Cause of high variability in drug dissolution testing and its impact on setting tolerances

Releasing fast and slow: Non-destructive prediction of density and drug release from SLS 3D printed tablets using NIR spectroscopy

Selective laser sintering (SLS) 3D printing is a revolutionary 3D printing technology that has been found capable of creating drug products with varied release profiles by changing the laser scanning speed. Here, SLS 3D printed formulations (printlets) loaded with a narrow therapeutic index drug (theophylline) were produced using SLS 3D printing at varying laser scanning speeds (100-180 mm/s). The use of reflectance Fourier Transform - Near Infrared (FT-NIR) spectroscopy was evaluated as a non-destructive approach to predicting 3D printed tablet density and drug release at 2 h and 4 h. The printed drug products formulated with a higher laser speed exhibited an accelerated drug release and reduced density compared with the slower laser scanning speeds. Univariate calibration models were developed based on a baseline shift in the spectra in the third overtone region upon changing physical properties. For density prediction, the developed univariate model had high linearity (R² value = 0.9335) and accuracy (error < 0.029 mg/mm³). For drug release prediction at 2 h and 4 h, the developed univariate models demonstrated a linear correlation (R² values of 0.9383 and 0.9167, respectively) and accuracy (error < 4.4%). The predicted vs. actual dissolution profiles were found to be statistically similar (f₂ > 50) for all of the test printlets. Overall, this article demonstrates the feasibility of SLS 3D printing to produce drug products containing a narrow therapeutic index drug across a range of drug release profiles, as well as the potential for FT-NIR spectroscopy to predict the physical characteristics of SLS 3D printed drug products (drug release and density) as a non-destructive quality control method at the point-of-care.

Investigating the Influence of Tablet Location Inside Dissolution Test Apparatus on Polymer Erosion and Drug Release of a Surface-Erodible Sustained-Release Tablet Using Computational Simulation Methods

The objective of this work was to investigate the influence of tablet location along the bottom of a USP apparatus II vessel on polymer erosion and drug release of surface-erodible sustained-release tablets using computational simulation methods. Computational fluid dynamics (CFD) methods were performed to simulate the velocity distribution. A mathematical model was developed to describe polymer erosion and tablet deformation according to the mass transfer coefficient. Numerical analysis was used to simulate drug release controlled by drug diffusion and polymer erosion. The results indicated that tablets located at the off-center position deformed faster than the tablets located at the center position. However, tablet location had no profound impact on drug release rate since all drug release profiles were "similar" according to the f₂ similarity values which were above 50. Hence, our simulation supported that the USP apparatus II was a reliable and robust device for the dissolution testing of surface-erodible sustained-release tablets.

Vegetable oil-based hybrid microparticles as a green and biocompatible system for subcutaneous drug delivery

The aim of this study was to evidence the ability of vegetable oil-based hybrid microparticles (HMP) to be an efficient and safe drug delivery system after subcutaneous administration. The HMP resulted from combination of a thermostabilized emulsification process and a sol-gel chemistry. First of all, castor oil was successfully silylated by means of (3-Isocyanatopropyl)trimethoxysilane in solvent-free and catalyst-free conditions. Estradiol, as a model drug, was dissolved in silylated castor oil (ICOm) prior to emulsification, and then an optimal sol-gel crosslinking was achieved inside the ICOm microdroplets. The resulting estradiol-loaded microparticles were around 80 µm in size and allowed to entrap 4 wt% estradiol. Their release kinetics in a PBS/octanol biphasic system exhibited a one-week release profile, and the released estradiol was fully active on HeLa ERE-luciferase ERα cells. The hybrid microparticles were cytocompatible during preliminary tests on NIH 3T3 fibroblasts (ISO 10993-5 standard) and they were fully biocompatible after subcutaneous injection on mice (ISO 10993-6 standard) underlining their high potential as a safe and long-acting subcutaneous drug delivery system.

