Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Particulate form
Patent
1995-01-19
1997-09-02
Webman, Edward J.
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Particulate form
424426, 514772, 428402, 264 46, A61K 916
Patent
active
056629389
DESCRIPTION:
BRIEF SUMMARY
The invention relates to novel bioresorbable-polymer microspheres free from surface-active agent, their preparation and their application.
The encapsulation of active substances in polymer matrices, in order to protect these active substances or to release them gradually, is well known.
Various systems are known in particular, these also being known as delayed effect systems, which gradually release pharmacologically active principles of therapeutic value, which are dispersed in a polymer matrix, into the body in which they are implanted. The polymers used may be derived from natural polymers (cellulose or proteins) or may be synthetic polymers.
Among the materials which may be implanted into the body, bioresorbable polymers, that is to say polymers which degrade gradually in the body and the degradation products of which polymers are removed by metabolism or by excretion, are particularly advantageous, especially since they circumvent the need for surgical intervention which is intended to remove the implant after its period of operation. This is the case for polyesters derived from hydroxy acids. These polyesters are also known by abbreviation as poly(hydroxy acid)s.
The bioresorbable sustained-release systems may also be in the form of microspheres which may be administered orally, intramuscularly or intravenously.
The term microsphere is understood here to refer to a solid spherical system the average diameter of which does not exceed a few hundred micrometers (in particular 500 .mu.m), this concept encompassing spheres (sometimes referred to as nanospheres) with an average diameter of less than a micrometer.
The main advantage of the microspheres is that they enable active principles, having a prolonged period of action by virtue of their gradual release, to be administered readily by injection, thereby enhancing the therapeutic action of these active principles and reducing the possible toxicity thereof. This method avoids the installation of implants which may be the source of inflammations or of infections. It also avoids repeated administrations since the active principle exerts its action over a longer period.
Microspheres containing no active principle are also therapeutically useful: they may serve especially to bring about the embolization of angiomas.
Microspheres may be obtained by various techniques, especially according to the so-called solvent evaporation method. This method may be described as follows: the active principle to be encapsulated and the polymer which constitutes the microspheres are dissolved in a water-immiscible volatile organic solvent. The resulting solution is emulsified using a surface-active agent. Gradual evaporation of the organic solvent leads to the conversion of the droplets of the emulsion into solid microspheres in which the active principle is trapped.
This technique thus involves a surface-active agent whose function is to promote the stability of the emulsion and thus to guarantee the correct formation of the microspheres and the stability of the suspensions of the latter in liquid injection media.
However, the presence of a surfactant at the surface of the microspheres, in a body, is liable to modify the characteristics and the performance of the delayed effect system and even to make it unusable if the surfactant is toxic, or if it is strongly bound to the surface, since it modifies the body/synthetic polymer material interface. Indeed, it is this interface Which controls the release of the active principle and the response of the implantation medium.
One of the surfactants best adapted to the production of polymer-based microparticles is polyvinyl alcohol (PVA), which gives rise to very little formation of particle agglomerates and which enables microspheres with a size of less than 150 .mu.m to be obtained readily. However, the use of PVA raises potential toxicity problems. The reason for this is that this compound is considered to be potentially carcinogenic, particularly when it is administered parenterally.
Thus, the use of a surfactant of any nature,
REFERENCES:
patent: 4818542 (1989-04-01), DeLuca et al.
patent: 5180765 (1993-01-01), Sinclair
R. Bodmeier et al., International Journal of Pharmaceutics, 51 (1989) 1-8.
Coudane Jean
Schwach Gregoire
Ustariz Christine
Vert Michel
Centre National de la Recherche Scientifique "CNRS"
Webman Edward J.
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