The effect of compression force on surface structure, crushing strength, friability and disintegration time of erythromycin acistrate tablets

Non-destructive Detection of Disintegrant Levels in Compressed Oral Solid Dosage Forms

Quality issues related to compressed oral solid dosage (OSD) forms, such as tablets, arise during the design, development, and production stages, despite established processes and robust production tools. One of the primary quality concerns is the disintegration properties and drug release profile of immediate-release OSD products, which depend on their micro-texture and micro-viscoelastic properties at the grain level. These properties are influenced by the composition of the formulation, particularly the disintegrant level in the tablet matrix and the porosity of the matrix. In this study, a novel, rapid, non-destructive ultrasonic characterization technique was proposed to correlate the sensitivity of propagating elastic wave speeds, physical/mechanical properties, and the dispersion profile of the OSD material with the disintegrant level (% w/w) in the formulation and the compression force applied during tableting. The proposed characterization framework involves transmitting pressure (longitudinal) and shear (transverse) waves through the OSDs to calculate the speed of sound, which in turn provides information on the apparent Young's and shear moduli. In addition, the attenuation profile of the propagating wave is obtained through dispersion analysis. To investigate the impact of disintegrants and compression force on ultrasonic wave propagation in OSDs, we incorporated seven levels of a frequently used disintegrant. In each formulation, OSDs are compacted in five compaction forces. The sensitivity of wave speeds, physical/mechanical properties, and attenuation profile was observed with each disintegrant and compression force level. The utilization of ultrasonic techniques may present a viable solution for rapid, non-destructive, non-invasive, and cost-effective testing methods required in continuous manufacturing (CM) and real-time release testing (RTRT), and its practical utility in pharmaceutical manufacturing is also discussed.

Combining Liquisolid and Co-grinding Techniques to Enhance the Dissolution Rate of Celecoxib

Purpose

The classic liquisolid technique is used to enhance the dissolution rate of poorly water-soluble drugs, but in some cases, it is impossible to reach the desired dissolution rate using this technique alone. Therefore, a novel approach using a combination of ball milling and liquisolid technology was investigated to improve the dissolution rate for celecoxib.

Methods

First, celecoxib was dispersed in a liquid vehicle (PEG 200), then ground in a ball mill for 3 h. Other excipients, including PVP, microcrystalline cellulose as the carrier powder, and silica as the coating material, were added to the mortar. Dissolution testing was carried out in simulated intestinal fluid (SIF) and simulated gastric fluid (SGF) media. The effects of aging on the hardness and dissolution profile were also studied. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) was used to identify changes in the crystallinity or complex formation.

Results

The novel formulations showed a higher dissolution rate than the conventional tablet or classic liquisolid formulations. Aging did not affect the hardness and dissolution profiles of the liquisolid compacts. The DSC and XRD results suggested that the enhanced dissolution rate is not caused by the formation of any complexes and reduction in crystallinity degree may contribute to the dissolution enhancement. The enhanced dissolution rate is attributed to the elevated specific surface area of the drug in the liquisolid state.

Conclusion

The results showed that liquisolid technology combined with ball milling is an efficient tool for enhancing the dissolution of poorly water-soluble drugs.

Use of Atomic Force Microscopy (AFM) to monitor surface crystallization in caffeine-oxalic acid (CAFOXA) cocrystal compacts

Our objective was to monitor the surface crystallization in disordered caffeine-oxalic acid (CAFOXA) cocrystals following exposure to elevated water vapor pressure. This was accomplished using atomic force microscopy (AFM). Disorder was induced in the cocrystal particles by the common pharmaceutical unit operations of milling and compaction. The 'activated' solid, upon exposure to elevated water vapor pressure, had a high propensity to sorb water. This led to a rise in molecular mobility and the surface underwent rapid crystallization to form needle shaped crystals of CAFOXA. Using AFM height and phase imaging, we were able to directly visualize phase transformations on the compact surface. The milled compacts exhibited higher processing induced disorder than the unmilled compacts, thereby accelerating the surface recrystallization.

