Evaluation of hydrodynamics in the basket dissolution apparatus using computational fluid dynamics—Dissolution rate implications

Model-Informed Drug Development: In Silico Assessment of Drug Bioperformance following Oral and Percutaneous Administration

The pharmaceutical industry has faced significant changes in recent years, primarily influenced by regulatory standards, market competition, and the need to accelerate drug development. Model-informed drug development (MIDD) leverages quantitative computational models to facilitate decision-making processes. This approach sheds light on the complex interplay between the influence of a drug's performance and the resulting clinical outcomes. This comprehensive review aims to explain the mechanisms that control the dissolution and/or release of drugs and their subsequent permeation through biological membranes. Furthermore, the importance of simulating these processes through a variety of in silico models is emphasized. Advanced compartmental absorption models provide an analytical framework to understand the kinetics of transit, dissolution, and absorption associated with orally administered drugs. In contrast, for topical and transdermal drug delivery systems, the prediction of drug permeation is predominantly based on quantitative structure-permeation relationships and molecular dynamics simulations. This review describes a variety of modeling strategies, ranging from mechanistic to empirical equations, and highlights the growing importance of state-of-the-art tools such as artificial intelligence, as well as advanced imaging and spectroscopic techniques.

Particle Image Velocimetry (PIV) measurements of USP Apparatus 1 hydrodynamics with 500 mL fill volume

Changes to hydrodynamics arising from changes within dissolution testing systems, such as the fill volume level, can potentially cause variability in dissolution results. However, the literature on hydrodynamics in Apparatus 1 is quite limited and little information is available for vessels with different liquid volumes. Here, velocities in a USP Apparatus 1 vessel with a liquid fill volume of 500 mL, a common alternative to 900 mL, were experimentally measured using 2D-2C Particle Image Velocimetry (PIV) for different basket rotational speeds. Tangential velocities dominated the flow field, while axial and radial velocities were much lower and varied with location. The velocities distribution increased proportionately with the basket rotational speed almost everywhere in the vessel excepting for underneath the basket. A nearly horizontal radial liquid jet was found to originate close to the basket upper edge. Comparison of these results with those previously reported with 900-mL liquid volume (Sirasitthichoke et al., Intern. J. Pharmaceutics:X; 3 (2021) 100078) showed that the flow rate through the baskets was similar in both systems, implying that, at least initially, the amount of drug in solution would increase linearly with time. In other words, the flow rate through the baskets would be independent of the liquid volume. Velocity profiles were also found to be similar, except in the region above the basket, which was affected by the radial jet with an orientation significantly different between the 500-mL and the 900-mL systems.

Predictive Drug Release Modeling Across Dissolution Apparatuses I and II using Computational Fluid Dynamics

A modeling process is developed and validated with which active pharmaceutical ingredient (API) release is predicted across the United States Pharmacopeia (USP) dissolution apparatuses I and II based on limited experimental dissolution data (at minimum two dissolution profiles at different apparatus settings). The process accounts for formulation-specific drug release behavior and hydrodynamics in the apparatuses over the range of typical agitation rates and medium volumes. This modeling process involves measurement of experimental mass transfer coefficients via a conventional mass balance and the relationship of said mass transfer coefficients to hydrodynamics and apparatus setting via computational fluid dynamics (CFD). A novel 1-D model is hence established, which provided calibration data for a particular formulation, can model mass transfer coefficients and their corresponding drug release at apparatus configurations of interest. Based on validation against experimental data produced from five erosion-based formulations over a range of apparatus configurations, accuracy within 8 %LA (labelled amount of API) and an average root mean square deviation of 3 %LA is achieved. With this predictive capability, minimizing the number of dissolution experiments and the amount of chemical materials needed during method development appears feasible.

