Typical variability in drug dissolution testing: study with USP and FDA calibrator tablets and a marketed drug (glibenclamide) product

Measuring dissolution profiles of single controlled-release drug pellets

Many solid-dose oral drug products are engineered to release their active ingredients into the body at a certain rate. Techniques for measuring the dissolution or degradation of a drug product in vitro play a crucial role in predicting how a drug product will perform in vivo. However, existing techniques are often labor-intensive, time-consuming, irreproducible, require specialized analytical equipment, and provide only “snapshots” of drug dissolution every few minutes. These limitations make it difficult for pharmaceutical companies to obtain full dissolution profiles for drug products in a variety of different conditions, as recommended by the US Food and Drug Administration. Additionally, for drug dosage forms containing multiple controlled-release pellets, particles, beads, granules, etc. in a single capsule or tablet, measurements of the dissolution of the entire multi-particle capsule or tablet are incapable of detecting pellet-to-pellet variations in controlled release behavior. In this work, we demonstrate a simple and fully-automated technique for obtaining dissolution profiles from single controlled-release pellets. We accomplished this by inverting the drug dissolution problem: instead of measuring the increase in the concentration of drug compounds in the solution during dissolution (as is commonly done), we monitor the decrease in the buoyant mass of the solid controlled-release pellet as it dissolves. We weigh single controlled-release pellets in fluid using a vibrating tube sensor, a piece of glass tubing bent into a tuning-fork shape and filled with any desired fluid. An electronic circuit keeps the glass tube vibrating at its resonance frequency, which is inversely proportional to the mass of the tube and its contents. When a pellet flows through the tube, the resonance frequency briefly changes by an amount that is inversely proportional to the buoyant mass of the pellet. By passing the pellet back-and-forth through the vibrating tube sensor, we can monitor its mass as it degrades or dissolves, with high temporal resolution (measurements every few seconds) and mass resolution (700 nanogram resolution). As a proof-of-concept, we used this technique to measure the single-pellet dissolution profiles of several commercial controlled-release proton pump inhibitors in simulated stomach and intestinal contents, as well as comparing name-brand and generic formulations of the same drug. In each case, vibrating tube sensor data revealed significantly different dissolution profiles for the different drugs, and in some cases our method also revealed differences between different pellets from the same drug product. By measuring any controlled-release pellets, particles, beads, or granules in any physiologically-relevant environment in a fully-automated fashion, this method can augment and potentially replace current dissolution tests and support product development and quality assurance in the pharmaceutical industry.

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).

Validation of Dissolution Testing with Biorelevant Media: An OrBiTo Study

Dissolution testing with biorelevant media has become widespread in the pharmaceutical industry as a means of better understanding how drugs and formulations behave in the gastrointestinal tract. Until now, however, there have been few attempts to gauge the reproducibility of results obtained with these methods. The aim of this study was to determine the interlaboratory reproducibility of biorelevant dissolution testing, using the paddle apparatus (USP 2). Thirteen industrial and three academic laboratories participated in this study. All laboratories were provided with standard protocols for running the tests: dissolution in FaSSGF to simulate release in the stomach, dissolution in a single intestinal medium, FaSSIF, to simulate release in the small intestine, and a "transfer" (two-stage) protocol to simulate the concentration profile when conditions are changed from the gastric to the intestinal environment. The test products chosen were commercially available ibuprofen tablets and zafirlukast tablets. The biorelevant dissolution tests showed a high degree of reproducibility among the participating laboratories, even though several different batches of the commercially available medium preparation powder were used. Likewise, results were almost identicalbetween the commercial biorelevant media and those produced in-house. Comparing results to previous ring studies, including those performed with USP calibrator tablets or commercially available pharmaceutical products in a single medium, the results for the biorelevant studies were highly reproducible on an interlaboratory basis. Interlaboratory reproducibility with the two-stage test was also acceptable, although the variability was somewhat greater than with the single medium tests. Biorelevant dissolution testing is highly reproducible among laboratories and can be relied upon for cross-laboratory comparisons.