Process Analytical Technology Tools for Monitoring Pharmaceutical Unit Operations: A Control Strategy for Continuous Process Verification

Various frameworks and methods, such as quality by design (QbD), real time release test (RTRT), and continuous process verification (CPV), have been introduced to improve drug product quality in the pharmaceutical industry. The methods recognize that an appropriate combination of process controls and predefined material attributes and intermediate quality attributes (IQAs) during processing may provide greater assurance of product quality than end-product testing. The efficient analysis method to monitor the relationship between process and quality should be used. Process analytical technology (PAT) was introduced to analyze IQAs during the process of establishing regulatory specifications and facilitating continuous manufacturing improvement. Although PAT was introduced in the pharmaceutical industry in the early 21st century, new PAT tools have been introduced during the last 20 years. In this review, we present the recent pharmaceutical PAT tools and their application in pharmaceutical unit operations. Based on unit operations, the significant IQAs monitored by PAT are presented to establish a control strategy for CPV and real time release testing (RTRT). In addition, the equipment type used in unit operation, PAT tools, multivariate statistical tools, and mathematical preprocessing are introduced, along with relevant literature. This review suggests that various PAT tools are rapidly advancing, and various IQAs are efficiently and precisely monitored in the pharmaceutical industry. Therefore, PAT could be a fundamental tool for the present QbD and CPV to improve drug product quality.

Benefits of Fractal Approaches in Solid Dosage Form Development

Pharmaceutical formulations are complex systems consisting of active pharmaceutical ingredient(s) and a number of excipients selected to provide the intended performance of the product. The understanding of materials' properties and technological processes is a requirement for building quality into pharmaceutical products. Such understanding is gained mostly from empirical correlations of material and process factors with quality attributes of the final product. However, it seems also important to gain knowledge based on mechanistic considerations. Promising is here to study morphological and/or topological characteristics of particles and their aggregates. These geometric aspects must be taken into account to better understand how product attributes emerge from raw materials, which includes, for example, mechanical tablet properties, disintegration or dissolution behavior. Regulatory agencies worldwide are promoting the use of physical models in pharmaceutics to design quality into a final product. This review deals with pharmaceutical applications of theoretical models, focusing on percolation theory, fractal, and multifractal geometry. The use of these so-called fractal approaches improves the understanding of different aspects in the development of solid dosage forms, for example by identifying critical drug and excipient concentrations, as well as to study effects of heterogeneity on dosage form performance. The aim is to link micro- and macrostructure to the emerging quality attributes of the pharmaceutical solid dosage forms as a strategy to enhance mechanistic understanding and to advance pharmaceutical development and manufacturing processes.

Cubosomal based oral tablet for controlled drug delivery of telmisartan: formulation, in-vitro evaluation and in-vivo comparative pharmacokinetic study in rabbits

A nanoparticulate system; cubosomes has been suggested to support the controlled release of Telmisartan (TEL), a poorly water-soluble medication. Four distinctive formulae were selected according to the results of three estimated responses. The liquid cubosomes were successfully adsorbed onto Aerosil 380 to form granules. The formulae were evaluated for their flow properties. The best granules were compressed into tablets suitable for oral administration. The tablets were evaluated for its performance. The in vivo study of the best selected cubosomal tablets was checked after oral administration in the blood of albino rabbits utilizing an HPLC method. Results revealed that the highest EE was shown in formulae C5 (59.68 ± 1.3). All the prepared formulae had particle size less than 500 nm with PDI < 0.5 and the highest zeta potential results were observed in C5, C7, C9, C11 and C12 (>30 mv). A7 and A9 prepared using Aerosil 380 showed a perfect flowability. After 1 h of dissolution testing, the commercial product showed a 66% drug release while the release of all cubosomal formulae didn't exceed 35% during the first hour reaching a 85% of the drug released at the end of 24 h. A7 was selected for the in vivo study; T_max of TEL absorption is increased for cubosomal formula by three folds indicating sustained release pattern. The relative bioavailability is also increased by 2.6 fold. The investigation proposed the rationality of cubosome to figure an effective controlled release tablets to improve its bioavailability and expand its activity.

