Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Tablets – lozenges – or pills
Reexamination Certificate
2000-11-02
2002-12-24
Robinson, Allen J. (Department: 1616)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Tablets, lozenges, or pills
C424S423000, C606S077000, C514S025000
Reexamination Certificate
active
06497901
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the general area of drug-delivery systems that are based on resorbable matrices. Sustained and/or controlled release of medicinal agents and other bioactive substances are the primary uses of these systems.
BACKGROUND OF THE INVENTION
Polymer matrices designed for controlled release of bioactive compounds can be non-resorbable or resorbable. In general, resorbable means degradable in the body by erosion from the surface or breakdown from within. The mechanism can involve either a chemical reaction, such as hydrolysis, or dissolution.
Non-resorbable polymers, such as polymethylmethacrylate, have been used for antibiotic delivery. These materials suffer from the disadvantage that they must be retrieved, which involves a second intervention and entails the risk of infection (HW Bucholz, et al., (1970)
Chiburg,
43, 446).
Resorbable polymer matrices for controlled release are usually based on an oxygenated monomer, which is condensed in organic solvent to yield the polymeric product. The bioactive agent and the polymer are then combined in such a way as to give a timed-release formulation. The combination of active ingredient and polymer often involves organic solvents as well. The use of organic solvents is a decided disadvantage, especially when large-scale production is required. Toxic residues of organic solvents are a concern. Proteins and many polypeptides are incompatible with organic solvents.
The types of polymers in this category include:
polyesters
polyanhydrides
polyketals
poly(orthoesters)
polyurethanes
(Burkersroda, F V and Goepferich, A M in
Biomedical Materials,
T Neenan, M Marcolongo and R F Valentini, eds. (1999), page 23, Materials Research Society, Warrendale Pa.).
Naturally occurring proteins may be used as structural components in drug-delivery matrices (Royer, U.S. Pat. No. 4,349,530; Royer, U.S. Pat. No. 5,783,214; Lee,
Science
(1981) 233-235). One deficiency of proteinaceous delivery matrices is that they can exhibit instability especially in environments where an inflammatory reaction is present such as a site of localized sepsis.
WO 99/15150 discloses a stable, yet practical composition for use in inflamed sites comprising an inorganic compound, a matrix polymer and/or a complexing agent. This composition has the advantage of being biocompatible but, unlike synthetic organic polymers, no non-aqueous solvents are required in the preparation. The drug is incorporated as a solid or as part of the matrix polymer solution. The material can also be used as a cement, that is, it can be injected directly into a lesion and allowed to solidify in situ.
OBJECTS OF THE INVENTION
It is an object of this invention to provide a safe resorbable delivery system that can be designed and fashioned to provide controlled release of bioactive substances over a pre-determined time-course.
It is an object of this invention to provide a delivery matrix which when installed as an injectable liquid can solidify in the presence of moisture.
It is an object of this invention to provide a delivery matrix with enhanced stability in acidic and neutral media.
It is an object of the present invention to provide a delivery matrix with improved molecular complexing agents.
SUMMARY OF THE INVENTION
The subject invention relates to a delivery matrix formed by mixing:
a. an inorganic compound capable of undergoing hydration and/or crystallization, plus,
b. a conditioning agent which improves stability, extends the residence time, and provides for control of the release profile, and optionally,
c. a matrix polymer, and/or
d. a complexing agent.
Mixing a bioactive agent with the above components results in a solid composition that is capable of providing sustained release of said agent over a predetermined time period.
DETAILED DESCRIPTION OF THE INVENTION
A. Introduction
The inorganic compound-conditioning agent composites described herein are resorbable by dissolution. No acid is produced as opposed to hydrolytic erosion of polymer matrices such as polyesters.
The inorganic-conditioning agent composite described herein requires no organic solvent in matrix preparation or drug loading. No acid is produced on erosion so it is useful for orthopedic applications. The inclusion of the conditioning agent and advantageously the matrix polymer imparts control over the release profile of the active ingredient and distinguishes this material from unadulterated plaster of Paris which is rigid and safe but is otherwise lacking in performance (D Mackey, et al. (1982)
Clin. Orthop.
167, 263; G W Bowler, et. al. (1994) J. Trauma, 36, 331). The matrix described in commonly-owned WO 99/15150 may also contain a complexing agent to retard the release of the active ingredient.
The matrix formulation of this invention contains improved hydrophobic complexing agents, e.g., pamoates, and conditioning agents which can serve as water repellants. Water repulsion of these matrices allows for set-up in an aqueous environment. In fact, when a conditioning agent is present, the matrix will solidify when totally submerged. This trait is important when the material is used in orthopedic or dental applications. Examples include filling of periodontal defects or treating an osteomyelitic lesion. Also, the lifetime in the environment, or the body, is extended. This extended residence time is important in the delivery profile. Multiple formulations with different residence times can be combined. The resultant release profile has a desirable form and resembles zero-order. When hydrophobic complexing agents and conditioning agents are used with hydrophobic medicinal agents, the release profiles can be controlled.
Entrapment of bioactive substances within the resorbable biocompatible matrix described herein yields a delivery system, which permits controlled and localized release of a bioactive agent. Inorganic compounds such as CaSO
4
—1/2 H
2
O (calcium sulfate hemihydrate) can be combined with a polymer in the presence of a bioactive agent to produce a solid which constitutes a biocompatible and resorbable delivery matrix (See WO 99/15150—the entire contents of which is incorporated by reference herein). The matrix polymer increases the internal viscosity of the device, which slows the efflux of the bioactive agent.
The production of and advantageous embodiment of the delivery system can be illustrated as follows:
When contacted with water, calcium sulfate hemihydrate is converted to the dihydrate, CaSO
4
—2 H
2
O, which crystallizes. The mass of needle-like crystals produces a porous matrix with high compressive strength, as much as 2000 psi or more. A conditioning agent such as calcium stearate is pre-mixed with the calcium sulfate hemihydrate. The slurry can be injected into the desired location with solidification in situ. This composition is ideal for dental and orthopedic applications. The fact that the slurry can set-up in the presence of moisture is very advantageous.
The delivery matrix is formed by mixing:
a. an inorganic compound capable of undergoing hydration and/or crystallization, plus
b. a conditioning agent, and optionally
c. a matrix polymer, and/or
d. a complexing agent.
The nature and amount of matrix polymer, the relative proportions of calcium sulfate hemihydrate and liquid, the complexing agent, and the nature and amount of the conditioning agent permit the adjustment of the release profile and residence time of the matrix.
The use of a conditioning agent such as calcium stearate provides improved stability and added control of the release profile and residence time. In addition, it imparts the desirable feature of moisture resistance, which preserves the shape of the mass while setting. When the composition containing calcium stearate is fully submerged after thorough blending, the mass remains intact and setting occurs. This attribute is very important as it allows the installation of the composition into moist areas such as a tooth socket or bone lesion. Water repulsion can also stabilize the solid dosage form with extension of residence time. Ca
Dewitty Robert M.
Nixon & Vanderhye P.C.
Robinson Allen J.
Royer Biomedical, Inc.
LandOfFree
Resorbable matrices for delivery of bioactive compounds does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Resorbable matrices for delivery of bioactive compounds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Resorbable matrices for delivery of bioactive compounds will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2994074