence tomography (OCT Spectralis, Heidelberg® Engineering) using Retina Posterior Pole, Retinal Nerve Fibre Layer and Ganglion Cell Layer protocols over 24 weeks. Males showed statistically (p < 0.05) higher intraocular pressure measurements. In both sexes and models neuroretinal thickness tended to decrease over time. In the MMDEX model, males showed higher IOP values and greatest percentage thickness loss in the Ganglion Cell Layer (p = 0.015). Females receiving MMDEXAFIBRO experienced large fluctuations in thickness, a higher percentage loss (on average) in Retina Posterior Pole (p = 0.035), Retinal Nerve Fibre Layer and Ganglion Cell Layer than aged-matched males, and the highest thickness loss rate by mmHg. Although no difference was found by sex in dark- and light-adapted electroretinography, increased amplitude in photopic negative response was found in MMDEX males and MMDEXAFIBRO females at 12 weeks. Although both glaucoma models used dexamethasone, different intraocular pressure and neuroretinal changes were observed depending on sex and other influential cofactors (fibronectin). Both sex and the induced glaucoma model influenced neuroretinal degeneration.

Long-term corticosteroid-induced chronic glaucoma model produced by intracameral injection of dexamethasone-loaded PLGA microspheres.

PURPOSE: To evaluate a new chronic glaucoma model produced by intracameral injection of dexamethasone-loaded poly lactic-co-glycolic acid microspheres (Dex-PLGA-Ms) over six months. METHODS: Healthy rats received two injections (at baseline and Week 4) of Dex-PLGA-Ms into the anterior chamber of the right eye. Clinical signs and intraocular pressure (IOP) were weekly recorded. The structure of the retina and optic nerve was in vivo evaluated using optical coherence tomography (OCT) every two weeks and functionally using dark- and light-adapted electroretinography at 0-12-24 weeks. Histological studies were also performed. RESULTS: IOP progressively increased up to hypertension (23.22 ± 3.63 mmHg) in both eyes but did so later in left eyes. OCT quantified a decrease in full-thickness retina posterior pole (R), retinal-nerve-fiber layer (RNFL), and ganglion-cell layer (GCL) thickness up to 24 weeks. Right eyes showed higher neuroretinal thickness loss up to week 8. RNFL experienced the highest percentage thickness loss at the inferior-superior axis, while in GCL the inner sectors of the horizontal axis (Nasal-Temporal) suffered the greatest decrease in thickness. Retinal ganglion cell, photoreceptor, and intermediate cell functionality decreased over time. Increased deposition of collagen IV was also found in zonular fibers and the ciliary body. CONCLUSIONS: This work shows the usefulness of drug delivery systems, not to treat pathology but to induce it. Only two injections of Dex-PLGA-Ms in the anterior chamber of rat eyes were enough to progressively create ocular hypertension and subsequent functional and structural neuroretinal degeneration, at least over 6 months.

Simultaneous co-delivery of neuroprotective drugs from multi-loaded PLGA microspheres for the treatment of glaucoma.

Glaucoma is a multifactorial neurodegenerative disorder and one of the leading causes of irreversible blindness globally and for which intraocular pressure is the only modifiable risk factor. Although neuroprotective therapies have been suggested to have therapeutic potential, drug delivery for the treatment of ocular disorders such as glaucoma remains an unmet clinical need, further complicated by poor patient compliance with topically applied treatments. In the present study we describe the development of multi-loaded PLGA-microspheres (MSs) incorporating three recognised neuroprotective agents (dexamethasone (DX), melatonin (MEL) and coenzyme Q10 (CoQ10)) in a single formulation (DMQ-MSs) to create a novel sustained-release intraocular drug delivery system (IODDS) for the treatment of glaucoma. MSs were spherical, with a mean particle size of 29.04 ±â€¯1.89 µm rendering them suitable for intravitreal injection using conventional 25G-32G needles. >62% incorporation efficiency was achieved for the three drug cargo and MSs were able to co-deliver the encapsulated active compounds in a sustained manner over 30-days with low burst release. In vitro studies showed DMQ-MSs to be neuroprotective in a glutamate-induced cytotoxicity model (IC50 10.00 ±â€¯0.94 mM versus 6.89 ±â€¯0.82 mM in absence of DMQ-MSs) in R28 cell line. In vivo efficacy studies were performed using a well-established rodent model of chronic ocular hypertension (OHT), comparing single intravitreal injections of microspheres of DMQ-MSs to their equivalent individual single-drug loaded MSs mixture (MSsmix), empty MSs, no-treatment OHT only and naïve groups. Twenty one days after OHT induction, DMQ-MSs showed a significantly neuroprotective effect on RGCs compared to OHT only controls. No such protective effect was observed in empty MSs and single-drug MSs treated groups. This work suggests that multi-loaded PLGA MSs present a novel therapeutic approach in the management of retinal neurodegeneration conditions such as glaucoma.