Quantitative surface topography assessment of directly compressed and roller compacted tablet cores using photometric stereo image analysis

Surface topography, in the context of surface smoothness/roughness, was investigated by the use of an image analysis technique, MultiRay™, related to photometric stereo, on different tablet batches manufactured either by direct compression or roller compaction. In the present study, oblique illumination of the tablet (darkfield) was considered and the area of cracks and pores in the surface was used as a measure of tablet surface topography; the higher a value, the rougher the surface. The investigations demonstrated a high precision of the proposed technique, which was able to rapidly (within milliseconds) and quantitatively measure the obtained surface topography of the produced tablets. Compaction history, in the form of applied roll force and tablet punch pressure, was also reflected in the measured smoothness of the tablet surfaces. Generally it was found that a higher degree of plastic deformation of the microcrystalline cellulose resulted in a smoother tablet surface. This altogether demonstrated that the technique provides the pharmaceutical developer with a reliable, quantitative response parameter for visual appearance of solid dosage forms, which may be used for process and ultimately product optimization.

Quantitative analysis of visible surface defect risk in tablets during film coating using terahertz pulsed imaging

Tablets are the most common form of solid oral dosage produced by pharmaceutical industries. There are several challenges to successful and consistent tablet manufacturing. One well-known quality issue is visible surface defects, which generally occur due to insufficient physical strength, causing breakage or abrasion during processing, packaging, or shipping. Techniques that allow quantitative evaluation of surface strength and the risk of surface defect would greatly aid in quality control. Here terahertz pulsed imaging (TPI) was employed to evaluate the surface properties of core tablets with visible surface defects of varying severity after film coating. Other analytical methods, such as tensile strength measurements, friability testing, and scanning electron microscopy (SEM), were used to validate TPI results. Tensile strength and friability provided no information on visible surface defect risk, whereas the TPI-derived unique parameter terahertz electric field peak strength (TEFPS) provided spatial distribution of surface density/roughness information on core tablets, which helped in estimating tablet abrasion risk prior to film coating and predicting the location of the defects. TPI also revealed the relationship between surface strength and blending condition and is a nondestructive, quantitative approach to aid formulation development and quality control that can reduce visible surface defect risk in tablets.

Investigation on Detergent Tablet Stability: from Raw Materials to Tablet Properties

The aim of this study is to investigate the functional characteristics (mechanical strength, disintegration and dissolution) of effervescent detergent tablets with chlorine provider under various storage conditions. The contribution of surfactant to the tablet stability was studied by comparing tablets without and with surfactant. After one year of storage in polypropylene tubes, the properties were modified for both formulas but the way to reach the end-point was different. In order to precise the influence of relative humidity, the tablets were exposed to controlled humidity levels, after a preliminary drying stage: with the surfactant, stability was better at lower humidity but for higher relative humidity, tablet properties were affected to a larger extent, compared to the formula without surfactant. Raman spectroscopy pointed out modifications of effervescent couple with humidity indicating i) a beginning of effervescence in the tablets and ii) the limiting effect of the surfactant on this phenomenon.

A systematic and mechanistic evaluation of aspartic acid as filler for directly compressed tablets containing trimethoprim and trimethoprim aspartate

