Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Web – sheet or filament bases; compositions of bandages; or...
Reexamination Certificate
2000-05-08
2003-12-30
Page, Thurman K. (Department: 1615)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Web, sheet or filament bases; compositions of bandages; or...
C424S443000, C525S218000, C525S221000, C525S222000, C525S223000, C525S224000, C525S225000, C525S226000, C525S227000, C525S228000, C525S229000, C525S230000, C525S301000, C525S302000, C156S326000, C156S327000
Reexamination Certificate
active
06669953
ABSTRACT:
RELATED APPLICATIONS
This application claims priority from application 9714650.0 which was filed in the United Kingdom on Jul. 11, 1997.
The present invention relates to block copolymers useful in transdermal patches as adhesives and/or drug retention means, as well as to transdermal patches comprising such block copolymers.
Transdermal patches are well known in the pharmaceutical industry and are used to deliver drugs into the skin of a patient. Drug delivery by use of a transdermal patch has a number of advantages over oral delivery methods. For example, the drug may be provided continuously over a long period, rather than in spaced apart, higher doses, and the patches are easy to apply and use.
The patch must have an adhesive portion, to allow the patch to adhere to the skin. An adhesive suitable for use in a transdermal patch should possess certain properties, including adhesion, tack and cohesion. Adhesion refers to the force with which the adhesive sticks to a surface. Tack refers to the speed at which the adhesive can form a bond with the surface, while cohesion refers to the internal strength of an adhesive and its ability to resist splitting when placed under external stress. Good cohesion, in particular, is necessary for clean removal of the transdermal patch.
A primary use of the adhesive may be to affix a patch to the skin. However, it is preferable for the drug to be delivered to be incorporated into the adhesive, where possible, in order to reduce the amount of components and, therefore, expense necessary to make the patch.
A number of adhesives are already available for se in transdermal patches. Acrylic polymers are commonly used, as these possess adhesive properties which may easily be modulated by changing the composition of the polymer.
In connection with transdermal patches, U.S. Pat. No. 5,413,776 discloses the use of a copolymer adhesive consisting of an acrylic acid ester polymer portion in combination with an N-vinyl-2 pyrrolidone polymeric portion. EP-A-450986 discloses the use of an alkyl methacrylate (co)polymer in combination with silicic acid anhydride, specifically for the delivery of nicotine. Both adhesives are acrylic copolymers.
EP-A-0450986 further discloses that a multi-functional monomer may be included as a copolymer, to provide chemical cross-links between the copolymer strands. Chemical cross-linking is thought to increase the degree of polymerisation and, thus, cohesion of the adhesive.
Block copolymers have also been used as adhesives for transdermal patches. A block copolymer consists of a mixture of ‘hard’ (A) and ‘soft’ (B) segments, which may be combined in an A-B-A or (A-B)
n
type structure (c.f. Block Copolymers: Overview and Critical Survey, Noshay and McGrath, 1977). Association of the hard segments is thought to provide a degree of physical cross-linking, which improves the cohesive properties of the adhesive. One such example of a block copolymer adhesive is a polystyrene-polyisoprene-polystyrene (SIS) which is an A-B-A type block copolymer adhesive made by Shell, for example. This adhesive requires the use of an additional tackifier to provide suitable tack to the adhesive.
U.S. Pat. No. 5,066,728 discloses a multiblock copolymer comprising endblocks of phenylbutadiene and an elastomeric midblock of a conjugated diene such as isoprene or butadiene. The copolymer is cross-linkable by electron beam radiation, such that the crosslinks are confined primarily to the end-block domains in the polymer, with minimal crosslinking occurring in the rubbery matrix. Blends of the copolymer with tackifier resins provide curable pressure sensitive adhesives.
JP-62036412A discloses vinyl chloride resins, produced by a graft copolymerisation of vinyl chloride and a block copolymer, wherein the copolymer contains a soft segment that is crosslinked. The resins reportedly have a excellent impact resistance, weather-proofing properties and bending elasticity.
WO-97/01589 also discloses graft copolymers, suitable for use in influencing optical quality, dyeabilty, stability to weather or impact cracking and stress cracking in moulding compositions. The graft copolymers comprise a soft segment with at least one acrylate monomer, and a hard segment comprising at least one vinyl aromatic monomer. The soft segment is cross-linked, and the hard and soft segments are overlaid.
While a number of adhesives are available for use in transdermal patches, there is still a need for transdermal patch adhesives which possess excellent tack, cohesion and improved drug storage capacity.
It has now, surprisingly, been found that a degree of chemical cross-linking between the soft segments of a block copolymer can cause the copolymer to have enhanced properties, particularly with regard to cohesion and drug storage properties.
Thus, in a first aspect, the present invention provides a cross-linked block copolymer having drug retention properties, the block copolymer having hard and soft segments, characterised in that there is cross-linking between the soft segments.
Preferably, the block copolymer is an acrylic block copolymer. It is also preferred that the block copolymer is capable of acting as an adhesive, preferably on its own, but also in conjunction with one or more substances, such as those typically used in the manufacture of transdermal patches.
Thus, in a preferred aspect, there is provided a block copolymer, preferably an acrylic block copolymer, comprising soft and hard segments, that is suitable for use as an adhesive, characterised in that there is a degree of chemical cross-linking between the soft segments.
It will be appreciated that the term ‘drug’, as used herein, refers to any substance or compound suitable for administration via a transdermal patch. A substance having drug retention properties is taken herein as being a substance capable of absorbing or adsorbing a drug. In the instance where the substance is loaded with drug for dispensing via a transdermal patch, then it will be appreciated that such absorbance and/or adsorbance should be at least partially reversible.
The block copolymers of the present invention are simple to manufacture in an economic fashion, and may be selected for their drug retention and/or adhesive/cohesive properties. Accordingly, it is possible to provide an adhesive for use with a transdermal patch which allows the delivery of a greater amount of drug than is currently possible using known adhesives, as well as providing cleaner removal of used patches.
The term ‘block copolymer’, as used herein, refers to a macromolecule comprised of two, or more, chemically dissimilar polymer structures, terminally connected together (Block Copolymers: Overview and Critical Survey, Noshay and McGrath, 1977). These dissimilar polymer structures, sections or segments, represent the ‘blocks’ of the block copolymer. The blocks may generally be arranged in an A-B structure, an A-B-A structure, or a multiblock-(A-B)
n
-system, wherein A and B are the chemically distinct polymer segments of the block copolymer.
It is generally preferred that the block copolymer of the present invention is of an A-B-A structure, especially wherein one of A and B is an acrylic type polymeric unit. It will be appreciated that the present invention is also applicable to block copolymers which possess three, or more different ‘blocks’, such as an A-B-C block copolymer. However, for convenience, reference hereinafter to block copolymers will assume that there are only A and B sub-units, but it will be appreciated that such reference also encompasses block copolymers having more than two different sub-units, unless otherwise specified.
It will be appreciated that the properties of block copolymers are very largely determined by the nature of the A and B blocks. Block copolymers commonly possess both ‘hard’ and ‘soft’ segments. A ‘hard’ segment is a polymer that has a glass transition temperature (T
g
) and/or a melting temperature (T
M
) that is above room temperature, while a soft segment is a polymer that has a T
g
(and possibly a T
M
) below room temperatu
Fish & Richardson P.C.
Ghali Isis
Page Thurman K.
Strakan Limited
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