PhysioCell®; - a Novel, Bio-relevant Dissolution Apparatus: Hydrodynamic Conditions and Factors Influencing the Dissolution Dynamics

The physiologically relevant dissolution apparatuses simulate various aspects of gastrointestinal physiology and help to understand and predict the in vivo behavior of an oral dosage form. In this paper, we present and characterize for the first time a novel bio-relevant dissolution apparatus - PhysioCell®;. We evaluated the impact of several factors on the hydrodynamic conditions in the key vessel of the apparatus - the StressCell. We observed that the medium flow rate, but not the glass beads' size or amount, significantly influenced the dissolution rate. The relationship was disproportional: the increase in the flow rate from 4.6 to 9.0 mL/min reduced the dissolution time of 85% (T85) of the NaCl tablet by 46%, but from 134 to 300 mL/min decreased the T85 only by 24%. At the same time, the contractions of the StressCell's elastic walls promoted the content mixing and enhanced the dissolution rate of the paracetamol tablets: even very rare mixing contractions (1 per 10 min) decreased the T85 over twofold for the flow rate of 8 mL/min. In conclusion, the hydrodynamic conditions in the StressCell affect the dissolution of solid dosage forms and the understanding of these effects is crucial for modeling physiologically-based test conditions in the novel apparatus. Combinations of the unique PhysioCell®;features - adjustable medium flow, temperature control, controllable pH gradients and predefined mechanical agitation - can create a set of dissolution test scenarios for characterization of oral dosage forms and, in the future, making the in vitro-in vivo predictions. Graphical Abstract.

Simulating Tablet Dissolution Using Computational Fluid Dynamics and Experimental Modeling

The study of mass transfer is essential in the food digestion process, especially when gastric acid interacts with food and nutrients dissolve in the gastric system. In this study, a computational fluid dynamics (CFD) model was built based on an in vitro study, which investigated the mass transfer in a tablet dissolution process in a beaker and stirrer system. The predicted mass transfer coefficients from the simulation aligned well with the experimental values. The effect of the type and rotation speed of the stirrers was also investigated. Mass transfer from the tablet was found to be closely related to the tablet Reynolds number of the fluid (ranging from 0 to 938) and the shear stress (0 to 0.167 Pa) acting on the tablet. The relationship between the power number (0.0061 to 0.196) and the Reynolds number for the impeller (719 to 5715) was also derived for different stirrers.

The relative importance of internal and external physical resistances to mass transfer for caffeine release from apple pectin tablets

The relative importance of the physical resistances to mass transfer have been explored by using halved 13 mm diameter apple-pectin tablets containing caffeine, in different external stirring environments within a beaker containing simulated gastric fluid. The effects of different external (outside of the tablets) mass-transfer resistances to the tablets created through two different stirrer types and stirrer speeds, and different internal (inside of the tablets) mass-transfer resistances created through different tablet concentrations and thicknesses, have been studied. These studies enable internal diffusion coefficients of caffeine through the apple pectin matrix to be estimated, as well as estimating the external mass-transfer coefficients from benzoic acid dissolution, which are in the range of 6.5 × 10^-6 m/s – 2.4 × 10^-5 m/s for the 0.6 mm thick tablets and 4.0 × 10^-6 m/s – 1.6 × 10^-5 m/s for the 7 mm thick tablets. The diffusion coefficients for different caffeine concentrations in the apple pectin half-tablets have also been calculated in this study. The diffusivity of caffeine in the 7 mm half-tablets with 1% caffeine through 99% pectin was around (1.8 ± 0.5) × 10^-10 m²/s. This study points towards the development of multifilm mass-transfer theory for food digestion to create a more fundamentally based understanding of in-vitro digestion systems as an addition to the use of realistic in-vitro food digestion apparatus and give a better correlation between in-vitro and in-vivo digestion tests.

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Internal and external mass-transfer coefficients have been estimated.

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A caffeine-apple pectin system in simulated gastric solution has been used.

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The two-film mass-transfer theory has been used to estimate internal diffusion coefficients.

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Spray drying has been used to obtain caffeine and apple pectin powders.

Probing Differences in Mass-Transfer Coefficients in Beaker and Stirrer Digestion Systems and the USP Dissolution Apparatus 2 Using Benzoic Acid Tablets