Galenic approaches in troubleshooting of glibenclamide tablet adhesion in compression machine punches

This study aimed to examine the adhesion of glibenclamide 5 mg tablets to the tools of compression machines. This problem is not commonly reported in the literature, since it is considered as tacit knowledge. The starting point was the implementation of three technical alternatives: changing the parameters of compression, evaluating the humidity of the powder blend and the manufacturer of the lubricant magnesium stearate. The adhesion was directly related to the characteristics of magnesium stearate from different manufacturers, and the feasibility of evaluating powder flow characteristics by different techniques that are not routinely followed in various pharmaceutical companies. In vitro dissolution tests showed that the magnesium stearate manufacturer can influence on the dissolution profile of glibenclamide tablets. This study presented various aspects of tablet adhesion to compression machine punches. Troubleshooting approaches can be, most of times, conducted based on previous experience, or an experimental research needs to be implemented in order to have confident results.

Poly dimethyl diallyl ammonium coated CMK-5 for sustained oral drug release

A new oral sustained drug delivery system (DDS) involving a combination of inorganic mesoporous material (CMK-5) and organic polymer poly dimethyl diallyl ammonium (PDDA) was established to determine its general suitability for use with poorly water soluble drugs. Nimodipine, carvedilol and fenofibrate, three different drugs with acidic or alkaline properties, were selected as model drugs and loaded into carriers. The physicochemical properties of the drug carriers were systematically studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and nitrogen adsorption. The structural body changes of the composites in release medium, with or without additional salts, were also studied using particle sizing systems, nitrogen adsorption and zeta potential measurement in order to investigate the sustained release mechanism of the drugs. The results obtained showed that sustained release of drug from the designed DDS was mainly due to the blockage effect arising from the strong swelling of the coated polymers when in contact with release medium. Additional salts, when they reached a certain level, allowed a dramatic burst release. We believe that our designed sustained DDS provide a new option for water insoluble drugs and can be considered as fundamental for those more sophisticated DDS increasingly required in modern medical treatments.

Application of the combinative particle size reduction technology H 42 to produce fast dissolving glibenclamide tablets

Standard particle size reduction techniques such as high pressure homogenization or wet bead milling are frequently used in the production of nanosuspensions. The need for micronized starting material and long process times are their evident disadvantages. Combinative particle size reduction technologies have been developed to overcome the drawbacks of the standard techniques. The H 42 combinative technology consists of a drug pre-treatment by means of spray-drying followed by standard high pressure homogenization. In the present paper, spray-drying process parameters influencing the diminution effectiveness, such as drug and surfactant concentration, were systematically analyzed. Subsequently, the untreated and pre-treated drug powders were homogenized for 20 cycles at 1500 bar. For untreated, micronized glibenclamide, the particle size analysis revealed a mean particle size of 772 nm and volume-based size distribution values of 2.686 μm (d50%) and 14.423 μm (d90%). The use of pre-treated material (10:1 glibenclamide/docusate sodium salt ratio spray-dried as ethanolic solution) resulted in a mean particle size of 236 nm and volume-based size distribution values of 0.131 μm (d50%) and 0.285 μm (d90%). These results were markedly improved compared to the standard process. The nanosuspensions were further transferred into tablet formulations. Wet granulation, freeze-drying and spray-drying were investigated as downstream methods to produce dry intermediates. Regarding the dissolution rate, the rank order of the downstream processes was as follows: Spray-drying>freeze-drying>wet granulation. The best drug release (90% within 10 min) was obtained for tablets produced with spray-dried nanosuspension containing 2% mannitol as matrix former. In comparison, the tablets processed with micronized glibenclamide showed a drug release of only 26% after 10 min. The H 42 combinative technology could be successfully applied in the production of small drug nanocrystals. A nanosuspension transfer to tablets that maintained the fast dissolution properties of the drug nanocrystals was successfully achieved.

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 (< 36 vs > 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.

