Amiodarone-related cyclic thyroid dysfunction.
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Adolescent↗
Biomedical subjects
R C Rowe
Publications and source records attributed to R C Rowe.
The effect of lactose particle size on the extrusion properties of microcrystalline cellulose-lactose mixtures.
Ram extrusion has been used to assess and compare the flow characteristics and quality of wet powder masses formed from mixtures of water with microcrystalline cellulose and two different particle size samples of lactose. The force-displacement profiles can reveal poor flow properties. Steady state flow was achieved for the mixture containing fine lactose which produced an extrudate of uniform moisture content at all extrusion rates except the lowest (5 cm min-1). Increasing the lactose particle size significantly altered the extrusion properties of the formulation with forced flow predominating and high extrusion pressures observed. Formulations showing that type of extrusion are to be avoided as they produce poor quality extrudate which may be unsuitable for spheronization. Flow visualization studies showed that problems associated with such mixtures are caused by failure to maintain a constant angle of convergence during extrusion, which is essential for maintenance of steady state flow. With the mixture made with coarse lactose, the extrudate quality could be improved by extruding at high velocities, information that may be of significance in the development of formulations for large-scale production. Differences between formulations may be expressed quantitatively by plotting the apparent shear stress-shear rate relationship. The curves are modified by the particle size of lactose included in the mixtures. Such curves have implications in predicting the suitability of an extrudate, produced under particular experimental conditions, for spheronization.
Cellulose↗
Characterization of the sphericity of particles by the one plane critical stability.
A method has been developed to characterize the roundness of particles in terms of the angle necessary to tilt a plane such that the particles would roll, the 'one plane critical stability'. The method is based on determination of the centre of gravity of the particle from a digitized image of the coordinates of its outline and computing the angle necessary to incline a plane such that the centre of gravity moves outside the boundary of the particle. The method is particularly applicable to differentiate between the various shapes formed during the production of spherical granules by extrusion/spheronization.
Microscopy↗
Thermal studies on the interaction of water and microcrystalline cellulose.
The interaction between water and microcrystalline cellulose in the absence and presence of lactose has been studied by thermogravimetric analysis, differential thermal analysis and immersional calorimetry. The results indicate that most of the water held within a system used for the preparation of spherical granules by extrusion/spheronization is present as free water which may be readily lost by evaporation. There is approximately 0.856 mol of water per 100 g of microcrystalline cellulose which appears to be absorbed as structured water. Microcrystalline cellulose may therefore be described as a 'molecular sponge'. The enthalpy of fusion of the 'free' water offers a simple method of estimating the effective surface area of the microcrystalline cellulose.
Calorimetry↗
Water distribution in creams prepared using cetostearyl alcohol and cetrimide.
The water distribution in an antiseptic cream formulation prepared using cetostearyl alcohol and cetrimide has been studied using thermogravimetric analysis, differential scanning calorimetry, ultracentrifugation and scanning electron microscopy. In addition to a free water phase two types of interlamellarly fixed water were found, one associated with the liquid crystalline network around the oil droplets and one associated with the liquid crystalline network of the bulk. The latter was in equilibrium with the free water and can be classed as freely drainable.
Cetrimonium↗
A quantitative assessment of the reactivity of the fatty alcohols with cetrimide using immersion calorimetry.
The reactivity of the fatty alcohols with cetrimide has been quantitatively assessed using immersion calorimetry. In all cases the reaction was endothermic i.e. it had a positive enthalpy. For the n-alcohols the reactivity, as evaluated by the rate of enthalpy change, decreased with increasing chain length although branching on the tetradecanol and hexadecanol resulted in a higher reactivity. Adding 1-octadecanol to 1-hexadecanol resulted in an increased reactivity rising to a maximum for mixtures containing 20-40% w/w 1-octadecanol. The results have been interpreted in terms of the polymorphic form of the alcohol.
Calorimetry↗
The effect of the relationship between punch velocity and particle size on the compaction behaviour of materials with varying deformation mechanisms.