Measurements of external mass-transfer coefficients for dissolution have been made with benzoic acid tablets with a diameter of 13 mm and approximately 3 mm thick, using two different dissolution systems. One system has been a beaker with a platform for the tablet and either 80 mL or 120 mL of water, with three different types of stirrers, and the other has been a USP dissolution apparatus 2 (paddle) with either 200 mL or 900 mL water. Various stirring speeds have also been used in the different pieces of equipment. The same mass-transfer coefficient may potentially be obtained from the same tablet by adjusting the operating conditions in the two different devices. The ranges of the external mass-transfer coefficients measured in both devices overlapped significantly, with the range being 0.193–4.48 × 10−5 m s−1 in the beaker and stirrer system and 0.222–3.45 × 10−5 m s−1 in the USP dissolution apparatus 2. Dimensional analysis of the results, using Sherwood and Reynolds numbers, shows that the Ranz–Marshall correlation provides a lower bound for estimates of the Sherwood numbers measured experimentally. Calculations of time constants for mass transfer suggest that mass transfer may be a rate-limiting step for dissolution and food digestion under some circumstances. The range of mass-transfer coefficients measured here is representative of other measurements from the literature, and the use of the Ranz–Marshall correlation supports the suggestion that this range of values should be generally expected in most situations.

Influence of basket mesh size on the hydrodynamics in the USP rotating basket dissolution testing Apparatus 1

The USP Apparatus 1 (rotating basket), typically used to assess drug product reproducibility and evaluate oral solid dosage forms performance, consists of a cylindrical glass vessel with a hemispherical bottom and a wire basket rotating at constant speed. Baskets with different wire openings can be used in alternative to the standard mesh opening (40-mesh) in order to discriminate between drug formulations during early stage of drug product development. Any changes introduced by different basket geometries can potentially and significantly impact the system hydrodynamics and cause variability of results, thus affecting product quality. In this work, Particle Image Velocimetry (PIV) was used to experimentally quantify the velocity distribution in the USP rotating basket Apparatus 1 using baskets of different mesh sizes (10-, 20-, and 40-mesh size) under the typical operating conditions described in dissolution testing procedures. Similar flow patterns were observed in all cases. However, the radial and axial velocities in the USP Apparatus 1 generally increased with increasingly larger openings of the basket mesh. Increasing the basket agitation speed also resulted in an overall increase in the velocities, especially below in the innermost core region below the basket, where drug fragments typically reside. More importantly, the flow entering and leaving the baskets was quantified from the velocity profiles in the immediate vicinity of the baskets. It was found that the flow increased significantly with increasingly larger mesh openings, which can, in turn, promote faster dissolution of the oral solid dosage forms, thus affecting drug dissolution profiles. Hence, the selection of the basket mesh size must be carefully considered during drug product development.

Determination of Intrinsic Drug Dissolution and Solute Effective Transport Rate during Laminar Fluid Flow at Different Velocities

The objective of this study was to determine the intrinsic drug dissolution rate (IDR) and the solute effective transport rate of some drugs, using a single particle dissolution technique, satisfying qualified dissolution conditions. The IDR of three poorly water-soluble compounds was measured in milli-Q water using four different fluid velocities. The enveloped surface area of the particles was calculated from the projected area and the perimeter of the particle observed in the microscope. Furthermore, computational fluid dynamics (CFD) simulations were used to theoretically investigate the flow conditions and dissolution rate, comparing box shaped particles and spherical particles with similar dimensions and surface area as the particles used the experiments. In this study, the IDR measurement of the single particles was determined within 5–60 min using particles with an initial projected area diameter (Dp) between 37.5–104.6 µm. The micropipette-assisted microscopy technique showed a good reproducibility between individual measurements, and the CFD simulations indicated a laminar flow around the particles at all flow velocities, even though there were evident differences in local particle dissolution rates. In conclusion, the IDR and solute effective transport rate were determined under well-defined fluid flow conditions. This type of approach can be used as a complementary approach to traditional dissolution studies to gain in-depth insights into the dissolution process of drug particles.

Experimental determination of the velocity distribution in USP Apparatus 1 (basket apparatus) using Particle Image Velocimetry (PIV)

The USP Apparatus 1 (basket apparatus) is commonly used to evaluate the dissolution performance of oral solid dosage forms. The hydrodynamics generated by the basket contributes, in general, to the dissolution rate and hence the dissolution results. Here, the hydrodynamics of Apparatus 1 was quantified in a vessel filled with 900-mL de-ionized water at room temperature by determining, via Particle Image Velocimetry (PIV), the velocity profiles on a vertical central plane and on 11 horizontal planes at different elevations at three different basket agitation speeds. The flow field was dominated by the tangential velocity component and was approximately symmetrical in all cases. Despite all precautions taken, small flow asymmetries were observed in the axial and radial directions. This appears to be an unavoidable characteristic of the flow in Apparatus 1. The magnitudes of the axial and radial velocity components varied with location but were always low. A small jet was seen emanating radially near the top edge of the basket. Velocities typically scaled well with increasing agitation speed in most regions of the vessel except for a region directly below the basket. The results of this work provide a major insight into the flow field inside the USP Apparatus 1.

