Drug Dissolution Behavior Research Articles

A Comparative Study of the Use of Mesoporous Carbon and Mesoporous Silica as Drug Carriers for Oral Delivery of the Water-Insoluble Drug Carvedilol.

Mesoporous carriers have been extensively applied to improve the dissolution velocity and bioavailability of insoluble drugs. The goal of this work was to compare the drug-loading efficiency (LE) and drug-dissolution properties of mesoporous silica nanoparticles (MSN) and mesoporous carbon nanoparticles (MCN) as drug vectors oral delivery of water-insoluble drugs. For this purpose, MSN and MCN with similar particle size, surface area, and mesoporous diameter were prepared to precisely evaluate the effects of different textures on the drug-loading and dissolution behavior of insoluble drugs. Carvedilol (CAR), a Bio-pharmaceutic Classification System (BCS) class II drug, was loaded in the MSN and MCN by the solvent adsorption method and solvent evaporation method with different carrier–drug ratios. The carboxylated MCN (MCN–COOH) had a higher LE for CAR than MSN for both the two loading methods due to the strong adsorption effect and π–π stacking force with CAR. In vitro drug dissolution study showed that both MSN and MCN-COOH could improve the dissolution rate of CAR compared with the micronized CAR. In comparison to MSN, MCN-COOH displayed a slightly slower dissolution profile, which may be ascribed to the strong interaction between MCN-COOH and CAR. Observation of cell cytotoxicity and gastrointestinal mucosa irritation demonstrated the good biocompatibility of both MSN and MCN–COOH. The present study encourages further research of different carriers to determine their potential application in oral administration.

Development of Novel Functional Formulations Based on Pharmaceutical Technologies

After 32 years as a researcher in a pharmaceutical company, the author has served as a professor in the Development of Pharmaceutical Engineering and Drug Delivery Science at University of Shizuoka for the past 11 years. The research I was involved in can be categorized into four main items. First, the crystal transformation of clarithromycin (CAM) was focused on to develop the CAM high-loaded sustained release and gastro-floating formulations. Furthermore, the stabilization mechanism of CAM in the gastro-intestinal tract was clarified to elucidate gel formation under conditions of low pH. Second, the development of novel dosage regimens and optimization of formulation design were carried out using powder technology. In this category, a wax matrix formulation for taste masking, highly drug-loaded fine globular granules using a multi-functional rotor processor, and orally disintegrating tablets treated with microwave or high-pressure carbon dioxide were our targets. The third category was the manufacture of dispersion systems including lipid nanoparticles and cubosomes in order to improve the bioavailability and stability of poorly water-soluble drugs. The fourth category was the development and application of novel physical testing methods including investigation of the internal structure of fine granules using microtomography with synchrotron X-ray radiation, dissolution of spherical granules under non-sink conditions, mathematical models to analyze the dissolution behavior of metastable crystals or amorphous drugs and prediction of the available surface area of tablets during dissolution process.

Design expert assisted mathematical optimization of solubility and study of fast disintegrating tablets of Lercanidipine Hydrochloride

90% of drugs being researched today, posses poor solubility setback which inturn renders the drug with slower rate of absorption from the buccal route; hence dissolution is the rate limiting step for such lipophilic drugs. So, there is a need to keep a check on the dissolution profile of these drugs to ensure maximum therapeutic utilization. The dissolution rate therefore becomes a primary factor which governs the rate and extent of its absorption. Enormous work is being performed in the field of enhancement of solubility and dissolution behaviour of such drugs. Advancements and innovations have developed solid dispersion (SD) technique as the novel method for the solubility enhancement. Precision of dosing and patient's compliance is a crucial prerequisite for the management of chronic Antihypertensive treatment, So there arised a need to formulate a system which should resolve the difficulties associated with conventional tablets. This issue can be better tackled with the formulation of orally fast disintegrating tablets. The aim of the present study was to improve the solubility and dissolution rate of Lercanidipine hydrochloride (LRH) by formulating a solid dispersion with Polyvinyl pyrollidine (PVP-K30) and Guargum. Full Factorial designs are exploited to learn and research the effects of different variables on the quality determinant parameters. An appropriate statistical model was selected for the scrutiny of the enhanced dissolution pattern. Finally, these solid dispersions were incorporated into fast disintegrating tablets.
 Keywords: Lercanidipine Hydrochloride, Solid dispersion, Statistical design approach, Melt fusion method, Fast disintegrating tablet, In vivo studies