Pharmaceutical microscale and nanoscale approaches for efficient treatment of ocular diseases.

Efficient treatment of ocular diseases can be achieved thanks to the proper use of ophthalmic formulations based on emerging pharmaceutical approaches. Among them, microtechnology and nanotechnology strategies are of great interest in the development of novel drug delivery systems to be used for ocular therapy. The location of the target site in the eye as well as the ophthalmic disease will determine the route of administration (topical, intraocular, periocular, and suprachoroidal administration) and the most adequate device. In this review, we discuss the use of colloidal pharmaceutical systems (nanoparticles, liposomes, niosomes, dendrimers, and microemulsions), microparticles (microcapsules and microspheres), and hybrid systems (combination of different strategies) in the treatment of ophthalmic diseases. Emphasis has been placed in the therapeutic significance of each drug delivery system for clinical translation.

Novel Water-Soluble Mucoadhesive Carbosilane Dendrimers for Ocular Administration.

The purpose of this research was to determine the potential use of water-soluble anionic and cationic carbosilane dendrimers (generations 1-3) as mucoadhesive polymers in eyedrop formulations. Cationic carbosilane dendrimers decorated with ammonium -NH3(+) groups were prepared by hydrosylilation of Boc-protected allylamine and followed by deprotection with HCl. Anionic carbosilane dendrimers with terminal carboxylate groups were also employed in this study. In vitro and in vivo tolerance studies were performed in human ocular epithelial cell lines and rabbit eyes respectively. The interaction of dendrimers with transmembrane ocular mucins was evaluated with a surface biosensor. As proof of concept, the hypotensive effect of a carbosilane dendrimer eyedrop formulation containing acetazolamide (ACZ), a poorly water-soluble drug with limited ocular penetration, was tested after instillation in normotensive rabbits. The methodology used to synthesize cationic dendrimers avoids the difficulty of obtaining neutral -NH2 dendrimers that require harsher reaction conditions and also present high aggregation tendency. Tolerance studies demonstrated that both prototypes of water-soluble anionic and cationic carbosilane dendrimers were well tolerated in a range of concentrations between 5 and 10 µM. Permanent interactions between cationic carbosilane dendrimers and ocular mucins were observed using biosensor assays, predominantly for the generation-three (G3) dendrimer. An eyedrop formulation containing G3 cationic carbosilane dendrimers (5 µM) and ACZ (0.07%) (289.4 mOsm; 5.6 pH; 41.7 mN/m) induced a rapid (onset time 1 h) and extended (up to 7 h) hypotensive effect, and led to a significant increment in the efficacy determined by AUC0(8h) and maximal intraocular pressure reduction. This work takes advantage of the high-affinity interaction between cationic carbosilane dendrimers and ocular transmembrane mucins, as well as the tensioactive behavior observed for these polymers. Our results indicate that low amounts of cationic carbosilane dendrimers are well tolerated and able to improve the hypotensive effect of an acetazolamide solution. Our results suggest that carbosilane dendrimers can be used in a safe range of concentrations to enhance the bioavailability of drugs topically administered in the eye.

Preservation of biological activity of glial cell line-derived neurotrophic factor (GDNF) after microencapsulation and sterilization by gamma irradiation.