Availability of Guanitoxin in Water Samples Containing Sphaerospermopsis torques-reginae Cells Submitted to Dissolution Tests

Guanitoxin (GNT) is a potent neurotoxin produced by freshwater cyanobacteria that can cause the deaths of wild and domestic animals. Through reports of animal intoxication by cyanobacteria cells that produce GNT, this study aimed to investigate the bio-accessibility of GNT in simulated solutions of the gastrointestinal content in order to understand the process of toxicosis promoted by GNT in vivo. Dissolution tests were conducted with a mixture of Sphaerospermopsis torques-reginae (Cyanobacteria; Nostocales) cultures (30%) and gastrointestinal solutions with and without proteolytic enzymes (70%) at a temperature of 37 °C and rotation at 100 rpm for 2 h. The identification of GNT was performed by LC-QqQ-MS/MS through the transitions [M + H]⁺m/z 253 > 58 and [M + H]⁺m/z 253 > 159, which showed high concentrations of GNT in simulated gastric fluid solutions (p-value < 0.001) in comparison to simulated solutions of intestinal content. The gastric solution with pepsin promoted the stability of GNT (p-value < 0.05) compared to the simulated solution of gastric fluid at the same pH without the enzyme. However, the results showed that GNT is also available in intestinal fluids for a period of 2 h, and solutions containing the pancreatin enzyme influenced the bio-accessibility of the toxin more compared to the intestinal medium without enzyme (p-value < 0.05). Therefore, the bio-accessibility of the toxin must be considered both in the stomach and in the intestine, and may help in the diagnosis and prediction of exposure and risk in vivo through the oral ingestion of GNT-producing cyanobacteria cells.

Non-compendial vs compendial analytical tests - a powerful tool for predicting in vitro similarity of highly viscous oral suspension

In vitro dissolution profiles are increasingly used to evaluate drug release characteristics of pharmaceutical products. The dissolution methods is expected to be an appropriate tool for checking consistency of the pharmaceutical attributes by discriminating similarities and dissimilarities between different drug formulations. Expansion in development of novel “special” dosage forms, due to the manner in which these dosage forms release the active pharmaceutical ingredient, usually requires applying non-compendial dissolution strategy that differs from the traditional compendial recommendations. For demonstrating sameness in the dissolution profile, in vitro drug release comparison between test and reference product of highly viscous oral suspension by applying non-compendial peak vessel against conventional hemispheric vessel was demonstrated in this study. All reference batches exhibited high variability in dissolution data when using hemispheric vessel due to forming mound compact mass at the bottom of the vessel. Different strategies for samples manipulation, before and during dissolution period, were performed in order to eliminate additional variabilities. Modifications of conventional USP 2 apparatus such as using peak vessel provided with more reproducible and reliable result for distinguishing in vitro similarities between different formulations of oral suspensions. Misinterpretation of dissolution data can lead to negative impact on product development. Taking time to observe and evaluate what is happening to the product in the vessel during dissolution is of curtail consideration for proper selection of the dissolution strategy. Keywords: oral suspensions; in-vitro release; hydrodynamic variability; USP apparatus 2/ Paddle apparatus; peak vessel

Using Computational Fluid Dynamics to Compare Shear Rate and Turbulence in the TIM-Automated Gastric Compartment With USP Apparatus II

We use computational fluid dynamics to compare the shear rate and turbulence in an advanced in vitro gastric model (TIMagc) during its simulation of fasted state Migrating Motor Complex phases I and II, with the United States Pharmacopeia paddle dissolution apparatus II (USPII). A specific focus is placed on how shear rate in these apparatus affects erosion-based solid oral dosage forms. The study finds that tablet surface shear rates in TIMagc are strongly time dependant and fluctuate between 0.001 and 360 s^-1. In USPII, tablet surface shear rates are approximately constant for a given paddle speed and increase linearly from 9 s^-1 to 36 s^-1 as the paddle speed is increased from 25 to 100 rpm. A strong linear relationship is observed between tablet surface shear rate and tablet erosion rate in USPII, whereas TIMagc shows highly variable behavior. The flow regimes present in each apparatus are compared to in vivo predictions using Reynolds number analysis. Reynolds numbers for flow in TIMagc lie predominantly within the predicted in vivo bounds (0.01-30), whereas Reynolds numbers for flow in USPII lie above the predicted upper bound when operating with paddle speeds as low as 25 rpm (33).

