Tablet structure

One should note that BC represents a highly elastic material as little plastic deformation or brittle fracture has occurred. Also, sharp differences between the slope CD and DE are indicative of weak, or failed, tablet structures. The RDWF estimated from these plots can provide a good indication of the ejection force. More detailed treatments of such studies are now in the open literature, to which the interested reader is referred [118-120],... 

Furthermore, the concentration point at which a component is starting to percolate the system is usually related to a change in the properties of the system, which will now be more affected by this component. This is known as a critical point. Close to the critical point important changes can take place, for example, changes in the release mechanism of the active agent and modification of the tablet structure (e.g., monolith versus a desegregating device). 

The mechanism of action of disintegrating agents has been the subject of some debate. Some substances such as starch swell when they come into contact with water, and disruption of the tablet structure has been attributed to this. However, other effective disintegrants do not swell in this way, and are believed to act by providing a network of hydrophilic pathways inside the tablet through which water can diffuse. Irrespective of the precise mechanism of disintegration, it is clear that water uptake into the tablet must be the first step in the disintegration process. ... 

The consequences of such a force distribution on tablet strength can be profound. Particle deformation, whether elastic or plastic, will be proportional to the force applied, and as has been discussed, this deformation is an essential preliminary to the formation of the interparticulate bonds on which tablet integrity depends. Thus, the porosity of the tablet, and hence its strength, will vary within the tablet. The weakest points in the tablet structure will be those that receive the lowest force i.e., on the face of the tablet adjacent to the stationary punch and on the central axis near to the moving punch. Thus, because of its non-uniform density, some parts of a tablet are stronger than others. 

Mechanochemical co-crystallisation has also been exploited in the synthesis of readily compressible and thermodynamically stable forms of the API paracetamol (Figure 8.8(b)). While tablet formation using the thermodynamically stable polymorph of paracetamol is difficult, the metastable orthorhombic polymorph yields tablets much more readily due to its layered crystal structure. Consequently, it was expected that co-crystals of paracetamol with a similar layered structure would also be readily compressible. Screening by LAG revealed four co-crystals of paracetamol with improved ability to compress into tablets. Structural characterisation and Density Functional Theory (DFT) calculations revealed that enhanced compressibility was related to the formation of a sheet-like structure reminiscent of the second polymorph of paracetamol (Figure 8.8(c)-(e)). ... 

You will see, by examining this structure, that aspirin is an ester of acetic acid. Aspirin is mankind s most widely used drug. Somewhat over 20 million pounds of aspirin are manufactured each year in the United States alone This amounts to something like ISO five-grain tablets for every person in the country ... 

Tablets Biological, physicochemical, and structural parameters used to derive QSAR Eq. 19 ...

Water Uptake. There is evidence to suggest that water uptake caused by capillary forces is the crucial factor in the disintegration process of many formulations. In such systems the pore structure of the tablet is of prime importance and any inherent hydrophobicity of the tablet mass will adversely affect it. Therefore, disintegrants in this group must be able to maintain a porous structure in the compressed tablet and show a low interfacial tension towards aqueous fluids. Rapid penetration by water throughout the entire tablet matrix to facilitate its breakup is thus achieved. Concentrations of disintegrant that ensure a continuous matrix of disintegrant are desirable and levels of between 5 and 20% are common. 

MOLECULAR STRUCTURE. In their attempts to identify the mechanism(s) of action of tablet disintegrants, researchers recently have turned their... 

It is also important to appreciate that the behavior on decompression can markedly affect the characteristics of the finished tablets, because the structure must be strong enough to accommodate the recovery- and ejection-induced stresses. Indeed, tablet strength is a direct function of the number of surviving bonds in the finished tablet. In addition, ability to monitor... 

The bioavailability of drugs from tablets can be markedly influenced by the rate and efficiency of the initial disintegration and dissolution process. Unfortunately, one is faced with a compromise situation — a structure that has both a durable structure prior to administration and the ability to readily break down when placed in the in vivo environment. One of the major factors affecting both these properties is the structure of the tablet, in particular its density (or porosity) and the pore structure. Study of the significance of such measurements and interpretation of the results is a relatively recent field of interest. 

This technique has also been used in combination with nitrogen absorption to study the pore structure of some excipients, particularly MCC in both the powdered and compacted state. The intraparticulate porosity of MCC has been shown to be unaffected by tableting the interparticular pores, however, are gradually reduced in size [38]. Recently this method has been used to evaluate the internal structure of tablets prepared from microcapsules [150]. 

The rate at which selected liquids penetrate into tablets can be used to study their pore structure. A knowledge of the rate of liquid penetration should also provide information on the disintegration/dissolution behavior of a tablet on administration. Such investigations are capable of forming a valuable link between physico-mechanical characteristics and in vivo performance. 

Fig. 40a, b. NSE spectra of a dilute solution under 0-conditions (PDMS/ d-bromobenzene, T = = 357 K). a S(Q,t)/S(Q,0) vs time t b S(Q,t)/S(Q,0) as a function of the Zimm scaling variable ( t(Q)t)2/3. The solid lines result from fitting the dynamic structure factor of the Zimm model (s. Tablet) simultaneously to all experimental data using T/r s as adjustable parameter. 

Hardness data for only two amino acids were found in the literature. They are glycine and alanine. They are the smallest of the amino acids. Both consist of rather flat tablet-like collections of atoms that form layered crystal structures in which the molecular sub-groups within the layers are held together by hydrogen bonds (Albrecht and Corey, 1939), and the molecules by London forces. Their hardnesses are ... 

The pore structure of a solid can contribute to the disintegration, dissolution, adsorption, and diffusion of a drug material [26,27]. Because of this, porosity and pore size distribution measurements have been used extensively to study tablets [28-30], granules [31,32], and excipients [33]. The following classification system of pore sizes has been developed based on the average pore radii [6] ... 

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