Hydrodynamic simulation (computational fluid dynamics) of asymmetrically positioned tablets in the paddle dissolution apparatus: impact on dissolution rate and variability

The aim of this work was to investigate the dissolution rate from both the curved and planar surfaces of cylindrical compacts of benzoic acid, which were placed centrally and non-centrally at the base of the vessel of the paddle dissolution apparatus. The effect of fixing the compacts to a particular position on the variability of dissolution results was also examined. In addition, computational fluid dynamics (CFD) was used to simulate fluid flow around compacts in the different positions in the vessel, and the relationship between the local hydrodynamics in the region of the compacts and the dissolution rate determined. The dissolution rate was found to increase from the centre position to the off-centre positions for each surface examined. There was a corresponding increase in maximum fluid velocities calculated from the CFD fluid flow simulations at a fixed distance from the compact. There was less variability in dissolution from compacts fixed to any of the positions compared with those that were not fixed. Fluid flow around compacts in different positions could be successfully modelled, and hydrodynamic variability examined, using CFD. The effect of asymmetric fluid flow was evident visually from the change in shape of the eroded compacts.

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).

Detecting and identifying the complexation of nimodipine with hydroxypropyl-beta-cyclodextrin present in tablets by Raman spectroscopy

For CD-based formulations, it is important to directly monitor the complexation status of the drug present in final dosage form pharmaceuticals. In this work, Raman spectroscopy was explored for the detection and identification of the Nimodipine/hydroxypropyl-beta-cyclodextrin (NMD/HPbetaCD) complexation present in the tablet. The evident, consistent Raman spectral changes in the shift, height ratio and area ratio for the characteristic bands of NMD molecule were featured in the NMD/HPbetaCD complex, and employed to distinguish between complexed and uncomplexed NMD in tablets. A number of practical issues for the Raman measurements performed on the tablets were considered and addressed. The Raman approach and dissolution test were applied to different tablets prepared experimentally at variable granulations. The results demonstrated that the Raman approach can serve as a promising methodology for tablet identification on the complexation. Wet granulation facilitated the process-induced transformations in the complexation. The adequate ethanol in the granulating fluid appeared optimized for the complexation of the two components. The spectral characteristics for dissociation in the tablets were in full accordance with the observations of their diminished initial dissolution parameters. It implied the possibility that the tablet dissolution can be predicted from the Raman interpretation.

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.

Effects of Deaeration Methods on Dissolution Testing in Aqueous Media: A Study Using a Total Dissolved Gas Pressure Meter**Opinions expressed in this report are those of the authors and do not necessarily reflect the views or policies of the FDA

Dissolution testing is a critical method for the determination of pharmaceutical product quality and bioequivalence. For some products, dissolved gases in the dissolution medium affect dissolution results thus requiring degassing of the medium prior to use. In this study, we use a total dissolved gas and oxygen meter to measure both oxygen and total gases in dissolution media before and after application of a variety of deaeration methods. Dissolution testing results using a 10 mg Prednisone tablet (NCDA #2) are compared with the percent saturation of oxygen and total gases found in the medium. Reaeration of the medium during different stirring rates was also measured. This study confirms that measurement of total gases and not just oxygen in the medium is necessary to assess adequacy for dissolution testing. For those deaeration techniques that are performed at room temperature, the percent saturation of the total dissolved gases must be well below 100% to prevent outgassing once medium is brought to dissolution test method temperature, typically 37 degrees C.

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.

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.

In Vitro and In Vivo Evaluation of Glibenclamide in Solid Dispersion Systems

The purpose of this work is to improve the dissolution and bioavailability characteristics of glibenclamide as compared to Daonil tablets (Hoechst). Solid dispersions of glibenclamide in Gelucire 44/14 (Formula 1) and in polyethylene glycol 6000 (PEG 6000) (Formula 2) were prepared by fusion method. In vitro dissolution studies showed that the dispersing systems containing glibenclamide and Gelucire 44/ 14 or PEG 6000 gave faster dissolution rates than the reference product Daonil. The in vivo bioavailability study was assessed in six healthy male volunteers in crossover design with a 1-week washout period. Both formulas were found to be significantly different from Daonil with regard to the extent of absorption as indicated by the area under serum concentration-time curve. Both formulas are not significantly different from Daonil with respect to time of peak plasma concentration Tmax. It is concluded from this pilot study that the ranking of the in vitro dissolution is similar to the ranking of in vivo availability. The ranking of the three preparations in term of dissolution rate and extent of absorption is as follows: Formula 2>Formula 1 >Daonil.