Computational hydrodynamic comparison of a mini vessel and a USP 2 dissolution testing system to predict the dynamic operating conditions for similarity of dissolution performance

The hydrodynamic characteristics of a mini vessel and a USP 2 dissolution testing system were obtained and compared to predict the tablet-liquid mass transfer coefficient from velocity distributions near the tablet and establish the dynamic operating conditions under which dissolution in mini vessels could be conducted to generate concentration profiles similar to those in the USP 2. Velocity profiles were obtained experimentally using Particle Image Velocimetry (PIV). Computational Fluid Dynamics (CFD) was used to predict the velocity distribution and strain rate around a model tablet. A CFD-based mass transfer model was also developed. When plotted against strain rate, the predicted tablet-liquid mass transfer coefficient was found to be independent of the system where it was obtained, implying that a tablet would dissolve at the same rate in both systems provided that the concentration gradient between the tablet surface and the bulk is the same, the tablet surface area per unit liquid volume is identical, and the two systems are operated at the appropriate agitation speeds specified in this work. The results of this work will help dissolution scientists operate mini vessels so as to predict the dissolution profiles in the USP 2, especially during the early stages of drug development.

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.

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.

The Relationship Between the Evolution of an Internal Structure and Drug Dissolution from Controlled-Release Matrix Tablets

In the last decade, imaging has been introduced as a supplementary method to the dissolution tests, but a direct relationship of dissolution and imaging data has been almost completely overlooked. The purpose of this study was to assess the feasibility of relating magnetic resonance imaging (MRI) and dissolution data to elucidate dissolution profile features (i.e., kinetics, kinetics changes, and variability). Commercial, hydroxypropylmethyl cellulose-based quetiapine fumarate controlled-release matrix tablets were studied using the following two methods: (i) MRI inside the USP4 apparatus with subsequent machine learning-based image segmentation and (ii) dissolution testing with piecewise dissolution modeling. Obtained data were analyzed together using statistical data processing methods, including multiple linear regression. As a result, in this case, zeroth order release was found to be a consequence of internal structure evolution (interplay between region's areas-e.g., linear relationship between interface and core), which eventually resulted in core disappearance. Dry core disappearance had an impact on (i) changes in dissolution kinetics (from zeroth order to nonlinear) and (ii) an increase in variability of drug dissolution results. It can be concluded that it is feasible to parameterize changes in micro/meso morphology of hydrated, controlled release, swellable matrices using MRI to establish a causal relationship between the changes in morphology and drug dissolution. Presented results open new perspectives in practical application of combined MRI/dissolution to controlled-release drug products.

Enhanced recovery and dissolution of griseofulvin nanoparticles from surfactant-free nanocomposite microparticles incorporating wet-milled swellable dispersants

Nanocomposite microparticles (NCMPs) incorporating drug nanoparticles and wet-milled swellable dispersant particles were investigated as a surfactant-free drug delivery vehicle with the goal of enhancing the nanoparticle recovery and dissolution rate of poorly water-soluble drugs. Superdisintegrants were used as inexpensive, model, swellable dispersant particles by incorporating them into NCMP structure with or without wet-stirred media milling along with the drug. Suspensions of griseofulvin (GF, model drug) along with various dispersants produced by wet-milling were coated onto Pharmatose® to prepare NCMPs in a fluidized bed process. Hydroxypropyl cellulose (HPC, polymer) alone and with sodium dodecyl sulfate (SDS, surfactant) was used as base-line stabilizer/dispersant during milling. Croscarmellose sodium (CCS, superdisintegrant) and Mannitol were used as additional dispersants to prepare surfactant-free NCMPs. Nanoparticle recovery during redispersion and dissolution of the various GF-laden NCMPs were examined. Suspensions prepared by co-milling GF/HPC/CCS or milling GF/HPC/SDS were stable after 30 h of storage. After drying, due to its extensive swelling capacity, incorporation of wet-milled CCS in the NCMPs caused effective breakage of the NCMP structure and bursting of nanoparticle clusters, ultimately leading to fast recovery of the GF nanoparticles. Optimized wet co-milling and incorporation of CCS in NCMP structure led to superior dispersant performance over incorporation of unmilled CCS or physically mixed unmilled CCS with NCMPs. The enhanced redispersion correlated well with the fast GF dissolution from the NCMPs containing either CCS particles or SDS. Overall, swellable dispersant (CCS) particles, preferably in multimodal size distribution, enable a surfactant-free formulation for fast recovery/dissolution of the GF nanoparticles.