The effect of punch velocity over the range 0.033-300 mm s-1 on the compaction properties of lactose, microcrystalline cellulose and a drug substance (a phthalazine derivative) for a range of particle sizes has been studied using the yield pressure derived from the Heckel relationship and a strain rate sensitivity index (SRS index), as the criteria to describe their behaviour. For lactose, a material which deforms by a mixed mechanism of particle fracture and plastic deformation at the contact points, the yield pressure increased and the SRS index decreased as particle size decreased, due to a reduction in the amount of fragmentation of the particles. For microcrystalline cellulose, a material which is known to deform plastically, the yield pressure and the SRS index were independent of particle size. For the phthalazine derivative the yield pressure increased as particle size decreased; however the SRS index reduced from 41% to zero, indicating that the deformation mechanism was changing from plastic flow to brittle behaviour. This decrease in the SRS index has been explained in terms of the relative amounts of strain-hardened material produced as milling severity increased, resulting in an increasing resistance to deformation and thus an apparent increase in brittle behaviour as particle size decreased.
Cellulose↗
The prediction of compatibility/incompatibility in blends of ethyl cellulose with hydroxypropyl methylcellulose or hydroxypropyl cellulose using 2-dimensional solubility parameter maps.
Typical two dimensional solubility parameter maps for ethyl cellulose, hydroxypropyl methylcellulose and hydroxypropyl cellulose have been constructed using literature data. The maps of the polymers showed some degree of overlap indicating some mutual compatibility. Compatibility between ethyl cellulose and hydroxypropyl cellulose was greater than between ethyl cellulose and hydroxypropyl methylcellulose. The maps may also be used to predict the effect of added plasticizers.
Cellulose↗
Brittle fracture propensity measurements on 'tablet-sized' cylindrical compacts.
The brittle fracture propensity test which was originally designed for large, square compacts with a central hole has been modified and extended to compacts of 'tablet-sized' dimensions. This allows a brittle fracture propensity (BFP) index to be measured at strain rates and conditions approaching those normally used in tableting. The BFP indices for microcrystalline cellulose, Tablettose and heavy magnesium carbonate were evaluated at punch velocities of 3.33 and 200 mm s-1 and found to be in good agreement with the results of previous workers.
Hardness↗
Localized cracking around pigment particles in tablet film coatings: a theoretical approach.
The problem of localized cracking around pigment particles in tablet film coatings has been treated as being analogous to stress cracking in two phase ceramics. For this purpose a simple model of a spherical cavity in an infinite isotropic medium has been used. As well as allowing the estimation of the stresses generated by the differences in thermal expansion of the dispersed pigment and the polymer matrix, the model predicts the effect of some formulation variables. The predictions are in agreement with the observed cracking on film-coated tablets.
Chemistry, Pharmaceutical↗
The effect of punch velocity on the compaction of a variety of materials.
The effect of punch velocity over the range 0.033-400 mms-1 on the compaction of a variety of materials has been studied using constants derived from the Heckel equation as criteria to describe their behaviour. For materials known to deform plastically, e.g. maize starch and polymeric materials, there was an increase in the yield pressure with punch velocity attributable to a change either from ductile to brittle behaviour or a reduction in the amount of plastic deformation due to the time dependent nature of plastic flow. For materials known to consolidate by fragmentation, e.g. magnesium and calcium carbonates, there was no change in yield pressure with increasing punch velocity. The data has been analysed in terms of the strain rate sensitivity of the materials calculated from their yield pressure at low and high punch velocities.
Acetaminophen↗
The effect of temperature on the conductivity of gels and emulsions prepared from cetrimide and cetostearyl alcohol.
The conductivity of gels and emulsions containing cetrimide, cetostearyl alcohol, liquid paraffin and water has been studied over the temperature range +35 to -10 degrees C. All samples froze at temperatures below -5 degrees C and exhibited hysteresis on rewarming to room temperature with an initial increase in conductivity up to 15 degrees C followed by a decrease to 25 degrees C. The amount of hysteresis was dependent on the cetostearyl alcohol content and appeared to be related to changes in the microstructure of the liquid crystalline network.
Cetrimonium↗
A photometric analysis of tablet movement in a side-vented perforated drum (Accela-Cota).
A novel particle tracing technique has been used to study the effect of the normal process variables i.e. drum speed, drum loading and the presence/absence of mixing elements (baffles) on the movement of tablets in a side-vented perforated drum (24 in diameter Accela-Cota). The technique involves measuring the duration of light emission from a single luminous tablet using a photomultiplier mounted to scan the same area as a spray gun, and has enabled the quantification of both the time that the tablet spends on the surface per pass (surface time) and the time that the tablet spends within the bulk of the tablet bed (circulation time) over run lengths equating to the normal tablet coating cycle. The technique also allows the study of the uniformity of tablet appearances by means of circulation profiles. It was found that, while both the surface and circulation times decreased with increasing drum speed and loading, there was irregularity of tablet appearance especially at low drum speeds and in the absence of baffles.