A main issue in controlled delivery of biotechnological products from injectable biodegradable microspheres is to preserve their integrity and functional activity after the microencapsulation process and final sterilization. The present experimental work tested different technological approaches to maintain the biological activity of an encapsulated biotechnological product within PLGA [poly (lactic-co-glycolic acid)] microspheres (MS) after their sterilization by gamma irradiation. GDNF (glial cell line-derived neurotrophic factor), useful in the treatment of several neurodegenerative diseases, was chosen as a labile model protein. In the particular case of optic nerve degeneration, GDNF has been demonstrated to improve the damaged retinal ganglion cells (RGC) survival. GDNF was encapsulated in its molecular state by the water-in-oil-in-water (W/O/W) technique or as solid according to the solid-in-oil-in-water (S/O/W) method. Based on the S/O/W technique, GDNF was included in the PLGA microspheres alone (S/O/W 1) or in combination with an antioxidant (vitamin E, Vit E) (S/O/W 2). Microspheres were sterilized by gamma-irradiation (dose of 25 kGy) at room and low (-78 °C) temperatures. Functional activity of GDNF released from the different microspheres was evaluated both before and after sterilization in their potential target cells (retinal cells). Although none of the systems proposed achieved with the goal of totally retain the structural stability of the GDNF-dimer, the protein released from the S/O/W 2 microspheres was clearly the most biologically active, showing significantly less retinal cell death than that released from either W/O/W or S/O/W 1 particles, even in low amounts of the neurotrophic factor. According to the results presented in this work, the biological activity of biotechnological products after microencapsulation and sterilization can be further preserved by the inclusion of the active molecule in its solid state in combination with antioxidants and using low temperature (-78 °C) during gamma irradiation exposure.

Interfacial interaction between transmembrane ocular mucins and adhesive polymers and dendrimers analyzed by surface plasmon resonance.

PURPOSE: Development of the first in vitro method based on biosensor chip technology designed for probing the interfacial interaction phenomena between transmembrane ocular mucins and adhesive polymers and dendrimers intended for ophthalmic administration. METHODS: The surface plasmon resonance (SPR) technique was used. A transmembrane ocular mucin surface was prepared on the chip surface and characterized by QCM-D (Quartz Crystal Microbalance with Dissipation) and XPS (X-ray photoelectron spectroscopy). The mucoadhesive molecules tested were: hyaluronic acid (HA), carboxymethyl cellulose (CMC), hydroxypropylmethyl cellulose (HPMC), chitosan (Ch) and polyamidoamine dendrimers (PAMAM). RESULTS: While Ch originated interfacial interaction with ocular transmembrane mucins, for HA, CMC and HPMC, chain interdiffusion seemed to be mandatory for bioadherence at the concentrations used in ophthalmic clinical practise. Interestingly, PAMAM dendrimers developed permanent interfacial interactions with transmembrane ocular mucins whatever their surface chemical groups, showing a relevant importance of co-operative effect of these multivalent systems. Polymers developed interfacial interactions with ocular membrane-associated mucins in the following order: Ch(1 %) > G4PAMAM-NH(2)(2 %) = G4PAMAM-OH(2 %) > G3.5PAMAM-COOH(2 %)>> CMC(0.5 %) = HA(0.2 %) = HPMC(0.3 %). CONCLUSIONS: The method proposed is useful to discern between the mucin-polymer chemical interactions at molecular scale. Results reinforce the usefulness of chitosan and dendrimers as polymers able to increase the retention time of drugs on the ocular surface and hence their bioavailability.

Aplicación de la metodología de aprendizaje cooperativo a la materia de Biofarmacia y Farmacocinética / Implementation of the cooperative learning methodology to the Biopharmaceutics and Pharmacokinetics subject

La convergencia dentro del marco Europeo de Educación Superior plantea la necesidad de introducir cambios en el sistema educativo universitario. En este sentido, la formación en la universidad debe asegurar el desarrollo integral y continuo de los nuevos profesionales. El modelo tradicional de enseñanza ligado a conocimientos disciplinares ha de sustituirse por una formación en competencias ligadas al desempeño profesional y a un saber hacer cualificado para cada situación concreta. Metodologías activas como el aprendizaje cooperativo (AC) son reconocidas como estrategias idóneas para alcanzar estas competencias.En este entorno se plantea el objetivo de este trabajo como una experiencia de aprendizaje cooperativo que se está llevando a cabo con un grupo de alumnos de la asignatura de Biofarmacia y Farmacocinética en la Licenciatura de Farmacia. Este estudio forma parte del desarrollo de un proyecto de Innovación y Mejora de la Calidad Docente de la Universidad Complutense de Madrid (UCM 2009-276). Dentro del programa de la asignatura se han elegido aquellos temas que resultan más adecuados para los objetivos de esta modalidad de aprendizaje. El grupo en el que se ha llevado a cabo esta experiencia, es un grupo piloto (adscripción voluntaria para los alumnos) que cuenta con 63 alumnos. Se han formado 9 grupos de trabajo con la participación de 7 especialistas por grupo. Para la comunicación con los alumnos y la entrega de documentación de trabajo se ha utilizado el Campus Virtual de la UCM que utiliza la plataforma WebCT(AU)