The generally accepted paradigm of 'inert' and 'mono functional' excipient in dosage form has been recently challenged with the development of individual excipients capable of exhibiting multiple functions (e.g. binder-disintegrants, surfactant which affect P-gp function). The proposed study has been designed within the realm of multifunctionality and is the first and novel investigation towards evaluation of aspartic acid as a filler and disintegration enhancing agent for the delivery of biopharmaceutical class IV model drug trimethoprim. The study investigated powder characteristics using angle of repose, laser diffractometry and scanning electron microscopy (SEM). The prepared tablets were characterised using Heckel analysis, disintegration time and tensile strength measurements. Although Heckel analysis revealed that both TMP and TMP aspartate salt have high elasticity, the salt form produced a stronger compact which was attributed to the formation of agglomerates. Aspartic acid was found to have high plasticity, but its incorporation into the formulations was found to have a negative impact on the compaction properties of TMP and its salt. Surface morphology investigations showed that mechanical interlocking plays a vital role in binding TMP crystals together during compaction, while the small particle size of TMP aspartate agglomerates was found to have significant impact on the tensile strength of the tablets. The study concluded that aspartic acid can be employed as filler and disintegrant and that compactability within tablets was independent of the surface charge of the excipients.

Application and Characterization of Gum from Bombax buonopozense Calyxes as an Excipient in Tablet Formulation

This study was undertaken to explore gum from Bombax buonopozense calyxes as a binding agent in formulation of immediate release dosage forms using wet granulation method. The granules were characterized to assess the flow and compression properties and when compressed, non-compendial and compendial tests were undertaken to assess the tablet properties for tablets prepared with bombax gum in comparison with those prepared with tragacanth and acacia gums. Granules prepared with bombax exhibited good flow and compressible properties with angle of repose 28.60°, Carr's compressibility of 21.30% and Hausner's quotient of 1.27. The tablets were hard, but did not disintegrate after one hour. Furthermore, only 52.5% of paracetamol was released after one hour. The drug release profile followed zero order kinetics. Tablets prepared with bombax gum have the potential to deliver drugs in a controlled manner over a prolonged period at a constant rate.

Comparison between the effect of strongly and weakly cationic exchange resins on matrix physical properties and the controlled release of diphenhydramine hydrochloride from matrices

This study focused on investigating and comparing between the effect of the strongly cationic exchange resin, Dowex 88 (Dow88), and the weakly cationic exchange resin, Amberlite IRP64 (Am64), on the physical properties of matrices and their drug release profiles. The matrices were prepared by direct compression of Methocel K4M (HPMC) or Ethocel 7FP (EC) polymeric matrix formers and contained diphenhydramine hydrochloride as a model drug. The addition of Dow88 to the matrices decreased matrix hardness and increased thickness, diameter, and friability. In contrast, the addition of Am64 increased matrix hardness and maintained the original thickness, diameter, and friability. In deionized water, both resins lowered drug release from HPMC-based matrices by virtue of the gelation property of matrix former and the drug exchange property of embedded resin, in other words in situ resinate formation. Dow88 strongly dissociated and lowered the drug release to a greater extent than Am64, which was weakly dissociated. However, Am64 could retard drug release under simulated gastrointestinal conditions. EC-based matrices containing either resin displayed a propensity for disintegration caused by swelling and wicking (water adsorption) actions by the resin. The results of this study provided useful information on the utilization of ion exchange resins as release modifiers in matrix systems.

Pharmaceutical applications of AC biosusceptometry

AC Biosusceptometry offers an alternative to investigate noninvasively and without ionizing radiation the behavior of solid dosage forms in vitro and in the human gastrointestinal tract. This versatility allowed applying this technique in a wide field ranging from characterization of the disintegration process to elucidation of how the physiological parameters can interfere with pharmaceutical processes. It is increasingly important to understand how oral solid dosage forms behave in the human gastrointestinal tract. Once labelled, magnetic dosage forms provide an excellent opportunity to investigate complexes' interactions between dosage form and gastrointestinal physiology. In this paper, basic principles of this biomagnetic instrumentation and of the quantification based on magnetic images are reviewed. Also will be presented are some of the most recent applications of AC Biosusceptometry in the pharmaceutical research including oesophageal transit, gastric emptying and transit time of multiparticulate dosage forms, hydrophilic matrices and disintegration of tablets.