Computational fluid dynamics modeling of the paddle dissolution apparatus: agitation rate, mixing patterns, and fluid velocities

The purpose of this research was to further investigate the hydrodynamics of the United States Pharmacopeia (USP) paddle dissolution apparatus using a previously generated computational fluid dynamics (CFD) model. The influence of paddle rotational speed on the hydrodynamics in the dissolution vessel was simulated. The maximum velocity magnitude for axial and tangential velocities at different locations in the vessel was found to increase linearly with the paddle rotational speed. Path-lines of fluid mixing, which were examined from a central region at the base of the vessel, did not reveal a region of poor mixing between the upper cylindrical and lower hemispherical volumes, as previously speculated. Considerable differences in the resulting flow patterns were observed for paddle rotational speeds between 25 and 150 rpm. The approximate time required to achieve complete mixing varied between 2 to 5 seconds at 150 rpm and 40 to 60 seconds at 25 rpm, although complete mixing was achievable for each speed examined. An analysis of CFD-generated velocities above the top surface of a cylindrical compact positioned at the base of the vessel, below the center of the rotating paddle, revealed that the fluid in this region was undergoing solid body rotation. An examination of the velocity boundary layers adjacent to the curved surface of the compact revealed large peaks in the shear rates for a region within ~3 mm from the base of the compact, consistent with a "grooving" effect, which had been previously seen on the surface of compacts following dissolution, associated with a higher dissolution rate in this region.

Development of a dissolution medium for nimodipine tablets based on bioavailability evaluation

A marked difference in the dissolution rate between two brands of nimodipine tablets was observed using a newly developed dissolution medium of pH 4.5 acetate buffer containing 0.05% sodium dodecyl sulfate (SDS). However, when pH 4.5 acetate buffer containing 0.3% SDS was used as dissolution medium, which was specified in the edition, the dissolution results of the both brands conformed to the BP requirements and no significant difference in dissolution was observed. The dissolution data obtained for two commercial brands of nimodipine tablets indicate the superiority of the proposed system as a discriminatory dissolution medium for nimodipine tablets. The relative bioavailability of the two brands of nimodipine tablets was determined in healthy adult volunteers after a single dose in a randomized crossover study. Plasma concentrations were determined by a liquid chromatography-tandem mass spectrometry method. Statistical comparison of the AUC(0-T), AUC(0- infinity), C(max), and T(max) indicated a significant difference in the two brands of nimodipine tablets.

Applications of a new device (spindle) for improved characterization of drug release (dissolution) of pharmaceutical products

A crescent spindle (patent pending) is described which may be used in place of the USP paddle component in USP dissolution apparatus 2. The new spindle is curve shaped, corresponding to the bottom of a dissolution vessel, with attached bristles to fill in the gap between the spindle and the surface of the vessel. The geometry of the new spindle provides more efficient mixing than the USP paddle and prevents accumulation of disintegrated material (no cone formation). Using the new spindle, in comparison with the USP paddle, dissolution characteristics of three drug products: 250 mg amoxicillin capsules, 15.6 g acetylsalicylic acid (ASA) boluses and 200 mg carbamzepine tablets were evaluated. The experimental conditions for dissolution testing with the two stirring devices included; 900 ml of 0.05 M phosphate buffer, pH 6.8 with 50 rpm, 900 ml of 0.05 M acetate buffer, pH 4.5-ethanol (7:3) with 50 rpm, and water containing 1% sodium lauryl sulphate with 75 rpm for amoxicillin capsules, ASA boluses and carbamazepine tablets, respectively. Uncharacteristic of the test products, which are fast release, the USP paddle provides significantly slower drug release. For example, 90 min for <80% drug release vs. 10 min for >90% for amoxicillin capsules and 6 h for 80% vs. 30 min for >90% for ASA boluses with USP paddle vs. the new spindle. In case of the carbamazepine tablets, three products which are bioequivalent and prescribed interchangeably, the USP paddle method shows significantly different dissolution characteristics. However, with the new device, all these products show similar drug release characteristics, a better reflection of product release characteristics and in vivo drug release behaviour. Compared with the USP paddle, the suggested device (spindle) provides improved stirring and mixing which appears to provide more appropriate (biorelevant) characterization of pharmaceutical products.

