Tablet drug release

This equipment has one calibrator tablet a single tablet product, chlorpheniramine extended-release tablets (drug-release calibrator, single unit). It has been found that this equipment is not particularly sensitive to vibration and has reliable and consistent operation (17). 

In the case of non-swelling tablets, drug release is generally expressed by Fickian diffusion, for which n = 0.5. For most erodible matrices, the drug release follows zero order kinetics, for which n = 1. In the case of swelling tablets, the drug release is due to a combination of swelling and erosion. They follow non-Fickian release behavior. For them, the value of n lies between 0.5 and 1.0 [78]. The value of n was calculated from the slopes of the log(M/M ) vs log t plot in acidic and neutral pH. 

One of the most commonly used methods of modulating tablet drug release is to include it in a matrix system. In addition, the drug release is a function of many factors, including the chemical nature of the membrane, geometry and its thickness, and the particle surface of the drug device, the physico chemical nature of the active substance and the interaction between the membrane and the permeating fluids are also important [116]. 

Implants are small, sterile cylinders of dmg, inserted beneath the skin or into muscle hssue to provide slow absorption and prolonged achon therapy. This is principally based on the fact that such dmgs, invariably hormones, are almost insoluble in water and yet the implant provides a rate of dissoluhon sufficient for a therapeuhc effect. The British Pharmacopoeia (1993) describes one implant, testosterone. The United States National Formulary (1990) also ineludes oestradiol. Implants are made fiom the pure drug into tablet form by compression or fusion. No other ingredient can be included sinee this may be insoluble or toxie or, most importantly, may influence the rate of drug release. 

In order to produce an adequate tablet formulation, certain requirements, such as sufficient mechanical strength and desired drug release profile, must be met. At times this may be a difficult task for the formulator to achieve, due to poor flow and compactibility characteristics of the powdered drug. This is of particular importance when one only has a small amount of active material to work with and cannot afford to make use of trial-and-error methods. The study of the physics of tablet compaction through the use of instrumented tableting machines (ITMs) enables the formulator to systematically evaluate his formula and make any necessary changes. 

Wu et al. [46] used the approach of an artificial neural network and applied it to drug release from osmotic pump tablets based on several coating parameters. Gabrielsson et al. [47] applied several different multivariate methods for both screening and optimization applied to the general topic of tablet formulation they included principal component analysis and... 

Extensions of BCS beyond the oral IR area has also been suggested, for example to apply BCS in the extended-release area. However, this will provide a major challenge since the release from different formulations will interact in different ways with in vitro test conditions and the physiological milieu in the gastrointestinal tract. For example, the plasma concentration-time profile differed for two felodipine ER tablets for which very similar in vitro profiles had been obtained, despite the fact that both tablets were of the hydrophilic matrix type based on cellulose derivates [70], This misleading result in vitro was due to interactions between the gel strength of the matrix and components in the dissolution test medium of no in vivo relevance. The situation for ER formulations would be further complicated by the need to predict potential food effects on the drug release in vivo. 

Abrahamsson, B., Johansson, D., Torstensson, A., Wingstrand, K., Evaluation of solubilizers in the drug release testing of hydrophilic matrix extended-release tablets of felodipine, Pharm. Res. 1994, 2 2, 1093-1097. 

Marvola, M., Aito, H., Pohto, P., Kannikoski, A., Nykanen, S., Kokkonen, P., Gastrointestinal transit and concomitant absorption of verapamil from a single-unit sustained-release tablet, Drug Dev. Ind. Pharm. 1987, 13, 1593-1609. 

It should be remembered that in 1970, when drug-release/dissolution tests first became official through the leadership of USP and NF, marketed tablets or capsules in general simply did not have a defined dissolution character. They were not formulated to achieve a particular dissolution performance, nor were they subjected to quality control by means of dissolution testing. Moreover, the U.S. Food and Drug Administration (FDA) was not prepared to enforce dissolution requirements or to even to judge their value. 

USP 27 (2004) contains 185 capsule monographs representing 121 monographs with dissolution test and 15 other monographs with a drug-release test. Out of 527 tablet monographs, 346 contain a dissolution test while 21 cited a drug-release test (14). 

Costa P, Sousa Lobo JM. Influence of dissolution medium agitation on release profiles of sustained-release tablets. Drug Dev Ind Pharm 2001 27 811-817. 

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