Evaluation of Tablet Formation of Different Lactoses by 3D Modeling and Fractal Analysis

The aim of this study was to use 3D modeling to differentiate not only among the four different types of lactose alpha-lactose monohydrate, spray-dried lactose, agglomerated lactose and lactose anhydrous but also between products from different manufacturers. Further "box-counting" fractal analysis of SEM images was done to gain additional information on tableting characteristics and tablet properties which can be found in the fractal structure. Twelve different materials from different manufacturers were analyzed for their powder-technological and physicochemical properties. They were tableted on an eccentric tableting machine at graded maximum relative densities and the recorded data, namely force, time, and displacement were analyzed by the 3D modeling technique. Tablet properties such as, elastic recovery, crushing force and morphology were analyzed. The results show that 3D modeling can precisely distinguish deformation behavior for different types of lactose and also for the same type of material produced with a slightly different technique. Furthermore, the results showed that the amorphous content of the lactose determined the compactibility of the material, which is due to a reversible exceeding of the glass transition temperature of the material. The three fractal dimensions DBW (box surface dimension), DWBW (pore/void box mass dimension), and DBBW (box solid mass dimension) are capable of describing morphological differences in lactose materials. Multivariate regression analysis showed that the fractal surface structure of the lactose-based materials is strongly correlated to tableting characteristics and tablet properties. Especially with regards to 3D modeling, it was found that the fractal indices can describe the parameters time plasticity d, pressure plasticity e, and fast elastic decompression, which is the inverse of omega. In addition, the 3D parameters are able to describe the powder and tablet fractal indices. In conclusion, the 3D modeling is not only able to characterize the compression process but it can also provide information on the final tablet morphology.

Effect of a pharmaceutical cationic exchange resin on the properties of controlled release diphenhydramine hydrochloride matrices using Methocel K4M or Ethocel 7cP as matrix formers

This work was aimed at evaluating the effect of a pharmaceutical cationic exchange resin (Amberlite IRP-69) on the properties of controlled release matrices using Methocel K4M (HPMC) or Ethocel 7cP (EC) as matrix formers. Diphenhydramine hydrochloride (DPH), which was cationic and water soluble, was chosen as a model drug. HPMC- and EC-based matrices with varying amounts (0-40%w/w) of resin incorporation were prepared by a direct compression. Matrix properties including diameter, thickness, hardness, friability, surface morphology and drug release were evaluated. The obtained matrices were comparable in diameter and thickness regardless of the amount of resin incorporation. Increasing the incorporated resin decreased the hardness of HPMC- and EC-based matrices, correlating with the degree of rupturing on the matrix surfaces. The friability of HPMC-based matrices increased with increasing the incorporated resin, corresponding to their decreased hardness. In contrast, the EC-based matrices showed no significant change in friability in spite of decreasing hardness. The incorporated resin differently influenced DPH release from HPMC- and EC-based matrices in deionized water. The resin further retarded DPH release from HPMC-based matrices due to the gelling property of HPMC and the ion exchange property of the resin. In contrast, the release from EC-based matrices initially increased because of the disintegrating property of the resin, but thereafter declined due to the complex formation between released drug and dispersed resin via the ion exchange process. The release in ionic solutions was also described. In conclusion, the incorporated resin could alter the release and physical properties of matrices.

Determination of the crushing strength of intact tablets using Raman spectroscopy

In the present study, the Raman spectroscopy technique was used as a non-invasive, rapid analytical method for measuring the crushing strength of tablets. The compressed tablets were individually detected, using Raman spectroscopy, and the respective crushing strength values were measured, using a tablet hardness tester as a reference method. The tablets were compressed from a granule mass containing theophylline anhydrate as an active substance. For measuring the crushing strength of the tablets, Raman spectra were recorded from the tablets. Partial least squares (PLS) regression models were constructed to obtain information from the spectra. The correlation between measured and predicted crushing strength values for the tablets was shown to be very favorable. With Raman spectroscopy, shifting of the baseline was observed as the crushing strengths of tablets (and the smoothness of the tablet surface) were increased. Consequently, correlation between the crushing strength data on the present tablets and Raman spectra was observed. Multiple scanning electron (SEM) and non-contact laser profilometry (LP) micrographs from the surfaces of the tablets were taken to describe the surfaces and applied as supportive information for the proposed spectroscopy approach. In conclusion, Raman spectroscopy is a promising alternative for established off-line/at-line tablet-testing methods for some tablet formulations.