Effects of porosity on drug release kinetics of swellable and erodible porous pharmaceutical solid dosage forms fabricated by hot melt droplet deposition 3D printing

3D printing has the unique ability to produce porous pharmaceutical solid dosage forms on-demand. Although using porosity to alter drug release kinetics has been proposed in the literature, the effects of porosity on the swellable and erodible porous solid dosage forms have not been explored. This study used a model formulation containing hypromellose acetate succinate (HPMCAS), polyethylene oxide (PEO) and paracetamol and a newly developed hot melt droplet deposition 3D printing method, Arburg plastic free-forming (APF), to examine the porosity effects on in vitro drug release. This is the first study reporting the use of APF on 3D printing porous pharmaceutical tablets. With the unique pellet feeding mechanism of APF, it is important to explore its potential applications in pharmaceutical additive manufacturing. The pores were created by altering the infill percentages (%) of the APF printing between 20 and 100% to generate porous tablets. The printing quality of these porous tablets was examined. The APF printed formulation swelled in pH 1.2 HCl and eroded in pH 6.8 PBS. During the dissolution at pH 1.2, the swelling of the printing pathway led to the gradual decreases in the open pore area and complete closure of pores for the tablets with high infills. In pH 6.8 buffer media, the direct correlation between drug release rate and infills was observed for the tablets printed with infill at and less than 60%. The results revealed that drug release kinetics were controlled by the complex interplay of the porosity and dynamic changes of the tablets caused by swelling and erosion. It also implied the potential impact of fluid hydrodynamics on the in vitro data collection and interpretation of porous solids.

Influence of in vitro release methods on assessment of tobramycin ophthalmic ointments

The current investigation was carried out to identify appropriate parameters for measuring the in vitro release of tobramycin (TOB) ophthalmic ointments and to evaluate the feasibility of in vitro release testing methods to assess the product performance. Drug release was assessed using USP dissolution apparatus IV and a modified USP dissolution apparatus I with simulated tear solution (STS) as the dissolution medium. The study variables included temperature, membrane material, source and pore size. The results demonstrated a significant influence of the membrane source and pore size on the release of TOB from the ointments. A dissolution medium temperature of 40 °C was found to be appropriate for the release studies. Both of the apparatuses were able to discriminate between the release profiles of ointments with different physicochemical/rheological properties. Maximum release rate of TOB was observed in the first hour which followed a logarithmic time dependent release. The correlation between the release rates/amounts and yield stress of the ointments was observed in both the dissolution apparatuses. These results support a rational approach to guide the in vitro release testing of TOB ophthalmic ointments.

Enteric Hard Capsules for Targeting the Small Intestine: Positive Correlation between In Vitro Disintegration and Dissolution Times

In this study, the potential for correlation between disintegration and dissolution performance of enteric-coated (EC) dosage forms was investigated. Different enteric hard shell capsule formulations containing caffeine as model drug were tested for disintegration (in a compendial disintegration tester) and for dissolution in both USP type I (basket) and type II (paddle) apparatuses using different media. Overall, good correlations were obtained. This was observed for both the basket and the paddle apparatus, indicating that the use of disintegration testing as a surrogate for dissolution testing (allowed by International Conference on Harmonization (ICH) for immediate release dosage forms in case, in addition to other conditions, a correlation between disintegration and dissolution is proven) could be extended to include delayed release dosage forms.

The Evaluation of Valsartan Biopharmaceutics Properties

BACKGROUND

Solubility, intestinal permeability and dissolution are the main factors that govern the rate and extent of drugs absorption and are directly related to bioavailability. Biopharmaceutics Classification System (BCS) is an important tool which uses in vitro results for comparison with bioavailability in vivo (biowaiver). Valsartan is widely used in the treatment of hypertension and shows different BCS classification in the literature (BCS class II or III).

OBJECTIVE

This work proposes the study of valsartan biopharmaceutics properties and its BCS classification.

METHODS

High Performance Liquid Chromatography (HPLC) method was developed and validated to quantify the drug in buffers pH 1.2, 4.5 and 6.8 respectively. Valsartan solubility was determined in these three different media using shake flask method and intrinsic dissolution rate. Evaluation of dissolution profile from coated tablets was conducted.