Preformulation studies of mucoadhesive tablets for carbamazepine sublingual administration

The purpose of this research work was the realization of a bi-layered mucoadhesive dosage form intended for carbamazepine sublingual administration and planned in order to obtain a unidirectional drug release and diffusion only across buccal mucosa avoiding the liberation in the buccal environment. Bi-layered tablets were constituted by an impermeable ethyl cellulose backing layer and a mucoadhesive layer. The latter was composed by a blend of a semisynthetic polymer, as hydroxyethyl cellulose or hydroxypropyl methylcellulose, and a synthetic polymer as, Carbopol(®), physically mixed in different ratios. The active ingredient carbamazepine was homogeneously dispersed in the mucoadhesive layer. The prepared formulations were carefully characterized by thickness, friability, swelling index, matrix erosion, ex vivo and in vivo mucoadhesive force and time, moreover patient acceptability was evaluated as well. Tablets constituted by Carbopol(®):hydroxypropyl methylcellulose (25%:75%) and Carbopol(®):hydroxyethyl cellulose (75%:25%) showed the best properties and for this reason were submitted to in vitro release studies. Both tablet groups gave good results in terms of ex vivo and in vivo bioadhesive force and time giving a sustained release.

A discriminatory intrinsic dissolution study using UV area imaging analysis to gain additional insights into the dissolution behaviour of active pharmaceutical ingredients

For efficient and effective drug development it is desirable to acquire a deep understanding of the dissolution behaviour of potential candidate drugs and their physical forms as early as possible and with the limited amounts of material that are available at that time. Using 3-10mg sample quantities, the ability of a UV imaging system is investigated to provide deep mechanistic insight into the intrinsic dissolution profiling of a range of compounds and physical forms assessed under flow conditions. Physical forms of indomethacin, theophylline and ibuprofen were compressed and their solid-state form confirmed before and after compression with X-ray methods and/or Raman spectroscopy. Intrinsic dissolution rates (IDRs) were determined using the compact's UV-imaging profile. The ratio in the IDRs for theophylline anhydrate over hydrate was 2.1 and the ratio for the alpha form of indomethacin over the gamma form was approximately 1.7. The discriminatory power of the novel UV area visualisation approach was shown to be high in that process-induced solid-state dissolution differences post-micronisation could be detected. Additionally, the scale-down system was able to visualise a previously observed increase in ibuprofen IDR with an increase in concentration of sodium dodecyl sulphate. The mechanistic dissolution insights from the visualisation approach are evident.

Transfer of drug dissolution testing by statistical approaches: Case study

The analytical transfer is a complete process that consists in transferring an analytical procedure from a sending laboratory to a receiving laboratory. After having experimentally demonstrated that also masters the procedure in order to avoid problems in the future. Method of transfers is now commonplace during the life cycle of analytical method in the pharmaceutical industry. No official guideline exists for a transfer methodology in pharmaceutical analysis and the regulatory word of transfer is more ambiguous than for validation. Therefore, in this study, Gauge repeatability and reproducibility (R&R) studies associated with other multivariate statistics appropriates were successfully applied for the transfer of the dissolution test of diclofenac sodium as a case study from a sending laboratory A (accredited laboratory) to a receiving laboratory B. The HPLC method for the determination of the percent release of diclofenac sodium in solid pharmaceutical forms (one is the discovered product and another generic) was validated using accuracy profile (total error) in the sender laboratory A. The results showed that the receiver laboratory B masters the test dissolution process, using the same HPLC analytical procedure developed in laboratory A. In conclusion, if the sender used the total error to validate its analytical method, dissolution test can be successfully transferred without mastering the analytical method validation by receiving laboratory B and the pharmaceutical analysis method state should be maintained to ensure the same reliable results in the receiving laboratory.

Vibration effects of lab equipment on dissolution testing with USP paddle method

Environmental vibration induced by laboratory equipment, building construction, or even by the analysts themselves is one of the more complicated factors affecting dissolution testing. It is difficult to control and/or calibrate by mechanical means or performance-based methods. In this study, dissolution apparatus vibration levels were measured in the frequency range from 10 to 270 Hz along all three axes using commercially available, single-axis accelerometers. The vibration distribution on the dissolution vessel plate was mapped, and acceleration was subsequently measured during dissolution runs involving NCDA#2 (10 mg prednisone) tablets using the paddle method. Several types of laboratory equipment were used to induce vibration during dissolution testing and vibration levels along the X-, Y-, and Z-axes of the vessel plate were measured in an attempt to establish possible correlation with dissolution results. In the frequency range studied, root mean square (RMS) acceleration values above 0.01 g, in either vertical or horizontal direction, typically affected dissolution results.