Abrasion of tablets during scale-up: The influence of different crushing forces in laboratory and production perforated pan coaters

The purpose of this study was to investigate the influence of batch size during scale-up on the abrasion of biconvex tablets. Labelled tracer tablets of six different crushing forces (23-116 N) were mixed at different times and peripheral speeds in a laboratory (4 kg) and production (360 kg) perforated pan coater. The weight loss of these tracer tablets was determined. The main factor affecting the abrasion in both scales is the tablet crushing force as a nonlinear decrease in the abrasion was observed with increasing crushing force of the tablets. An increase in mixing time results in an increase in abrasion for the laboratory scale. In contrast to the production scale an influence of the peripheral speed on the abrasion could not be observed in laboratory scale. There is no difference in total abrasion for the laboratory scale and production scale for low peripheral speed. At higher peripheral speeds the abrasion in the production scale is slightly higher than in the laboratory scale.

Monitoring tablet surface roughness during the film coating process

The purpose of this study was to evaluate the change of surface roughness and the development of the film during the film coating process using laser profilometer roughness measurements, SEM imaging, and energy dispersive X-ray (EDX) analysis. Surface roughness and texture changes developing during the process of film coating tablets were studied by noncontact laser profilometry and scanning electron microscopy (SEM). An EDX analysis was used to monitor the magnesium stearate and titanium dioxide of the tablets. The tablet cores were film coated with aqueous hydroxypropyl methylcellulose, and the film coating was performed using an instrumented pilot-scale side-vented drum coater. The SEM images of the film-coated tablets showed that within the first 30 minutes, the surface of the tablet cores was completely covered with a thin film. The magnesium signal that was monitored by SEM-EDX disappeared after ~15 to 30 minutes, indicating that the tablet surface was homogeneously covered with film coating. The surface roughness started to increase from the beginning of the coating process, and the increase in the roughness broke off after 30 minutes of spraying. The results clearly showed that the surface roughness of the tablets increased until the film coating covered the whole surface area of the tablets, corresponding to a coating time period of 15 to 30 minutes (from the beginning of the spraying phase). Thereafter, the film only became thicker. The methods used in this study were applicable in the visualization of the changes caused by the film coating on the tablet surfaces.

The application of non-contact laser profilometry to the determination of permanent structural change induced by compaction of pellets

Microcrystalline (MCC) pellets of different structural and mechanical properties were produced by the process of extrusion and spheronization from the formula MCC:water:ethanol (5:3:2) using four different drying techniques, namely: freeze-drying, fluid-bed drying, hot air oven drying and desiccation with silica-gel. Six hundred milligrams of these pellets were compacted by 130 MPa to flat-faced tablets and stored for 48 h in ambient temperature and humidity after which their permanent structural change (plastic deformation) was investigated in terms of surface roughness parameters using a non-contact laser profilometer. The results were compared with the deformability values measured as a reciprocal of the slope of the force/displacement curve obtained during diametral compression test of the individual pellets. Based on the different rate of moisture removal, means of heat and mass transfer, and static and dynamic nature of the bed the different drying techniques produced pellets of different porosity, strength and deformability. The increase in deformability of the pellets with the increase of porosity was illustrated by the reduction of the surface roughness parameters. Analysis of variance identified the significant difference in the mean rugosity values of the tablets from the pellets produced by the various drying techniques. The deformability values obtained were reasonably comparable to those plasticity values explained in terms of the inverse of the slope of the force/displacement curves. The laser profilometry technique was able to quantify the permanent structural change of the pellets after compaction in terms of mean rugosity values. The methodology was able to incorporate a wide variety of deformable pellets of the same formulations but produced by different drying techniques. The porous freeze-dried pellets produced the smoothest tablet surface profile, while the other techniques increased the rugosity values in ascending order from fluid-bed drying, desiccation with silica-gel to hot air oven drying technique.