RESULTS

The low solubility (pH 1.2 and 4.5) and high solubility (pH 6.8) were observed for both solubility methods. Permeability data reported from the literature showed that valsartan is a low permeability drug. Valsartan presented the rapid release profile only in pH 6.8.

CONCLUSION

We defined that valsartan is a class IV drug, in disagreement with what has been published so far. It is important to emphasize that the conditions considered here are indicated to define the biopharmaceutics classification by regulatory agencies.

A study of the impact of excipient shielding on initial drug release using UV imaging

Knowledge on the dissolution behaviour of a drug is critical for efficient and effective product development. As the drug has almost always to be formulated with excipients in the design of a dosage form, it is important to examine the implications of the choice of excipients on the dissolution of the drug, among others, especially in the case of an immediate release dosage form. The objective of this study was to explore the potential of using an ultraviolet (UV) imaging technique to examine the effect of drug-excipient ratio on the initial dissolution of the drug, when formulated with a hydrophilic, water insoluble excipient. A series of drug-excipient binary blends with different ratios were prepared and compacted into 2 mm compacts, and their dissolution profiles captured with a UV imager. Chemical imaging via Raman spectroscopy was also performed on the compacts to quantify the fraction of drug presented on the compact surface. At low drug concentrations, a suppression in drug dissolution was observed, but beyond a critical drug-excipient ratio, the concentration of the excipient no longer played a role in affecting drug dissolution rates. Drug particle size was found to affect the critical drug-excipient ratio required to negate the shielding effect exerted by the excipient, such that a higher proportion of drug was required. It is postulated that the excipient served as a physical barrier, as well as competitor for water required for wetting during initial dissolution, thereby causing a delay in the wetting and dissolution of the drug.

Characterization of the Hydrodynamics in a Miniaturized Dissolution Apparatus

The hydrodynamics of a miniaturized dissolution apparatus was characterized using computational fluid dynamics simulations and analyzed in relation to the biorelevance and robustness of measurements of drug dissolution and precipitation kinetics from supersaturated drug solutions. The effect of using 3 different agitator geometries operated at 50, 100, 150, and 200 rpm as well as different positioning of an UV probe in the vessel was systematically evaluated. The computational fluid dynamics simulations were validated using a particle streak velocimetry experiment. The results show that the choice of agitator geometry influences the hydrodynamics of the system and indicates that an off-center probe position may result in more robust measurements. Furthermore, the study shows that the agitator geometry has a significant effect on supersaturation studies due to differences in the hydrodynamic shear produced by the agitator.

Industry's View on Using Quality Control, Biorelevant, and Clinically Relevant Dissolution Tests for Pharmaceutical Development, Registration, and Commercialization

This article intends to summarize the current views of the IQ Consortium Dissolution Working Group, which comprises various industry companies, on the roles of dissolution testing throughout pharmaceutical product development, registration, commercialization, and beyond. Over the past 3 decades, dissolution testing has evolved from a routine and straightforward test as a component of end-product release into a comprehensive set of tools that the developer can deploy at various stages of the product life cycle. The definitions of commonly used dissolution approaches, how they relate to one another and how they may be applied in modern drug development, and life cycle management is described in this article. Specifically, this article discusses the purpose, advantages, and limitations of quality control, biorelevant, and clinically relevant dissolution methods.

Computational fluid dynamics (CFD) studies of a miniaturized dissolution system

Dissolution testing is an important tool that has applications ranging from fundamental studies of drug-release mechanisms to quality control of the final product. The rate of release of the drug from the delivery system is known to be affected by hydrodynamics. In this study we used computational fluid dynamics to simulate and investigate the hydrodynamics in a novel miniaturized dissolution method for parenteral formulations. The dissolution method is based on a rotating disc system and uses a rotating sample reservoir which is separated from the remaining dissolution medium by a nylon screen. Sample reservoirs of two sizes were investigated (SR6 and SR8) and the hydrodynamic studies were performed at rotation rates of 100, 200 and 400rpm. The overall fluid flow was similar for all investigated cases, with a lateral upward spiraling motion and central downward motion in the form of a vortex to and through the screen. The simulations indicated that the exchange of dissolution medium between the sample reservoir and the remaining release medium was rapid for typical screens, for which almost complete mixing would be expected to occur within less than one minute at 400rpm. The local hydrodynamic conditions in the sample reservoirs depended on their size; SR8 appeared to be relatively more affected than SR6 by the resistance to liquid flow resulting from the screen.