Physiological parameters of the gastrointestinal fluid impact the dissolution behavior of the BCS class IIa drug valsartan

The objective of this study was to investigate the effect of the physiological parameters (pH, buffer capacity, and ionic strength) of the gastrointestinal (GI) fluid on the dissolution behavior of the class II weakly acidic (BCS class IIa) drug valsartan. A series of in vitro dissolution studies was carried out on Diovan® immediate release tablets using media that cover the physiological range of pH (1.2–7.8), buffer capacity (0–0.047 M/ΔpH), and ionic strength (0–0.4 mol/L) of the GI fluid during fasted and fed states using the conventional USP II apparatus. Valsartan exhibited pH- and buffer capacity-dependent dissolution behavior, where valsartan release was slow and incomplete in media simulating gastric fluid with low pH, and fast and complete in media simulating intestinal fluid with high pH. In addition, the rate of valsartan release increased with increasing the buffer capacity of the dissolution medium. In water and NaCl solutions, valsartan release was incomplete and the dissolution profiles were similar regardless of the ionic strength of the medium, indicating an ionic strength-independent dissolution behavior. These results highlight the significant effect of the physiological parameters of the GI fluid on the dissolution behavior of BCS class IIa drugs.

Ornidazole-loaded polyethylene glycol-based micron-level particles: influence of eutectic liquid on reservoir-type particle formation, drug entrapment efficiency and drug dissolution or release behavior

A temperature-controlled dispersion technique was used to develop ornidazole-loaded micron-level particles. To overcome the problem of generating the reservoir-type particles from polyethylene glycol, the influence of camphor and menthol (1:1 ratio)-based eutectic liquid on reservoir-type particle formation, drug entrapment efficiency and drug release behavior was examined. A distinct wall formation was observed for the particles on contact with water. Higher drug entrapment efficiency (~ 15–20%) was noted for the particles prepared with eutectic liquid. Significantly, (one-way ANOVA) higher t50% values (35.16 ± 1.44 min for HCl and 43.6 ± 0.76 min for pH 6.8 phosphate buffer) were noticed for the eutectic liquid-based particles in comparison with the t50% values (30.66 ± 0.76 min for HCl and 35.5 ± 0.86 min for pH 6.8 phosphate buffer) observed for the particles made without the same. The potential of eutectic liquid to generate the microcapsule structure should be explored further.

Development and in vitro evaluation of pH-independent release matrix tablet of weakly acidic drug valsartan using quality by design tools

The main objective of this study was the development of pH-independent controlled release valsartan matrix tablet in Quality by design (QbD) framework. The quality target product profile (QTPP), critical quality attributes (CQAs) and critical material attributes (CMAs) were defined by science and risk-based methodologies. Potential risk factors were identified with Fishbone diagram. Following, CMAs were further investigated with a semi-quantitative risk assessment method, which has been revised with mitigated risks after development and optimization studies. According to defined critical material attributes, which one of them was determined to be the dissolution, formulation optimization study was performed by using a statistical design of experiment. Formulation variables have been identified and fixed first with a ‘One factor at a time (OFAT)’ approach. After OFAT studies, a statistical experimental design was conducted with the most critical material attributes. Statistical design space and mathematical prediction equations have been developed for dissolution and hardness, which is important to predict drug dissolution behavior. In conclusion, a pH-independent release has been achieved for weakly acidic drug valsartan with a deeper understanding of drug product quality, with the science and risk-based approaches of QbD tools.

Efficient production of solid dispersions by spray drying solutions of high solid content using a 3-fluid nozzle

To evaluate the feasibility of producing solid dispersions with 3-fluid nozzle spray drying to improve the dissolution behavior of lipophilic drugs, 60 experiments were performed based on a Design of Experiment. Solid dispersions with mannitol as a hydrophilic matrix and diazepam as a model drug with a drug load of 20 wt-% were produced. The variables of the experiments were the water/organic solvent ratio, liquid feed flow, total solid content, atomizing airflow and type of organic solvent (ethanol or ethyl acetate). The responses measured were dissolution rate, yield, actual drug load, particle size and crystallinity of diazepam and mannitol. Increasing water/organic solvent ratio was found to be the main factor for enhancing the dissolution rate. The total solid content of the solutions to be spray dried did not affect any of the responses, which means that processing solutions of high concentrations is possible. The choice of organic solvent did not affect the responses as well, i.e. both the fully water miscible solvent ethanol and the poorly water miscible solvent ethyl acetate could be used which makes this production method highly versatile.