The application of non-contact laser profilometry to the determination of permanent structural changes induced by compaction of pellets

Pellets of different mechanical properties were produced by extrusion and spheronisation process based on various composition (microcrystalline cellulose (MCC), lactose, glyceryl monostearate (GMS), water, ethanol and glycerol). Six hundred milligrams of these pellets were compacted at two different pressures (86.7 and 130MPa) to form flat-faced tablets and stored for 48h in ambient temperature and humidity after which their permanent structural change (plastic deformation) was investigated in terms of surface roughness parameters of both faces of the tablets, using a non-contact laser profilometer. The results were compared with the deformability values obtained from the force/displacement curve as well as the phase angle values obtained from the dynamic scan of a dynamic mechanical analyser. The increase in deformability of the pellets with the increase in porosity, increase in the contents of GMS, lactose or ethanol in the formulations and increase in compaction pressure was illustrated by the reduction of the surface roughness parameters. Analysis of variance identified the significant difference in the mean rugosity values of the tablets from the various formulations, tablet faces and compaction pressures. The deformability values obtained were reasonably comparable to those plasticity values obtained in terms of phase angle from the dynamic scan of the DMA and the force/displacement curves. The laser profilometry technique in conjunction with scanning electro-microscopy (SEM) demonstrated the low and broad based wavelike structure of the pellets after compaction rather than spiky sharp protrusions. This confirms the capability of determining the plastic deformability of the pellets from the surface roughness parameters obtained from non-contact laser profilometry.

A novel technique for imaging film coating defects in the film-core interface and surface of coated tablets

Confocal laser scanning microscopy (CLSM) was introduced and examined as a novel technique for imaging film-core interface and surface defects of film-coated tablets. Tablets of acetylsalicylic acid, microcrystalline cellulose (MCC) and lactose monohydrate were film-coated with aqueous hydroxypropyl methylcellulose using an instrumented side-vented pan coater. The film coatings were applied using 100- and 500-kPa spraying air pressures. The CLSM images of the coating surface were compared with surface roughness measurements using a laser profilometer and an optical roughness analyzer. The spraying air pressure affected the film-core interface and the occurrence of coating defects. With the lower spraying pressure the aqueous coating solution penetrated into the tablet core, the core components migrated to the coating layer, and the film coating surface was clearly rougher compared to the higher spraying pressure. Storage at 25 degrees C/60% RH or 40 degrees C/75% RH for 3 months expanded the MCC-containing tablet core impaired the film structure and increased the film roughness. Based on the present results, CLSM is an effective tool for imaging film-core interface and surface defects of film-coated tablets. The CLSM images are supported by the results obtained with the other surface roughness measuring techniques.

Influence of the Aqueous Film Coating Process on the Properties and Stability of Tablets Containing a Moisture‐Labile Drug

The effects of an aqueous film coating process on the morphology and storage stability of hydroxypropyl methylcellulose-coated tablets containing a moisture-labile model drug (acetylsalicylic acid, ASA) were evaluated using an instrumented side-vented tablet pan coater. Coating parameters studied were inlet air absolute humidity 5 g/m3 and 12 g/m3, spraying air pressure 100 kPa and 500 kPa, pan air temperature 35 degrees C and 55 degrees C, and coating solution flow rate 2.2 g/min and 7.8 g/min. The surface roughness of the coatings was measured with a laser profilometer and the chemical hydrolysis of the model drug ASA with an UV-spectrophotometer. The film-coated tablets were stored at 25 degrees C/60% RH and 40 degrees C/75% RH for three months. The high absolute humidity of the inlet air increased the residual water content and surface roughness of the coated tablets. Using a lower coating solution flow rate, higher spraying air pressure and pan temperature the coatings were smooth and homogeneous. In both ambient and accelerated storage conditions, the roughness of the coatings and the hydrolysis of ASA increased, but this was independent of the film coating process. Uniform and smooth hydroxypropyl methylcellulose coatings can be achieved by improved control of process parameters related to the application of the coating solution and water evaporation of the tablet surface.