The convergence in the European Higher Education Framework presents the need to make changes in the University Educational System. In this sense, the education in the University must ensure the all-round and continuous development of new professionals. The traditional model of education related to the knowledge of subjects must be substituted by the education in competences related to professional performance and qualification know-how for each particular situation. Active methodologies such as cooperative learning are recognized as suitable strategies to get those competences. In this environment, the objective of this work is presented as a cooperative learning experience that is carrying out with a group of students of Biopharmacy and Pharmacokinetic subject of the Pharmacy Grade. This study is part of the development of a Project of Innovation and Improvement of the Educational Quality in the Complutense University of Madrid. The topics that have been chosen from the whole program of the subject are the most suitable to reach the objectives of this learning method. This experience has been tested in a pilot group integrated by 63 voluntary students. Nine work groups have been formed with the participation of seven specialists in each group. The UCM Virtual Campus website (based on WebCT platform) has been used for communication with the students and documentation purposes(AU)

Specific permeability modulation of intestinal paracellular pathway by chitosan-poly(isobutylcyanoacrylate) core-shell nanoparticles.

This work is focused on the evaluation of the in vitro permeation modulation of chitosan and thiolated chitosan (chitosan-TBA) coated poly(isobutylcyanoacrylate) (PIBCA) nanoparticles as drug carriers for mucosal administration. Core-corona nanoparticles were obtained by radical emulsion polymerisation of isobutylcyanoacrylate (IBCA) with chitosan of different molecular weights and different proportions of chitosan/chitosan-TBA. In this work, the effect of these nanoparticles on the paracellular permeability of intestinal epithelium was investigated using the Ussing chamber technique, by adding nanoparticle suspensions in the mucosal side of rat intestinal mucosa. Results showed that permeation of the tracer [14C]mannitol and the reduction of transepithelial electrical resistance (TEER) in presence of nanoparticles were more pronounced in those formulations prepared with intermediate amounts of thiolated polymer. This effect was explained thanks to the high diffusion capacity of those nanoparticles through the mucus layer that allowed them to reach the tight junctions in higher extent. It was concluded that, although a first contact between nanoparticles and mucus was a mandatory condition for the development of a permeation enhancement effect, the optimal effect depended on the chitosan/chitosan-TBA balance and the conformational structure of the particles shell.

Drug release behaviour from methyl methacrylate-starch matrix tablets: effect of polymer moisture content.

The aim of this work was to study the effect of the initial moisture content of the polymer on the tabletting and drug release behaviour of controlled release inert matrices elaborated with methyl methacrylate (MMA)-starch copolymers. The copolymers, obtained by free radical polymerisation and dried by two different methods (oven-drying or freeze-drying), were equilibrated at different relative humidities (0%, 25%, 50% and 75% RH) at room temperature. From these copolymers, matrix systems were directly compressed containing either a slightly water-soluble drug (anhydrous theophylline) or a freely water-soluble drug (salbutamol sulphate), and their compaction properties and in vitro dissolution profiles were evaluated. The release profiles were compared following model-independent methods, such as the Qt parameter and the similarity factor f2. Moreover, several kinetic models were employed to evaluate the possible changes in the release mechanism. For anhydrous theophylline, the initial moisture content of the copolymers did not affect the release characteristics from the inert matrices under study, and a typical Fickian diffusion mechanism was observed for the different formulations. However, in case of salbutamol sulphate, the presence of moisture might induce a fast drug dissolution, promoting the weakness of the matrix structure and hence, its partial disintegration. So, an "anomalous" mixed phenomenon of diffusion and erosion was found, influenced by the initial moisture content of the copolymer.

Characterization of chitosan thiolation and application to thiol quantification onto nanoparticle surface.