Designing and monitoring microstructural properties of oligosaccharide/co-solvent ternary complex particles to improve benznidazole dissolution

Benznidazole (BNZ) is the main drug used for the treatment of Chagas disease. However, its low aqueous solubility limits its efficacy. In this study, we have prepared host–guest inclusion complexes of BNZ with beta-cyclodextrin (β-CD) in solid phase and assessed the influence of the co-solvents triethanolamine (TEA) and 1-methyl-2-pyrrolidone (NMP) for improving the drug dissolution performance. The physicochemical properties of prepared spray-dried (SD) particles and physical mixtures (PM) were carefully monitored using FTIR, XRD and SEM images. The used co-solvents affected β-CD–drug interactions, the structural properties and drug dissolution behavior of particles. TEA did not improve the solubilizing effect of β-CD, while NMP was able to enhance drug dissolution performance in both SD and PM complexes. These promising results support the use of specific co-solvents with CD as a new raw material for insoluble compounds. The studied solid dispersions showed promising features to improve BNZ efficacy against Chagas disease.

Spray drying of poorly soluble drugs from aqueous arginine solution

Co-amorphous drug-amino acid mixtures have shown potential for improving the solid-state stability and dissolution behavior of amorphous drugs. In previous studies, however these mixtures have been produced mainly with small-scale preparation methods, or with methods that have required the use of organic solvents or other dissolution enhancers. In the present study, co-amorphous ibuprofen-arginine and indomethacin-arginine mixtures were spray dried from water. The mixtures were prepared at two drug-arginine molar ratios (1:1 and 1:2). The properties of the prepared mixtures were investigated with differential scanning calorimetry, X-ray powder diffractometry, Fourier-transform infrared spectroscopy and a 24h, non-sink, dissolution study. All mixtures exhibited a single glass transition temperature (Tg), evidence of the formation of homogenous single-phase systems. Fourier transform infrared spectroscopy revealed strong interactions (mainly salt formation) that account for the positive deviation between measured and estimated Tg values. No crystallization was observed during a 1-year stability study in either 1:1 or 1:2 mixtures, but in the presence of moisture, handling difficulties were encountered. The formation of co-amorphous salts led to improved dissolution characteristics when compared to the corresponding physical mixtures or to pure crystalline drugs.

Absorption Study of Genistein Using Solid Lipid Microparticles and Nanoparticles: Control of Oral Bioavailability by Particle Sizes.

In this study, the effect of particle size of genistein-loaded solid lipid particulate systems on drug dissolution behavior and oral bioavailability was investigated. Genistein-loaded solid lipid microparticles and nanoparticles were prepared with glyceryl palmitostearate. Except for the particle size, other properties of genistein-loaded solid lipid microparticles and nanoparticles such as particle composition and drug loading efficiency and amount were similarly controlled to mainly evaluate the effect of different particle sizes of the solid lipid particulate systems on drug dissolution behavior and oral bioavailability. The results showed that genistein-loaded solid lipid microparticles and nanoparticles exhibited a considerably increased drug dissolution rate compared to that of genistein bulk powder and suspension. The microparticles gradually released genistein as a function of time while the nanoparticles exhibited a biphasic drug release pattern, showing an initial burst drug release, followed by a sustained release. The oral bioavailability of genistein loaded in solid lipid microparticles and nanoparticles in rats was also significantly enhanced compared to that in bulk powders and the suspension. However, the bioavailability from the microparticles increased more than that from the nanoparticles mainly because the rapid drug dissolution rate and rapid absorption of genistein because of the large surface area of the genistein-solid lipid nanoparticles cleared the drug to a greater extent than the genistein-solid lipid microparticles did. Therefore, the findings of this study suggest that controlling the particle size of solid-lipid particulate systems at a micro-scale would be a promising strategy to increase the oral bioavailability of genistein.