Photometry↗
The characterization of wet powder masses suitable for extrusion/spheronization.
The characterization of the flow of wet powder masses has been achieved using a ram extruder. Force/displacement curves obtained when material is forced through dies of varying length were found to exhibit three stages: (1) compression (2) steady state flow and (3) forced flow. To provide high quality extrudate it was found preferable to ensure that the compression stage was as short as possible and that steady state flow predominated. To produce these conditions, an optimum composition, die length and ram speed were required. The implications of these findings in relation to the provision of suitable formulations and production conditions for the preparation of spherical granules are discussed.
Cellulose↗
Gloss measurement on film coated tablets.
The gloss of film coated tablets has been assessed using a commercially available specular glossmeter modified to measure the specular reflectance of individual flat-faced, film-coated tablets. For all the pigmented film formulations studied, there was a decrease in gloss with increasing pigment concentration, the magnitude of the decrease being dependent on the pigment used. Film coatings prepared using an aqueous coating system had a much lower gloss reading than those prepared using an organic solvent coating system. Increasing the mean particle size of an inert filler particle resulted in a minimum gloss reading at intermediate particle sizes, while increasing the polymer concentration resulted in a significant decrease in gloss. In the latter case a power law equation was found to fit the data relating the percentage decrease in gloss with the percentage increase in roughness. The results are consistent with the known theories of specular reflectance and illustrate the potential of this rapid and simple technique in the optimization of film formulation and process variables during product development.
Particle Size↗
An investigation of the structural changes occurring in a cetostearyl alcohol/cetrimide/water gel after prolonged low temperature (4 degrees C) storage.
Structural changes in a ternary gel prepared using the mixed emulsifier system of cetrimide and cetostearyl alcohol after prolonged low temperature (4 degrees C) storage have been studied using freeze-etch transmission electron microscopy and other techniques. The system changed from an opaque smooth gel of high viscosity, low conductivity and low free water, to a pearlescent milky lotion of low viscosity, high conductivity and high free water. Subsequent equilibration of the thinned system to room temperature (25 degrees C) over 48 h produced an opaque granular gel of similar consistency, but slightly higher conductivity and higher free water than the initial sample. Microscopical examination by both differential interference contrast and freeze-etch electron microscopy showed the system changed from one consisting of a liquid crystalline network localized around cetostearyl alcohol particles, to a system consisting of large waxy plates coexisting with some residual liquid crystalline network. A supportive mechanism for the thinning of the ternary gel at prolonged low temperature storage has been inferred by comparing data with that produced by other workers studying the fusion of phospholipid membranes considered to be morphologically similar to the liquid crystalline network observed in this ternary gel.
Cetrimonium↗
Flow defects in wet powder mass extrusion.
Surface impairment, in the form of the flow defects roughness and sharkskinning, has been shown to occur with microcrystalline cellulose/lactose/water mixes on extrusion under varying process conditions. These defects result from the imbalance of stresses at the outer wall of the extrudate on leaving the die and can be avoided by changing the process conditions that are known to affect these stresses, e.g. the length of the die, the velocity of throughput and the moisture content of the formulation.
Humidity↗
Reflectance measurements on gels and emulsions containing cetrimide and cetostearyl alcohol--a preliminary investigation.
Various light scattering properties-the reflectivity, contrast ratio and scattering index of a series of gels and emulsions containing cetrimide, cetostearyl alcohol, water and liquid paraffin have been examined using reflectance measurements made at 560 nm using a four-filter, tristimulus colorimeter. The scattering properties of both systems were dependent on the total interfacial surface area of either the dispersed unreacted cetostearyl alcohol and/or the dispersed droplets of liquid paraffin, and hence increased with increasing concentration of both ingredients. For the emulsion containing liquid paraffin, the scattering properties increased linearly with the concentration of liquid paraffin but with the ternary gel system the scattering properties were not directly related to cetostearyl alcohol concentration. This was confirmed by microscopy as due to the changes in the size of the dispersed unreacted cetostearyl alcohol. The results illustrate the potential of this simple, reproducible non-destructive technique in the study of the structure of such systems.
Cetrimonium↗