Impact of superdisintegrants on efavirenz release from tablet formulations

Efavirenz (EFV) tablets of different doses were prepared by a wet granulation process using different superdisintegrants such as crosscarmellose sodium (CCS), sodium starch glycollate (SSG) and crosspovidone (CP) to evaluate the role of different disintegrants on the in vitro release of EFV. Further, the mode of addition of disintegrants on EFV dissolution from tablets containing 600 mg of the drug was evaluated by incorporating the disintegrants extragranularly (EG), intragranularly (IG) or distributing them equally (IG and EG). In vitro dissolution of the prepared tablets was conducted using the recommended medium and a dissolution medium developed in-house, which had the ability to discriminate between the formulations. The t50 and t80 values were indicative of the fact that the drug release was faster from tablet formulations containing CP. CP was able to release the drug faster than the other two disintegrants in both dissolution media and the drug release was unaffected by the mode of CP addition.

Improved drug dissolution and product characterization using a crescent-shaped spindle

Drug release characteristics of two amoxicillin capsule products, 250 and 500 mg strength each, have been described using USP Paddle and crescent-shaped spindles. Using the same spindles, dissolution experiments were conducted with USP disintegrating (prednisone) and non-disintegrating (salicylic acid) calibrator tablets. Dissolution tests were conducted at 50 and 25 rev min−1 using USP Paddle and crescent-shaped spindles, respectively. In all cases, even with the higher 50 rev min−1, lower percent drug release results were observed with the Paddle spindle than with the crescent-shaped spindle, which was operated at 25 rev min−1. The observed lower dissolution for amoxicillin capsule products (&lt; 36 vs &gt; 87% at 30 min) and USP prednisone calibrator tablets (45.5 vs 99.8% at 30 min) with Paddle spindles appeared to occur because of the accumulation of the disintegrated material (cone formation) at the bottom, thus restricting product-medium interaction. Crescent-shaped spindles did not allow any accumulation of the product and provided improved interaction by mixing and stirring, and thus appeared to provide true drug dissolution characteristics of the products. On the other hand, in the case of non-disintegrating USP salicylic acid tablets (18.5 vs 24.4% at 30 min), lower results with Paddle spindles appeared to be because of stagnation of the tablets, which provided poor product-medium interaction for the surface touching the vessel surface. In this case, the crescent-shaped spindles moved the tablets at the base of the vessel, providing improved and efficient product-medium interaction, thus appearing to reflect truer dissolution characteristics of the tablets. The results highlight the possible artifacts of the USP Paddle spindle, which could lead to inaccurate characterization of drug release properties of test products. As reported previously, the artifacts of high variability in results and lack of relevance to product properties appeared to be related to poor mixing and variable hydrodynamics within a dissolution vessel. Results from this study provide further evidence that these artifacts might be addressed adequately using the crescent-shaped spindle, thus resulting in improved drug release as well as better product characterization.

Determination of intraluminal theophylline concentrations after oral intake of an immediate-and a slow-release dosage form

The purpose of this study was to evaluate a protocol which enables determining luminal drug concentrations after oral drug administration in man. Human intestinal fluids were aspirated from two sampling sites (duodenum and jejunum) at different time points after oral intake of theophylline; an immediate- and a slow-release dosage form were used to demonstrate the feasibility of discriminating between different formulations. Osmolarity and pH of the aspirates were measured and theophylline concentrations were determined by HPLC-UV. After intake of the immediate-release formulation of theophylline, duodenal maximum concentrations up to 3 mm were reached within 30 min. Theophylline appeared to be almost completely absorbed before it reached the second sampling site in the jejunum, as observed jejunal concentrations were lower than 10% of the maximal duodenal concentrations. These results are in agreement with fast dissolution and fast absorption through the intestinal mucosa, which could be expected as theophylline belongs to class I of the Biopharmaceutical Classification System. In contrast to the immediate-release formulation, administering the slow-release dosage form resulted in a gradual appearance of theophylline, reaching maximal intestinal concentrations below 300 μm. The proposed methodology can be used to assess luminal drug concentrations and to monitor the time- and site-dependent composition of intestinal fluids after intake of an oral dosage form. This approach may contribute to a better understanding of the behaviour of oral drug formulations in the gastrointestinal tract and may be exploited to further unravel the complexity of the gastrointestinal absorption process. In addition, knowledge of luminal drug concentrations may assist in the selection of drug concentrations applied in in-vitro permeability assays.