Dropwise additive manufacturing of pharmaceutical products for amorphous and self emulsifying drug delivery systems

The improvements in healthcare systems and the advent of the precision medicine initiative have created the need to develop more innovative manufacturing methods for the delivery and production of individualized dosing and personalized treatments. In accordance with the changes observed in healthcare systems towards more innovative therapies, this paper presents dropwise additive manufacturing of pharmaceutical products (DAMPP) for small scale, distributed manufacturing of individualized dosing as an alternative to conventional manufacturing methods A dropwise additive manufacturing process for amorphous and self-emulsifying drug delivery systems is reported, which utilizes drop-on-demand printing technology for automated and controlled deposition of melt-based formulations onto inert tablets.The advantages of drop on demand technology include reproducible production of droplets with adjustable sizing and high placement accuracy, which enable production of individualized dosing even for low dose and high potency drugs. Flexible use of different formulations, such as lipid-based formulations, allows enhancement of the solubility of poorly water soluble and highly lipophilic drugs with DAMPP. Here, DAMPP is used to produce solid oral dosage forms from melts of an active pharmaceutical ingredient and a surfactant. The dosage forms are analyzed to show the amorphous nature, self-emulsifying drug delivery system characteristics and dissolution behavior of these formulations.

Preparation and Evaluation of Atenolol Floating Beads as a Controlled Delivery System

This study aims to encapsulate atenolol within floating alginate-ethylcellulose beads as an oral controlled-release delivery system using aqueous colloidal polymer dispersion (ACPD) method.To optimize drug entrapment efficiency and dissolution behavior of the prepared beads, different parameters of drug: polymer ratio, polymer mixture ratio, and gelling agent concentration were involved.The prepared beads were investigated with respect to their buoyancy, encapsulation efficiency, and dissolution behavior in the media: 0.1 N HCl (pH 1.2), acetate buffer (pH 4.6) and phosphate buffer (pH 6.8). The release kinetics and mechanism of the drug from the prepared beads was investigated.All prepared atenolol beads remained floating on 0.1 N HCl (pH 1.2) medium over 24 hours. Besides, high yield beads of 73.07- 84.31% was obtained. Encapsulation efficiencies were in the range of 33.10 % -79.04 %, and were found to increase as a function of increasing drug: polymer mixture ratio and the gelling agent concentrations.Moreover, atenolol release profile from the beads was affected by the pH of the dissolution medium. It was found to be slowest in 0.1 N HCl (pH 1.2) and fastest in phosphate buffer (pH 6.8).The obtained results suggest that atenolol could be formulated as a controlled release beads, using ethylcellulose and alginate as polymers, using ACPD method.
 Keywords: Floating beads, Atenolol, Controlled Delivery System

Mathematical model to analyze the dissolution behavior of metastable crystals or amorphous drug accompanied with a solid-liquid interface reaction

Metastable crystals and the amorphous state of poorly water-soluble drugs in solid dispersions (SDs), are subject to a solid-liquid interface reaction upon exposure to a solvent. The dissolution behavior during the solid-liquid interface reaction often shows that the concentration of drugs is supersaturated, with a high initial drug concentration compared with the solubility of stable crystals but finally approaching the latter solubility with time. However, a method for measuring the precipitation rate of stable crystals and/or the potential solubility of metastable crystals or amorphous drugs has not been established. In this study, a novel mathematical model that can represent the dissolution behavior of the solid-liquid interface reaction for metastable crystals or amorphous drug was developed and its validity was evaluated. The theory for this model was based on the Noyes-Whitney equation and assumes that the precipitation of stable crystals at the solid-liquid interface occurs through a first-order reaction. Moreover, two models were developed, one assuming that the surface area of the drug remains constant because of the presence of excess drug in the bulk and the other that the surface area changes in time-dependency because of agglomeration of the drug. SDs of Ibuprofen (IB)/polyvinylpyrrolidone (PVP) were prepared and their dissolution behaviors under non-sink conditions were fitted by the models to evaluate improvements in solubility. The model assuming time-dependent surface area showed good agreement with experimental values. Furthermore, by applying the model to the dissolution profile, parameters such as the precipitation rate and the potential solubility of the amorphous drug were successfully calculated. In addition, it was shown that the improvement in solubility with supersaturation was able to be evaluated quantitatively using this model. Therefore, this mathematical model would be a useful tool to quantitatively determine the supersaturation concentration of a metastable drug from solid dispersions.

Gelation Factors of Pectin for Development of a Powder Form of Gel, Dry Jelly, as a Novel Dosage Form.