The objective of the present work was to establish a simple and appropriated method for the quantification of thiol groups standing on the surface of core-shell nanoparticles elaborated with poly(isobutyl cyanoacrylates) and thiolated chitosan. A critical analysis of the widely used Ellman's method for the determination of thiol groups in various compounds was made. The reduced solubility of the thiolated polymer at the optimal pH of the Ellman's assay (pH 8-8.5) made difficult the accessibility of the Ellman's reagent to thiol groups in the cross-linked polymer. Furthermore, the lack of stability of the Ellman's reaction with time lead to the conclusion that the Ellman's method was of limited value to evaluate thiol groups in thiolated polymers like thiolated chitosan. An alternative and very simple thiol quantification method was developed on the bases of the classical iodine titration. The new method allowed the determination of thiol groups in small amount of samples at acidic pH, and the monitoring of the thiol determination kinetic with time. It was successfully applied to the quantification of active thiol groups on the surface of poly(isobutyl cyanoacrylates) nanoparticles coated with thiol chitosan.

In vitro evaluation of calcium binding capacity of chitosan and thiolated chitosan poly(isobutyl cyanoacrylate) core-shell nanoparticles.

The ability of chitosan and its derivatives to bind cations is well known. Chitosan and thiolated chitosan were recently associated with poly(isobutyl cyanoacrylate) (PIBCA) nanoparticles leading to very promising results in terms of bioadhesion and permeation enhancement properties. Taking into account the influence that cations concentration have in the maintenance of both the permeation and the enzymatic barrier of the oral route, the possible cation binding capacity of these colloidal systems might be interesting in the use of these nanocarriers for the oral administration of pharmacologically active peptides. The aim of the present work was to in vitro evaluate the capacity of these colloidal systems to bind calcium, a model cation of physiological interest in the intestinal tract. The presence of chitosan on the nanoparticle surface importantly increased the calcium binding ability, in comparison to non-coated PIBCA nanoparticles. In addition, its presentation in the gel layer surrounding the nanoparticles, also beneficiated its binding capacity, obtaining 2-3 folds higher values when the polymer coated the nanoparticles than when it was in solution. The cross-linked structure observed for thiolated chitosan, due to the formation of inter- and intra-chain disulphide bonds, diminished the accessibility of cation to active sites of the polymer, decreasing the binding capacity of the calcium ion. However, when the amount of free thiol groups on the nanoparticle surface was high enough, the binding behaviour observed was higher than for nanoparticles elaborated with non-modified polymer.

Potencial de dendrímeros como vehículos de fármacos en oftalmología / Potential of dendrimers as drug carriers in ophthalmology

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Influence of moisture content on the mechanical properties of methyl methacrylate-starch copolymers.

The water vapour sorption-desorption behaviour of graft copolymers (hydroxypropylstarch-methyl methacrylate -HSMMA- and carboxymethylstarch-methyl methacrylate -CSMMA-) synthetised by free-radical polymerisation and alternatively dried by oven (OD) or freeze-drying (FD) techniques was investigated in a previous paper. The aim of the present study was to analyse the influence of the amount and distribution of water molecules on the flow and compaction characteristics of this family of methyl methacrylate-starch copolymers. Products were stored at constant temperature (25 degrees C) and different relative humidity conditions (RH). Flow properties of the powdered materials were evaluated using glass and stainless-steel funnels and the densification behaviour was studied in detail by means of Heckel treatment and compression parameters. Results revealed that the storage at 25-50% RH was the optimum condition relating flowability for HSMMA and OD-CSMMA copolymers. At higher RH values, the flow characteristics worsened, due to an increment in cohesive forces. Compaction experiments showed that the 25-50% RH range improved also the compression performance of the copolymers, due to increasing powder compressibility and reduced compact relaxation. Under these circumstances, absorbed water might act as plasticiser and adsorbed water as lubricant.

Tuning of shell and core characteristics of chitosan-decorated acrylic nanoparticles.