The effect of the nature of organic acids and the hydrodynamic conditions on the dissolution of Pb particles

Rapid stabilization of pH values while Pb dissolution by three organic acids continues to progress.

Understanding and predicting the impact of critical dissolution variables for nifedipine immediate release capsules by multivariate data analysis

In this study the selection of in vivo predictive in vitro dissolution experimental set-ups using a multivariate analysis approach, in line with the Quality by Design (QbD) principles, is explored. The dissolution variables selected using a design of experiments (DoE) were the dissolution apparatus [USP1 apparatus (basket) and USP2 apparatus (paddle)], the rotational speed of the basket/or paddle, the operator conditions (dissolution apparatus brand and operator), the volume, the pH, and the ethanol content of the dissolution medium. The dissolution profiles of two nifedipine capsules (poorly soluble compound), under conditions mimicking the intake of the capsules with i. water, ii. orange juice and iii. an alcoholic drink (orange juice and ethanol) were analysed using multiple linear regression (MLR). Optimised dissolution set-ups, generated based on the mathematical model obtained via MLR, were used to build predicted in vitro-in vivo correlations (IVIVC). IVIVC could be achieved using physiologically relevant in vitro conditions mimicking the intake of the capsules with an alcoholic drink (orange juice and ethanol). The multivariate analysis revealed that the concentration of ethanol used in the in vitro dissolution experiments (47% v/v) can be lowered to less than 20% v/v, reflecting recently found physiological conditions.

Computational Fluid Dynamics Simulation of Hydrodynamics and Stresses in the PhEur/USP Disintegration Tester Under Fed and Fasted Fluid Characteristics

Disintegration of oral solid dosage forms is a prerequisite for drug dissolution and absorption and is to a large extent dependent on the pressures and hydrodynamic conditions in the solution that the dosage form is exposed to. In this work, the hydrodynamics in the PhEur/USP disintegration tester were investigated using computational fluid dynamics (CFD). Particle image velocimetry was used to validate the CFD predictions. The CFD simulations were performed with different Newtonian and non-Newtonian fluids, representing fasted and fed states. The results indicate that the current design and operating conditions of the disintegration test device, given by the pharmacopoeias, are not reproducing the in vivo situation. This holds true for the hydrodynamics in the disintegration tester that generates Reynolds numbers dissimilar to the reported in vivo situation. Also, when using homogenized US FDA meal, representing the fed state, too high viscosities and relative pressures are generated. The forces acting on the dosage form are too small for all fluids compared to the in vivo situation. The lack of peristaltic contractions, which generate hydrodynamics and shear stress in vivo, might be the major drawback of the compendial device resulting in the observed differences between predicted and in vivo measured hydrodynamics.

Evaluation of the coat quality of sustained release pellets by individual pellet dissolution methodology

This study explored the application of 400-DS dissolution apparatus 7 for individual pellet dissolution methodology by a design of experiment approach and compared its capability with that of the USP dissolution apparatus 1 and 2 for differentiating the coat quality of sustained release pellets. Drug loaded pellets were prepared by extrusion-spheronization from powder blends comprising 50%, w/w metformin, 25%, w/w microcrystalline cellulose and 25%, w/w lactose, and then coated with ethyl cellulose to produce sustained release pellets with 8% and 10%, w/w coat weight gains. Various pellet properties were investigated, including cumulative drug release behaviours of ensemble and individual pellets. When USP dissolution apparatus 1 and 2 were used for drug release study of the sustained release pellets prepared, floating and clumping of pellets were observed and confounded the release profiles of the ensemble pellets. Hence, the release profiles obtained did not characterize the actual drug release from individual pellet and the applicability of USP dissolution apparatus 1 and 2 to evaluate the coat quality of sustained release pellets was limited. The cumulative release profile of individual pellet using the 400-DS dissolution apparatus 7 was found to be more precise at distinguishing differences in the applied coat quality. The dip speed and dip interval of the reciprocating holder were critical operational parameters of 400-DS dissolution apparatus 7 that affected the drug release rate of a sustained release pellet during the individual dissolution study. The individual dissolution methodology using the 400-DS dissolution apparatus 7 is a promising technique to evaluate the individual pellet coat quality without the influence of confounding factors such as pellet floating and clumping observed during drug release test with dissolution apparatus 1 and 2, as well as to facilitate the elucidation of the actual drug release mechanism conferred by the applied sustained release coat onto the pellets.