Jellies for oral administration are dosage forms that contain water, as stipulated in the Japanese Pharmacopeia, and heat is generally applied to the jellies during the manufacturing process. Therefore, it is difficult to formulate drugs that may be affected adversely by water and/or heat. To solve this problem, we tried to develop a powder form of gel as a novel dosage form (dry jelly: jelly medicine extemporaneously prepared) that is converted to jelly after addition of water at the time of administration. For this purpose, a basic gel formulation consisting of pectin, glucono-δ-lactone, dibasic calcium phosphate hydrate, and sucrose was investigated to evaluate the critical factors affecting gelation phenomena. The gel form was developed by adjusting the amount of each component of the formulation and of water added. Gelation occurred even with hard water containing metal ions (hardness of approximately 304 mg/L), and no changes in gel hardness occurred. The desired gel hardness could be controlled by adjusting the amount of water. The gel hardness changed over time after the addition of water, but this change did not affect the dissolution behavior of drugs formulated in the dry jelly.

Preparation and physicochemical characterization of spray-dried and jet-milled microparticles containing bosentan hydrate for dry powder inhalation aerosols.

The objectives of this study were to prepare bosentan hydrate (BST) microparticles as dry powder inhalations (DPIs) via spray drying and jet milling under various parameters, to comprehensively characterize the physicochemical properties of the BST hydrate microparticles, and to evaluate the aerosol dispersion performance and dissolution behavior as DPIs. The BST microparticles were successfully prepared for DPIs by spray drying from feeding solution concentrations of 1%, 3%, and 5% (w/v) and by jet milling at grinding pressures of 2, 3, and 4 MPa. The physicochemical properties of the spray-dried (SD) and jet-milled (JM) microparticles were determined via scanning electron microscopy, atomic force microscopy, dynamic light scattering particle size analysis, Karl Fischer titration, surface analysis, pycnometry, differential scanning calorimetry, powder X-ray diffraction, and Fourier transform infrared spectroscopy. The in vitro aerosol dispersion performance and drug dissolution behavior were evaluated using an Anderson cascade impactor and a Franz diffusion cell, respectively. The JM microparticles exhibited an irregular corrugated surface and a crystalline solid state, while the SD microparticles were spherical with a smooth surface and an amorphous solid state. Thus, the in vitro aerosol dispersion performance and dissolution behavior as DPIs were considerably different due to the differences in the physicochemical properties of the SD and JM microparticles. In particular, the highest grinding pressures under jet milling exhibited excellent aerosol dispersion performance with statistically higher values of 56.8%±2.0% of respirable fraction and 33.8%±2.3% of fine particle fraction and lower mass median aerodynamic diameter of 5.0±0.3 μm than the others (P<0.05, analysis of variance/Tukey). The drug dissolution mechanism was also affected by the physicochemical properties that determine the dissolution kinetics of the SD and JM microparticles, which were well fitted into the Higuchi and zero-order models, respectively.

Fused-filament 3D printing of drug products: Microstructure analysis and drug release characteristics of PVA-based caplets

Fused deposition modeling (FDM) 3–Dimensional (3D) printing is becoming an increasingly important technology in the pharmaceutical sciences, since it allows the manufacture of personalized oral dosage forms by deposition of thin layers of material. Here, a filament extruder was used to obtain filaments of polyvinyl alcohol (PVA) containing paracetamol or caffeine appropriate for 3D printing. The filaments were used to manufacture caplets for oral administration by FDM 3D printing, with the aim of evaluating the effect of the internal structure (micropore volume), drug loading and composition on drug dissolution behaviour. Micropore volume of the caplets was primarily determined by the presence of large pores due to gaps in the printed layers/net while printing, and the porosity of the caplets was 10 fold higher than the porosity of the extruded filament. Dynamic dissolution drug release tests on the caplets in biorelevant bicarbonate media revealed distinctive release profiles, which were dependent on drug solubility and drug loading. Porosity of the caplets did not help to predict the different drug release profiles. This study confirms the potential of 3D printing to fabricate caplets and helps to elucidate which factors influence drug release from this type of new dosage form.

Dissolution enhancement of tadalafil by liquisolid technique

This study aimed to enhance the dissolution of tadalafil, a poorly water-soluble drug by applying liquisolid technique. The effects of two critical formulation variables, namely drug concentration (17.5% and 35%, w/w) and excipients ratio (10, 15 and 20) on dissolution rates were investigated. Pre-compression tests, including particle size distribution, flowability determination, Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM), were carried out to investigate the mechanism of dissolution enhancement. Tadalafil liquisolid tablets were prepared and their quality control tests, dissolution study, contact angle measurement, Raman mapping, and storage stability test were performed. The results suggested that all the liquisolid tablets exhibited significantly higher dissolution rates than the conventional tablets and pure tadalafil. FT-IR spectrum reflected no drug-excipient interactions. DSC and XRD studies indicated reduction in crystallinity of tadalafil, which was further confirmed by SEM and Raman mapping outcomes. The contact angle measurement demonstrated obvious increase in wetting property. Taken together, the reduction of particle size and crystallinity, and the improvement of wettability were the main mechanisms for the enhanced dissolution rate. No significant changes were observed in drug crystallinity and dissolution behavior after storage based on XRD, SEM and dissolution results.