Tablet surface characterisation by various imaging techniques

The aim of this study was to characterise tablet surfaces using different imaging and roughness analytical techniques including optical microscopy, scanning electron microscopy (SEM), laser profilometry and atomic force microscopy (AFM). The test materials compressed were potassium chloride (KCl) and sodium chloride (NaCl). It was found that all methods used suggested that the KCl tablets were smoother than the NaCl tablets and higher compression pressure made the tablets smoother. Imaging methods like optical microscopy and SEM can give useful information about the roughness of the sample surface, but they do not provide quantitative information about surface roughness. Laser profilometry and AFM on the other hand provide quantitative roughness data from two different scales, laser profilometer from 1 mm and atomic force microscope from 90 microm scale. AFM is a powerful technique but other imaging and roughness measuring methods like SEM, optical microscopy and laser profilometry give valuable additional information.

Development of an automation system for a tablet coater

An instrumentation and automation system for a side-vented pan coater with a novel air-flow rate measurement system for monitoring the film-coating process of tablets was designed and tested. The instrumented coating system was tested and validated by film-coating over 20 pilot-scale batches of tablets with aqueous-based hydroxypropyl methylcellulose (HPMC). Thirteen different process parameters were continuously measured and monitored, and the most significant ones were logged for analysis. Laser profilometry was used to measure the surface roughness of the coated tablets. The instrumentation system provided comprehensive and quantitative information on the process parameters monitored. The measured process parameters and the responses of the film-coated tablet batches showed that the coating process is reproducible. The inlet air-flow rate influenced the coating process and the subsequent quality of the coated tablets. Increasing the inlet flow rate accelerated the drying of the tablet surface. At high inlet flow rate, obvious film-coating defects (ie, unacceptable surface roughness of the coated tablets) were observed and the loss of coating material increased. The instrumented and automated pan-coating system described, including historical data storage capability and a novel air-flow measurement system, is a useful tool for controlling and characterizing the tablet film-coating process. Monitoring of critical process parameters increases the overall coating process efficiency and predictability.

Effect of compression force on the crystal properties of erythromycin acistrate tablets

The crystal properties of compressed and powdered erythromycin acistrate tablets were studied by the X-ray powder diffraction (XRPD) method. Detailed analysis of X-ray powder diffraction line profiles was performed. Diffraction peak intensities and full width at half maximum (FWHM) values of the peaks corresponding to three different crystal lattice directions were determined. Crystallite size was calculated by Scherrer's equation using the data of integral breadth of the peaks. The preferred orientation of the crystallites is also discussed. According to the results, the crystallite size increased on the tablet surface after a small compression force (4 kN) in all crystal lattice directions studied. Even small compression forces caused recrystallization. With higher compression forces (8-18 kN) the crystallite size and the FWHM values remained rather constant. After the compression force of 18 kN the peaks in different crystal lattice directions behaved differently. In the lattice directions of diffraction maxima 2 and 3, the effect was the same with the small (4 kN) and the high compression force (22 kN). Further recrystallization occurred with 22 kN. However, in the crystal lattice direction of diffraction maximum 1 at the compression force of 8 kN the crystallite broke and crystallinity decreased. These were not seen in the powdered tablet samples. It could be concluded that the effect of compression force on the crystal properties of erythromycin acistrate tablets was seen on the tablet surface but not in the powdered tablets. Compression force also affected the preferred orientation of crystallites on the tablet surface and especially in the lattice direction of diffraction maximum 3. This was not seen in the powdered tablets.