Multiply-coated particles

Details Multiply-coated particles Multiply-coated particles

1995-09-29

1998-06-30

Page, Thurman K.

Drug, bio-affecting and body treating compositions

Preparations characterized by special physical form

Particulate form

424489, 424405, 424486, 47 576, A61K 916, A61K 950

Patent

active

057730300

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/EP94/00880 filed Mar. 21, 1994.
The present invention relates to multiply-coated biologically active particles, a process for preparing such coated particles and a method of using these particles in sustained-release formulations.
Encapsulation techniques are known and described, for example, in U.S. Pat. No. 4,938,797. The processes known to coat solid particulate active substances suffer from a number of disadvantages: due to the irregular geometry of particulate matter, coating is usually incomplete and the user risks skin-contact with the active substance. Furthermore, the problems of non-linear and/or incomplete release include environmental damage due to residual active substance, and unpredictable efficacy rates.
A process for the preparation of controlled release agrochemical granules is described in Indian patent specification 167769. In this process the active substance, embedded in a polyhydric polymer, represents only 3 to 31% by weight of the encapsulated granule. The release characteristics are shown by example to be non-linear.
P. G. Shukla et al. describe in J. Controlled Release, 15, p. 153 to 166 (1991) crosslinked starch-urea formaldehyde as a matrix for encapsulation of carbofuran. Release profiles of carbofuran are illustrated, however the amount of active substance is small, namely 3 to 20% by weight of the encapsulated particle, and the particle size is relatively large, ranging from 700 to 2000 .mu.m. The rate of release of active substance is not constant, but follows an asymptotic course.
In U.S. Pat. 4,696,822 there are described compositions of mono-walled microencapsulated insecticides but the rate of release is not constant, falling after an initial burst.
In EP patent application 0 079668 A1 granules are described comprising the pesticide in a solid core, such core then being coated with at least one layer of a particular membrane selected from the group of dienes and an unsatturated fatty acid radical. The application of plural layers is also described each layer increasing the thickness of the coating, but no discrete phase boundary being formed between each layer.
Microencapsulated agricultural chemicals are described in published PCT application WO 91/04661. Microencapsulation by curing of a prepolymer may be accomplished in a single stage or in repeated stages. The polymer layers form a homogeneous coating which is a mono-coating since the repeated stages are carried out in the same reaction mixture by adding fresh hardener and/or prepolymer. The rate of release of active ingredient is rapid to begin with, but falls after an initial burst.
There is a need for a more efficient and predictable sustained-release delivery system for biologically active substances. A particular need is found in agriculture where the release characteristics of granular pesticide delivery systems tend to comprise a strong initial burst, followed by an ever-diminishing rate of release of the active substance. A constant rate of release can be illustrated graphically by a linear relationship between time and the amount of active substance released.
Coated granules are not sprayable. Microparticles, on the other hand, can be dispersed easily in water and are therefore sprayable, e.g. by the farmer or horticulturalist.
Surprisingly it has now been found that much-improved sustained release rates of active substance can be achieved with particulate, particularly microparticulate, biologically active substances coated by at least two layers of polymeric material in which there is a discrete phase-boundary formed between each coating layer and between the active substance and the first coating layer. The coating thus formed is heterogeneous since each successive layer is applied to a sub-layer around which a boundary surface has already formed. It has been found that in this way, high initial release rates of the prior art can be suppressed. This is especially useful when the active substance is a pesticide. Moreover handling safety is improved, and a reduced amount of

REFERENCES:
patent: 4696822 (1987-09-01), Matsumura et al.
patent: 4938797 (1990-07-01), Hasslin et al.
patent: 5129180 (1992-07-01), Stewart
Journal of Controlled Release, 15 (1991), pp. 153-166.

Affiliated with

Also associated with

Rating

Multiply-coated particles does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Multiply-coated particles, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multiply-coated particles will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1856283