Optimization of dissolution test precision for a ketoprofen oral extended-release product

An example of application of experimental design methodologies to the set up of dissolution test conditions for a new ketoprofen oral extended-release dosage form is presented. The aim of the work was to find the best experimental conditions, using a USP apparatus 2 (paddle), for maximizing the method precision as degree of repeatability. The considered factors mainly influencing the dissolution test results were pH and volume of dissolution medium, and paddle stirring speed. Two distinct 4-run Plackett-Burman designs were carried out: one at gastric and the other at intestinal pH values. Each run was performed in triplicate in order to calculate the standard deviations of the drug dissolution efficiency at 60 and 120 min, selected as responses to be minimized. Optimum conditions to carry out the dissolution test were: 900 ml volume of dissolution medium and 70 rpm paddle stirring speed for both environments and pH 1 and 5.5, for the gastric and intestinal environment, respectively.

Dissolution of USP prednisone calibrator tablets: effects of stirring conditions and particle size distribution

We investigate the effect of stirring conditions on the dissolution of United States Pharmacopoeial Convention (USP) prednisone calibrator tablets. The experiments are performed in an automated USP-II dissolution test apparatus. For this study we use a special paddle-propeller, which can be changed from an ordinary paddle to either a pulling or pushing propeller by changing the angle of the paddle blades. According to the dissolution curves obtained we find that the fastest dissolution, and hence best stirring at a certain stirring frequency, is obtained when the blades of the paddle-propeller is about +30 degrees. This setting corresponds to a pushing, downward flow in the centre of the vessel. We show that the shape of the dissolution curves is similar to that expected from a mix of two different fractions of particles, provided that the stirring is sufficiently intense: one fraction, approximately 60 wt.%, with small particles, and one fraction with large particles. The weight of a large particle is about 100-250 times that of a small. We derive a mathematical expression, based on the cube root law, for the dissolution curves. The expression is fitted to the experimental dissolution curves to investigate the variation of key parameters with stirring and temperature.

Simulating the hydrodynamic conditions in the United States Pharmacopeia paddle dissolution apparatus

The objective of this work was to examine the feasibility of developing a high-performance computing software system to simulate the United States Pharmacopeia (USP) dissolution apparatus 2 (paddle apparatus) and thus aid in characterizing the fluid hydrodynamics in the method. The USP apparatus was modeled using the hydrodynamic package Fluent. The Gambit program was used to create a "wireframe" of the apparatus and generate the 3-dimensional grids for the computational fluid dynamics solver. The Fluent solver was run on an IBM RS/6000 SP distributed memory parallel processor system, using 8 processors. Configurations with and without a tablet present were developed and examined. Simulations for a liquid-filled vessel at a paddle speed of 50 rpm were generated. Large variations in fluid velocity magnitudes with position in the vessel were evident. Fluid velocity predictions were in good agreement with those previously published, using laser Doppler velocity measurements. A low-velocity domain was evident directly below the center of the rotating paddle. The model was extended to simulate the impact of the presence of a cylindrical tablet in the base of the dissolution vessel. The presence of the tablet complicated the local fluid flow, and large fluid shear rates were evident at the base of the compact. Fluid shear rates varied depending on the tablet surface and the location on the surface and were consistent with the reported asymmetrical dissolution of model tablets. The approach has the potential to explain the variable dissolution results reported and to aid in the design/prediction of optimal dissolution conditions for in vitro--in vivo correlations.