Keeping a critical eye on the science and the regulation of oral drug absorption: a review

This review starts with an introduction on the theoretical aspects of biopharmaceutics and developments in this field from mid-1950s to late 1970s. It critically addresses issues related to fundamental processes in oral drug absorption such as the complex interplay between drugs and the gastrointestinal system. Special emphasis is placed on drug dissolution and permeability phenomena as well as on the mathematical modeling of oral drug absorption. The review ends with regulatory aspects of oral drug absorption focusing on bioequivalence studies and the US Food and Drug Administration and European Medicines Agency guidelines dealing with Biopharmaceutics Classification System and Biopharmaceutic Drug Disposition Classification System.

A new approach to dissolution testing by UV imaging and finite element simulations

PURPOSE

Most dissolution testing systems rely on analyzing samples taken remotely from the dissolving sample surface at different time points with poor time resolution and therefore provide relatively unresolved temporally and spatially information on the dissolution process. In this study, a flexible numerical model was combined with a novel UV imaging system, allowing monitoring of the dissolution process with sub second time resolution.

METHODS

The dissolution process was monitored by both effluent collection and UV imaging of compacts of paracetamol. A finite element model (FEM) was used to characterize the UV imaging system.

RESULTS

A finite element model of the UV imaging system was successfully built. The dissolution of paracetamol was studied by UV imaging and by analysis of the effluent. The dissolution rates obtained from the collected effluent were in good agreement with the numerical model. The numerical model allowed an assessment of the ability of the UV imager to measure dissolution-time profiles. The simulation was able to extend the experimental results to conditions not easily obtained experimentally.

CONCLUSIONS

Combining FEM,experimental dissolution data and UV imaging provided experimental validation of the FEM model as well as a detailed description of the dissolution process.

Using USP I and USP IV for discriminating dissolution rates of nano- and microparticle-loaded pharmaceutical strip-films

Recent interest in the development of drug particle-laden strip-films suggests the need for establishing standard regulatory tests for their dissolution. In this work, we consider the dissolution testing of griseofulvin (GF) particles, a poorly water-soluble compound, incorporated into a strip-film dosage form. The basket apparatus (USP I) and the flow-through cell dissolution apparatus (USP IV) were employed using 0.54% sodium dodecyl sulfate as the dissolution medium as per USP standard. Different rotational speeds and dissolution volumes were tested for the basket method while different cell patterns/strip-film position and dissolution media flow rate were tested using the flow-through cell dissolution method. The USP I was not able to discriminate dissolution of GF particles with respect to particle size. On the other hand, in the USP IV, GF nanoparticles incorporated in strip-films exhibited enhancement in dissolution rates and dissolution extent compared with GF microparticles incorporated in strip-films. Within the range of patterns and flow rates used, the optimal discrimination behavior was obtained when the strip-film was layered between glass beads and a flow rate of 16 ml/min was used. These results demonstrate the superior discriminatory power of the USP IV and suggest that it could be employed as a testing device in the development of strip-films containing drug nanoparticles.

Biopharmaceutics classification and intestinal absorption study of apigenin

The aim of the study was to characterize the biopharmaceutics classification system (BCS) category of apigenin (AP) using intrinsic dissolution rate (IDR) and rat intestinal permeability, and to investigate the intestinal absorption mechanism of AP in rats. In the present investigation, equilibrium solubility and intrinsic dissolution rate (IDR) of AP were estimated in phosphate buffers. Effective intestinal permeability (P(eff)) of AP was determined using single-pass intestinal perfusion (SPIP) technique in four segments (duodenum, jejunum, ileum and colon) of rat intestine at three concentrations (10, 50 and 100 μg/ml). The aqueous solubility of AP in tested phosphate buffers was very poor with maximum solubility of 2.16 μg/ml at pH 7.5. The IDR of AP was very low with a value of 0.006 mg/min/cm(2). The minimum and maximum P(eff)s determined by SPIP were 0.198×10(-4) and 0.713×10(-4) cm/s at jejunum and duodenum site, respectively. In addition, the concentration-dependent permeability behavior was observed in the duodenum and jejunum, which suggested that AP was transported by both passive and active carrier-mediated saturable mechanism in these two intestinal segments. However, the observed concentration-independent permeability behavior in ileum and colon indicated primarily passive transport mechanism of absorption of AP in the last two intestinal segments. AP was classified as class II drug of the BCS due to its low solubility and high intestinal permeability. AP could be well absorbed in the whole intestine with the main absorption site at duodenum. The absorption of AP in four intestinal segments exhibited different transport mechanisms.