The random vibration effects on dissolution testing with USP apparatus 2

Dissolution testing is of primary importance for optimization of drug formulation and quality control, but test results typically show large variability. Vibration is one of the factors that can increase variability of dissolution testing. In this study, a Distek USP Apparatus 2 was used to perform dissolution testing using disintegrating 10 mg prednisone tablets at 50 rpm in 500 mL of 37 degrees C degassed water medium. A controllable vertical random vibration was applied to the dissolution apparatus during the dissolution testing. Real-time vibration waveforms were recorded using accelerometers placed at various locations on the vessel plate and on the dissolution vessels. Preliminary results showed a strong correlation between induced vibration and dissolution results. The vibration measured on the vessel plate correlates well with that measured within nearby vessels. The observed dissolution profiles suggest that vibration affects the disintegration and dissolving processes by different mechanisms, leading to high or low results depending upon during which phase of the dissolution process the vibration occurs. This study also presents a method capable of measuring vibration in a meaningful manner and how to determine where best to measure it.

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).

Vibration effects on dissolution tests with USP apparatuses 1 and 2

Dissolution testing is of primary importance for drug formulation and quality control. Many sources of variability are accounted for in the apparatus' mechanical calibration process; the effect of vibration on dissolution tests is not well understood in that the test's tolerance for environmental vibration with respect to magnitude or frequency is largely unknown. In this study, USP Apparatuses 1 and 2 were used. Dissolution profiles were obtained for both disintegrating and nondisintegrating tablets. In separate experiments, a lab vacuum pump or a lab mixer, both commonly used in laboratories, was used to generate vibration during dissolution runs with vibration parameters being recorded at a location close to the dissolution vessels. Disintegrating tablets were found to be sensitive to induced vibrations with both the paddle and basket methods. Average dissolution results for nondisintegrating tablets were not sensitive to the studied vibrations; however, variability of the results increased in some cases. The dissolution profiles suggest that the vibration effects on paddle and basket method occur through different mechanisms. The importance of vibration to dissolution test results depends on the vibration source, product being tested and the apparatus type.

Experimental and computational determination of blend time in USP Dissolution Testing Apparatus II

Blend time, the time to achieve a predefined level of homogeneity of a tracer in a mixing vessel, is an important parameter to evaluate the mixing efficiency of mixing devices. In this work, the blend time required to homogenize the liquid content of a USP Dissolution Testing Apparatus II under a number of operating conditions was obtained using two different experimental methods (tracer detection via colorimetric and conductivity measurements), a computational approach (computational fluid dynamics (CFD)), and a semi-theoretical analysis of the phenomenon. Under the standard geometric and operating conditions in which the USP Apparatus II is typically used (N = 50 rpm) the experimental blend time to achieve a 92.74% uniformity level was found to be between 27.5 and 33.3 s, depending on the location of the injection point and monitoring point for the tracer. These values were in close agreement with those obtained from CFD simulations. Changing the impeller vertical position (+/-2 mm) had only a limited effect. The CFD predictions also indicated that blend time is inversely proportional to the agitation speed. This conclusion is in agreement with previous reports and equations for blend time in mixing vessels. The blend times obtained in this work appear to be some two orders of magnitude smaller than the time usually required for appreciable tablet dissolution during the typical dissolution test, implying that the liquid contents of the USP Apparatus II can be considered to be relatively well mixed during the typical dissolution test.

