Effervescent systems using reaction doping agents

Details Effervescent systems using reaction doping agents Effervescent systems using reaction doping agents

1993-12-29

1995-05-16

Page, Thurman K.

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Tablets, lozenges, or pills

424464, A61K 946

Patent

active

054158702

DESCRIPTION:

BRIEF SUMMARY
The invention relates to an effervescent tablet as can be prepared, for example, by the process according to WO 88/00009. The composition and preparation of effervescent systems known to date are based on a mixture of organic, edible acids with carbon dioxide-forming alkalis and/or alkaline earths which are granulated together or reacted together, dried and compressed with active substances. In this process, all substances are present in more or less powdered or finely crystalline form, and the properties of the resulting product corresponding to the statistical cross-section of the components of the mixture.
In the known effervescent system stated at the outset, the carrier crystal has a reactive core of, for example, citric acid on the inside but monosodium citrate on the outside, as formed ad hoc by individual reaction. The particle thus has the chemical properties of monosodium citrate on the outside; on the inside, however, it still consists of citric acid. Thus, when the first layer of monosodium citrate is dissolved away on contact with water, there is a vigorous reaction with the natural citric acid present within the core.
For various reasons, it is desirable to put pharmaceutical formulations on the market in the form of effervescent tablets: on the one hand, many patients have difficulties in swallowing, particularly in the case of large tablets; on the other hand, many active substances should be taken with at least some water, even if only a modest amount, so that they do not come into contact in concentrated form with the gastric mucus membrane. There have been two problems with effervescent tablets to date: On the one hand, there are many active substances which are themselves moisture-sensitive or react with one of the components of the effervescent system when moisture is present and thus cannot be readily stored, particularly because the citric acid generally used virtually always has a small residual moisture content of 0.2-0.4%. It has therefore been necessary to date to rely in general on very expensive, moisture-resistant packagings.
Even very readily soluble active substances present problems because they rapidly form concentrated solutions when they begin to dissolve in water and thus hinder or slow down the reaction of the effervescent components with one another.
On the other hand, very large effervescent tablets having a total weight of in general 3-4 g have been required to date, particularly for large active substance doses of, for example, 1 g per dose, for achieving acceptable dissolution times, which tablets in turn require large amounts of liquid for dissolution; however, many patients do not readily consume such large amounts of liquid. Moreover, they are expensive with regard to both material required and packaging and may introduce large amounts of undesirable sodium ions into the patient's body. Finally, large effervescent tablets often have a buffer capacity or acid-consuming capacity which is undesirably high for certain applications.
A further difficulty arises from the necessity of using binders in order in the first place to be able to compress the effervescent mixtures to give stable, sufficiently hard tablets. Such binders, such as, for example, sorbitol, polyvinylpyrrolidone, etc., increase the hardness of effervescent tablets but considerably slow down the disintegration and make the tablets additionally moisture-sensitive.
Attempts have already been made to increase the shelf life of sensitive active substances in effervescent tablets by using, for example, anhydrous potassium carbonate (U.S. Pat. No. 3,136,692) as the gas-forming component or monosodium citrate (DE-A1 3920626 or U.S. Pat. No. 4,689,218) as the acidic component; however, such tablets then require a very long time for dissolution because potassium carbonate itself reacts with citric acid much more slowly than, for example, sodium bicarbonate, or the latter reacts much more slowly with monosodium citrate than with citric acid.
For freely soluble active substances, a combination of disintegration

REFERENCES:
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patent: 4127645 (1978-11-01), Witzel et al.
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Database WPIL, Section Ch, Week 8219 Derwent Publications Ltd., London, GB; AN 82-38452E & JP,A,57 056 434 (Kao Soap KK) 5 Apr. 1982.

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