The effect of surfactants on the dissolution behavior of amorphous formulations

The optimal design of oral amorphous formulations benefits from the use of excipients to maintain drug supersaturation and thus ensures adequate absorption during intestinal transit. The use of surfactants for the maintenance of supersaturation in amorphous formulations has not been investigated in detail. The main aim of this study was to investigate the effect of surfactant on the dissolution behavior of neat amorphous drug and binary polymer based solid dispersion. Indomethacin was used as the model drug and the surfactants studied were polysorbate 80 and poloxamer 407. The presence of surfactants (alone or in combination with polymers) in the buffer was detrimental to the dissolution of neat amorphous indomethacin, suggesting that the surfactants promoted the crystallization of neat amorphous indomethacin. In contrast, the presence of surfactants (0.01% w/v) in the buffer resulted in a significant improvement on the dissolution behavior of binary polymer based solid dispersion. Incorporating the surfactant to the formulation to form ternary solid dispersion adversely affected the dissolution behavior. In conclusion, the use of surfactants (as wetting or solubilization agents) in dissolution studies of neat amorphous drugs requires prudent consideration. The design of amorphous formulations with optimal dissolution performance requires the appropriate selection of a combination of excipients and consideration of the method of introducing the excipients.

Preparation of an oral acetaminophen film that is expected to improve medication administration: Effect of polyvinylpyrrolidone on physical properties of the film.

This study investigated the effect of polyvinylpyrrolidone (PVP) on a film containing carboxymethyl cellulose sodium (CMC) as a matrix to improve surface roughness caused by drug recrystallization. Acetaminophen (AA) was used as the model drug. Recrystallization is a problem encountered during the preparation of films that contain high drug doses, making them difficult to take. A film that does not disintegrate for clinical applications requires a smooth surface, moderate strength and elasticity, and a low level of adhesiveness to facilitate taking of the medication. Addition of PVP to the film formulation made the surface significantly smoother, and it was independent of the compounding method. Smooth films were obtained when the CMC concentration was kept constant and the amount of PVP was increased, but it also increased the adhesiveness and strength, and decreased the elasticity of the films. When high polymer concentration was kept constant and the ratio of CMC and PVP was varied, the films with smaller amounts of PVP tended to have a smoother surface and less adhesiveness. However, when the amount of PVP was reduced, the film strength increased and elasticity decreased. The amount of PVP had a negligible effect on drug dissolution behavior, making it useful for preparation of the AA film. However, it is necessary to determine the compounding method and the PVP load considering the adhesiveness, strength, and elasticity of the films.

Real-time UV imaging identifies the role of pH in insulin dissolution behavior in hydrogel-based subcutaneous tissue surrogate

For parenteral biopharmaceuticals, subcutaneous diffusion and, in the case of solid implants or suspensions, dissolution may govern the clinical profile of the drug product. Insight into the dissolution and diffusion processes of biopharmaceuticals after parenteral administration is fundamental in the development of new protein drug formulations. Using insulin as a model compound, the aim of this work was to develop a UV imaging-based method to study the real-time dissolution and diffusion behavior of solid protein drugs under stagnant conditions in a hydrogel matrix mimicking the subcutaneous tissue. Dissolution of proteins and peptides is a complex phenomenon as it may be coupled to the complicated acid base properties of these substances. UV imaging allowed the real-time dissolution and diffusion processes of insulin at different pH values and of different insulins to be studied. Dissolution rates were obtained, and the quantitative performance of the developed UV imaging method was verified. It was shown that the UV imaging dissolution method was able to differentiate between the behavior of different insulins and that human insulin dissolution was highly dependent on pH. pH effects in the microenvironment of the human insulin compacts at pH 7.40 and 3.00 were observed by UV–Vis imaging, explaining the different dissolution kinetics of human insulin at pH 7.40 and 3.00 as compared to pH 5.40. In conclusion, UV–Vis imaging may be a useful tool for studying dissolution, diffusion and pH effects in the vicinity of solid protein drug in a hydrogel matrix with the aim of achieving a better understanding of in vivo dissolution processes.