Hydrodynamic Investigation of USP Dissolution Test Apparatus II

The USP Apparatus II is the device commonly used to conduct dissolution testing in the pharmaceutical industry. Despite its widespread use, dissolution testing remains susceptible to significant error and test failures, and limited information is available on the hydrodynamics of this apparatus. In this work, laser-Doppler velocimetry (LDV) and computational fluid dynamics (CFD) were used, respectively, to experimentally map and computationally predict the velocity distribution inside a standard USP Apparatus II under the typical operating conditions mandated by the dissolution test procedure. The flow in the apparatus is strongly dominated by the tangential component of the velocity. Secondary flows consist of an upper and lower recirculation loop in the vertical plane, above and below the impeller, respectively. A low recirculation zone was observed in the lower part of the hemispherical vessel bottom where the tablet dissolution process takes place. The radial and axial velocities in the region just below the impeller were found to be very small. This is the most critical region of the apparatus since the dissolving tablet will likely be at this location during the dissolution test. The velocities in this region change significantly over short distances along the vessel bottom. This implies that small variations in the location of the tablet on the vessel bottom caused by the randomness of the tablet descent through the liquid are likely to result in significantly different velocities and velocity gradients near the tablet. This is likely to introduce variability in the test.

Evaluation of the USP dissolution test method A for enteric-coated articles by planar laser-induced fluorescence

The USP drug release standard for delayed-release articles method A was evaluated using planar laser-induced fluorescence (PLIF). Prior authors have suggested that high pH "hot spots" could develop during the buffer medium addition of the method A enteric test. Additionally, previous studies have shown heterogeneous flow patterns and low-shear regions in the USP Apparatus II dissolution vessel, which may result in poor mixing of the buffer and acid media during the pH neutralization step of the method A enteric test. In this study, PLIF was used to evaluate the mixing patterns and evolution of pH neutralization during the buffer medium addition with rhodamine-B dye and the pH-sensitive dye fluorescein, respectively. Additionally, a comparison of the methods A and B enteric tests was performed with enteric-coated tablets containing rhodamine-B in the film so as to image the dissolution rate of the coating polymer with PLIF in order to determine if rapid buffer addition for the method A procedure accelerates the rate of film coat dissolution. Rapid addition of the 250 mL of buffer medium over 5 s to the 750 mL of acidic medium shows efficient mixing and pH neutralization due to the generation of large-scale stirring and enhanced turbulence resulting from the descending buffer medium. Slow addition near the paddle shaft over 5 min showed segregation in the recirculating region around the paddle shaft. In contrast, slow addition near the vessel wall introduces the medium into fluid outside of the recirculation region and enables transport over the entire vessel. Enteric-coated tablets tested according to method A with rapid medium addition and method B enteric tests performed identically, indicating no difference in polymer dissolution rate between the two tests. From the results of the PLIF imaging studies with rhodamine-B, fluorescein, and enteric-coated tablets, it was seen that "hot spots" affecting the dissolution performance of enteric dosage forms are not generated during the neutralization step of the method A enteric test namely when the media is added rapidly or outside of the recirculating region that surrounds the paddle shaft.

Towards a universal dissolution medium for carbamazepine

The aim of this study was to develop a dissolution medium for assessment of various carbamazepine (CBZ) formulations with different strengths. The design of a system inhibiting transformation of the anhydrous CBZ (CBZ A) to the dihydrate form (CBZ D), with minimum surface-active properties and suitable sink was investigated. The effect of pH, different concentrations of sodium lauryl sulphate (SLS), polyvinylpyrrolidone (PVP), and methyl cellulose (MC) on dissolution rate, solubility, dissolution solubility, and polymorphic transformation of CBZ was assessed. Solution-mediated transformation of CBZ A into CBZ D was monitored using optical microscopy, Fourier transform infrared spectroscopy and differential scanning calorimetry. Results showed that different strengths (100, 200, 400 mg) of the same CBZ tablet formulation exhibited different dissolution patterns, in 1% SLS (USP system). Such differences were reduced in 0.5% SLS solution which provided sufficient sink for up to 200 mg CBZ. It was also shown that solubility of CBZ A could not be detected in the media under study (water, SGF, SIF, and SLS solutions) due to its rapid transformation into CBZ D. The use of 3% PVP solution protected CBZ A from conversion for 75 min, while 0.01% MC completely inhibited the transformation up to 24 h. Therefore, a medium consisting of 0.5% SLS and 0.01% MC was selected. The medium provided: a) protection against transformation of CBZ A to CBZ D, b) increased solubility of CBZ A (204 mg % compared to 128 mg % of CBZ D in 0.5% SLS), c) suitable sink for up to 400 mg CBZ and d) overlapping dissolution profiles of various strengths of the same CBZ formulation. The suggested system may be a step in the way of solving CBZ dissolution problems that forced the USP to specify two similar dissolution tests with two different limits for conventional 200 mg CBZ tablets.