Monitoring lidocaine single-crystal dissolution by ultraviolet imaging

Dissolution critically affects the bioavailability of Biopharmaceutics Classification System class 2 compounds. When unexpected dissolution behaviour occurs, detailed studies using high information content technologies are warranted. In the present study, an evaluation of real-time ultraviolet (UV) imaging for conducting single-crystal dissolution studies was performed. Using lidocaine as a model compound, the aim was to develop a setup capable of monitoring and quantifying the dissolution of lidocaine into a phosphate buffer, pH 7.4, under stagnant conditions. A single crystal of lidocaine was placed in the quartz dissolution cell and UV imaging was performed at 254 nm. Spatially and temporally resolved mapping of lidocaine concentration during the dissolution process was achieved from the recorded images. UV imaging facilitated the monitoring of lidocaine concentrations in the dissolution media adjacent to the single crystals. The concentration maps revealed the effects of natural convection due to density gradients on the dissolution process of lidocaine. UV imaging has great potential for in vitro drug dissolution testing.

Small Volume Dissolution Testing as a Powerful Method during Pharmaceutical Development

Standard compendia dissolution apparatus are the first choice for development of new dissolution methods. Nevertheless, limitations coming from the amount of material available, analytical sensitivity, lack of discrimination or biorelevance may warrant the use of non compendial methods. In this regard, the use of small volume dissolution methods offers strong advantages. The present study aims primarily to evaluate the dissolution performance of various drug products having different release mechanisms, using commercially available small volume USP2 dissolution equipment.

The present series of tests indicate that the small volume dissolution is a useful tool for the characterization of immediate release drug product. Depending on the release mechanism, different speed factors are proposed to mimic common one liter vessel performance. In addition, by increasing the discriminating power of the dissolution method, it potentially improves know how about formulations and on typical events which are evaluated during pharmaceutical development such as ageing or scale–up. In this regard, small volume dissolution is a method of choice in case of screening for critical quality attributes of rapidly dissolving tablets, where it is often difficult to detect differences using standard working conditions.

The science of USP 1 and 2 dissolution: present challenges and future relevance

Since its inception, the dissolution test has come under increasing levels of scrutiny regarding its relevance, especially to the correlation of results to levels of drug in blood. The technique is discussed, limited to solid oral dosage forms, beginning with the scientific origins of the dissolution test, followed by a discussion of the roles of dissolution in product development, consistent batch manufacture (QC release), and stability testing. The ultimate role of dissolution testing, "to have the results correlated to in vivo results or in vivo in vitro correlation," is reviewed. The recent debate on mechanical calibration versus performance testing using USP calibrator tablets is presented, followed by a discussion of variability and hydrodynamics of USP Apparatus 1 and Apparatus 2. Finally, the future of dissolution testing is discussed in terms of new initiatives in the industry such as quality by design (QbD), process analytical technology (PAT), and design of experiments (DOE).

A century of dissolution research: from Noyes and Whitney to the biopharmaceutics classification system

Dissolution research started to develop about 100 years ago as a field of physical chemistry and since then important progress has been made. However, explicit interest in drug related dissolution has grown only since the realisation that dissolution is an important factor of drug bioavailability in the 1950s. This review attempts to account the most important developments in the field, from a historical point of view. It is structured in a chronological order, from the theoretical foundations of dissolution, developed in the first half of the 20th century, and the development of a relationship between dissolution and bioavailability in the 1950s, going to the more recent developments in the framework of the Biopharmaceutics Classification System (BCS). Research on relevant fields of pharmaceutical technology, like sustained release formulations, where drug dissolution plays an important role, is reviewed. The review concludes with the modern trends on drug dissolution research and their regulatory implications.