The aim of the work was to develop a new family of chitosan-coated acrylic nanoparticles to increase the specificity of absorption of drugs associated given by the mucosal route. To achieve this goal, techniques of radical and anionic emulsion polymerisation of isobutylcyanoacrylate (IBCA) were used. Changes in the shell composition were made by using chitosan of different molecular weight and thiolated chitosan to modify the particle surface properties in order to vary the mucosae-nanoparticle interactions. The core was also modified by the inclusion of methyl methacrylate (MMA) as second monomer potentially able to improve the control of drug release. Finally, the labelling of nanoparticles core with a fluorophore, methacryloxyethyl thiocarbamoyl rhodamine B (Polyfluor), was successfully achieved, necessary for the in vitro and in vivo evaluation of the systems created. Results showed that nanoparticle size varied from 200 to 500 nm, depending on the molecular weight of chitosan used. Positive surface charge values were obtained in all cases. In addition, evidences of the presence of thiol groups were obtained (0.03-0.16 x 10(-3)micromol/cm(2) of nanoparticle).

Water sorption-desorption behaviour of methyl methacrylate-starch copolymers: effect of hydrophobic graft and drying method.

A new family of graft copolymers combining hydrophilic and hydrophobic components have recently been proposed as direct compression excipients. Copolymers were synthetised by free radical copolymerisation of starch derivatives with methyl methacrylate (MMA) and were alternatively dried by oven or freeze-drying techniques. The aim of this study was to investigate the water vapour sorption-desorption behaviour of these copolymers, focusing on the influence of variables such as the hydrophobic component and the drying process. Moisture sorption and desorption isotherms were measured at 25 degrees C and analysed according to GAB and Young-Nelson equations, which distinguish between different physical forms of moisture distribution. The Young-Nelson model gave the best fit to the experimental data. The results obtained showed that the presence of the acrylic component modified not only the total hygroscopicity of the copolymers, as compared with the original starch derivatives, but also the water distribution in the solid, which might have an important role in the effect of moisture content on copolymer characteristics. The main water-sorption mechanism seemed to be absorption into the copolymer particles structure, in agreement with their starching nature. In terms of water sorption-desorption characteristics, no marked differences were found between the two drying methods used.

Interacción sólido-agua. III. Efecto de la presencia de humedad sobre las características tecnológicas de comprimidos / Solid-water interaction III. Effect of moisture content on the technological characteristics of tablets

La presencia de agua puede afectar de forma importante las características tecnológicas básicas de los sólidos pulverulentos y de los comprimidos elaborados con ellos. Así, el agua adsorbida en la superficie de las partículas puede actuar como lubrificante mejorando la fluidez y la densificación por reordenamiento durante la compresión. En mayores cantidades, este agua adsorbida favorece la formación de aglomerados, que si bien empeora el flujo del sólido, favorece el acercamiento de las partículas y por tanto la formación de uniones durante la compresión. Un exceso de agua superficial conlleva la disminución en la formación de dichas uniones por su efecto como contaminante de superficie y por la generación de resistencia hidrodinámica. Por otro lado, el agua absorbida en el interior de las partículas puede ejercer un efecto plastificante que aumenta las fuerzas de cohesión y adhesión del sólido y por tanto empeora las características de fluidez, aunque favorece de forma importante la consolidación por deformación. Este efecto también se manifestará en las características finales de los comprimidos obtenidos, pudiendo modificarse algunos de sus parámetros más fundamentales como su resistencia a la rotura, su porcentaje de friabilidad, etc (AU)

Interacción sólido-agua. I. Estudio de las interacciones del agua con los sólidos farmacéuticos / Solid-water interaction. I. Study of water-pharmaceutical interactions

Se lleva a cabo una revisión de las interacciones que se establecen entre las moléculas de agua y los sólidos pulverulentos utilizados en farmacia según su naturaleza. Así, en un sólido cristalino el agua puede unirse de forma débil a la superficie del cristal o bien acceder al interior de su estructura, suponiendo generalmente una cantidad de agua muy pequeña, excepto en el caso de cristales hidratos de alto orden. Por su parte, los sólidos amorfos presentan una captación de agua o sorción generalmente más elevada y claramente no estequiométrica, que está en función de múltiples factores como su hidrofilia o las condiciones ambientales externas. Esta presencia de agua puede alterar profundamente las características tanto de principios activos como de excipientes, haciéndose necesario un conocimiento y control de dicho factor. Seguidamente se aborda el estudio de las distintas técnicas disponibles, tanto cualitativas como cuantitativas, para la determinación de la cantidad de agua presente en un sólido (AU)