Shear-induced variability in the United States Pharmacopeia Apparatus 2: modifications to the existing system

The hydrodynamics within the United States Pharmacopeia Apparatus 2 have been shown to be highly non-uniform with a potential to yield substantial variability in dissolution rate measurements. Through the use of readily available engineering tools, several geometric modifications to the device were evaluated in this study. Specifically, we examined the influence of impeller clearance, agitator type (radial and axial), and vessel geometry (PEAK vessel) on the fluid flow properties and their relation to measured dissolution rates. Increasing the impeller clearance was observed to exacerbate the heterogeneity in shear and would likely result in greater variability in dissolution measurements. Altering the impeller type was shown to yield changes in the hydrodynamic behavior; however, the overall properties and problems with the test remain the same. Use of the PEAK vessel was observed to reduce shear heterogeneity in the regions where tablets are most likely to visit during testing; however, higher shear rates may result in the inability to discriminate between true differences in dissolution rates.

Hydrodynamics-induced variability in the USP apparatus II dissolution test

The USP tablet dissolution test is an analytical tool used for the verification of drug release processes and formulation selection within the pharmaceutical industry. Given the strong impact of this test, it is surprising that operating conditions and testing devices have been selected empirically. In fact, the flow phenomena in the USP test have received little attention in the past. An examination of the hydrodynamics in the USP apparatus II shows that the device is highly vulnerable to mixing problems that can affect testing performance and consistency. Experimental and computational techniques reveal that the flow field within the device is not uniform, and dissolution results can vary dramatically with the position of the tablet within the vessel. Specifically, computations predict sharp variations in the shear along the bottom of the vessel where the tablet is most likely to settle. Experiments in which the tablet location was carefully controlled reveal that the variation of shear within the testing device can affect the measured dissolution rate.

Shear distribution and variability in the USP Apparatus 2 under turbulent conditions

Computational analysis is used to examine the hydrodynamic environment within the USP Apparatus II at common operating conditions. Experimental validation of the computational model shows that the simulations of fluid motion match the dispersion of dye observed in experiments. The computations are then used to obtain data that cannot be easily measured with experiments, specifically the distribution of shear forces within the media and along the wall. Results show that the shear environment is highly non-uniform. Increasing the paddle speed from 50 to 100 rpm does not improve shear homogeneity within the apparatus. Experiments show that this uneven distribution of hydrodynamic forces is a direct cause of dissolution testing variability. This variability is large enough to cause for type II dissolution test failures, i.e., failures are a result of a vulnerability of the testing method rather than a problem with a dosage form. Future development of new dissolution tests should include evaluations of the hydrodynamic environments to eliminate this potential source of failure that is unrelated to product quality.

Choice of rotation speed (rpm) for bio-relevant drug dissolution testing using a crescent-shaped spindle

Recently a new crescent-shaped spindle has been proposed to address the issues related to poor hydrodynamics of the USP paddle apparatus and its associated artifacts of high variability and lack of bio-relevant results. For improved comparison of drug dissolution characterization, it is highly desirable to conduct testing using common experimental conditions such as spindle rotation speed. A study was conducted in which different products were tested using the crescent-shaped spindle to propose a common rpm speed for improved comparative drug dissolution testing. Conventional- (200 mg) and extended-release (200 and 400 mg) carbamazepine tablets of multiple brands and amoxicillin capsules (250 and 500 mg) were analysed using the crescent- shaped spindle at 25, 50 and/or 75 rpm. Drug release was evaluated for 1.5h for amoxicillin and for 3.0 and 24h for conventional- and extended-release carbamazepine tablets products respectively. The dissolution media used were 0.05 M phosphate buffer for amoxicillin capsules and water containing 0.5% sodium lauryl sulphate for carbamazepine tablet products. All products showed characteristic drug release profiles, reflecting the fast and slow drug release natures of the products tested with complete drug release within expected time durations. Based on an expected maximum drug release criterion of 85% in a reasonable time, at a relatively slow drug release rate and within a dosing interval, a spindle speed of 25 rpm was found to be the most appropriate. Thus, it is concluded that drug products can be analysed using a single spindle type (crescent) with a single rpm (25) which would, not only result in simpler dissolution procedures, but also provide enhanced efficiencies from economical and regulatory aspects.