Accelerated dissolution testing for improved quality assurance

In pharmaceutical production of controlled release tablets and capsules, a rapid and automated at-line dissolution test for quality assurance of semi-products is advantageous. For effective control of the production, the analysis should not take more than about an hour, without loss of correlation to the ordinary (USP) dissolution test of the final product. For almost a decade, the ACDRA apparatus (ACcelerated Dissolution Rate Analysis) have been used for this purpose at AstraZeneca Tablet Production Sweden (TPS). In this paper, we give examples on different ways to accelerate the dissolution process. We use the USP dissolution calibrator tablets of salicylic acid (non-disintegrating type) to illustrate the strategy. We investigate the accelerated dissolution of the dissolution calibrator tablets, and show how it can be correlated with the dissolution in the ordinary USP-II equipment. The dissolution process was accelerated by variation of temperature, solvent and stirring. For example, we show that by increasing the temperature to 70 degrees C, changing the solvent to water, and increasing the stirring, it is possible to accelerate the dissolution by a factor of 5, without any loss of correlation to the dissolution process in the ordinary test.

Typical variability and evaluation of sources of variability in drug dissolution testing

To investigate variability in dissolution testing an international collaborative study was performed by 29 laboratories. Glibenclamide (glyburide) tablets were used in the investigation in which multipoint dissolution profiles were established using USP paddle apparatus. In contrast to a previous report, the variability of the glibenclamide dissolution data was significantly lower. Total variances (s(2)) were found to range from 18.34-44.18, Between Laboratory and Between Analyst variances (synthetic value) ranged from 12.9-38.7 and the Within Analyst variances ranged from 5.08-5.78. The dissolution profiles and corresponding variances obtained by laboratories with little or no experience in glibenclamide dissolution testing were similar to those obtained by more experienced laboratories, indicating that the test, especially when designed as multiple point dissolution testing, is sufficiently robust and capable of identifying differences in a manufacturing process or drug formulation. The smallest statistically detectable mean difference between two dissolution runs was calculated (95% CI) to be 7% for one analyst, or 5% if two analysts were to perform the dissolution tests.

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

Considering a variable mixing/stirring and flow pattern in a drug dissolution vessel as a likely source of high variability in results, experiments were conducted using USP paddle apparatus by placing (aligned to the walls) a metal strip (1.7 mm thickx6.4 mm wide) in a dissolution vessel. The metal strip forces the undisintegrated tablet to settle about 3 mm away from the centre, facilitates spread of disintegrated material and diminishes the cone formation at the bottom of the vessel. To assess the impact of this altered environment in the vessel, but still maintaining the vessel dimensions within required specifications, drug release characteristics were evaluated for products having different formulation/manufacturing attributes. Tests were conducted with calibrator tablets (USP prednisone and salicylic acid tablets and FDA proposed NCDA No. 2 prednisone tablets) and two commercially available products (250 mg amoxicillin capsules and 5 mg glibenclamide tablets). Except for the glibenclamide tablet product, all products gave significantly (P<0.01) higher dissolution results with vessels containing metal strip than without. The extent of increased dissolution with the metal strip varied from product to product i.e. USP prednisone tablet was the smallest (14.4%) and NCDA No. 2 was the largest (88.4%). Based on the results obtained from this study, it is concluded that employing the current apparatuses, in many cases products will provide lower than anticipated results which may not be reflective of the product drug release characteristics. Test-to-test variability, within or between laboratories, can also be very high depending on the settling position of the product once dropped in the vessel and/or due to slight aberration in the walls of the vessel by altering the extent of spread of disintegrated material at the bottom of the vessel. Thus, dissolution testing will require wider tolerances to be useful for comparison of batch-to-batch or interlaboratory results.