Title:  Drug delivery via conformal film

United States Patent:  6,309,380

Appl. No.:  238946

A drug delivery conformal film system according to the present invention is adapted to be compounded and applied, by medical personnel at the point of use, to a medical device such as a cardiovascular and urology stent, pacemaker, vascular graft, suture ring of mechanical heart valve, implantable infusion port, implantable drug delivery pump, orthopedic hardware and appliance, and, neurological stimulating device. The drug delivery conformal film consists of one of three in vivo biocompatible; biodegradable, bio-erodable or bioabsorbable embodiments: (1) cross-linked sodium alginate, (2) UV photo-active polymer, or, (3) hydrogels. An implantable medical device such as the stent or suture ring of a mechanical artificial heart valve is coated with an in vivo biocompatible; biodegradable or bioerodable or bioabsorbable solution comprising a polymer and containing a drug, the solution is cross-linked or cured to form a film on the device immediately prior to placement in the body. When the coated device is introduced into the body, the drug contained in the coating is released in a local region. The invention provides a point of use in vivo drug delivery system whereby the drug and its concentration can be selected by medical personnel immediately prior to implantation of the medical device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be discussed in detail with reference to the preferred embodiments. Unless otherwise stated, all percentages represent weight percent.

Drugs or other biologically active materials incorporated into the drug delivery conformal film system of the present invention are intended to perform a variety of functions, including, but not limited to: anti-clotting or anti-platelet formation, and the prevention of smooth muscle cell growth on the vessel wall. Drugs anticipated for delivery include antibiotics, anticoagulants, tissue generation factor, and angiogenesis drugs. Drugs also include, but are not limited to, anti-thrombogenic drugs (heparin, PPACK, enoxaprin, aspirin, coumadin, hirudin, TPA, urokinase, and streptokinase), anti-proliferative drugs (monoclonal antibodies, heparin, angiopeptin, enxoaprin, methotrexate, cisplatin, flourouracil, Adriamycin), antimetabolites, thromboxane inhibitors, non- steroidal and steroidal anti-inflammatory drugs, Beta and Calcium channel blockers, genetic materials (including DNA and RNA fragments), and bioactive materials (such as fibronectin, laminin, elastin, collagen, and intergrins).

As stated previously, the drug delivery conformal film of the present invention comprises one of three in vivo biocompatible; biodegradable, bio-erodable or bio-inert embodiments: (1) cross-linked sodium alginate, (2) UV photo-active polymer, or, (3) hydrogels, for example, thermal irreversible hydrogels. Of these embodiments, cross-linked sodium alginate is preferred.

Sodium alginate is preferred because of its biocompatibility and in vivo biodegradability, and cross-linking film forming properties. A sterile and low endotoxin form of sodium alginate has recently become available under product number K8P569 from Monsanto, 800 N. Lindbargh Blvd. St. Louis, Mo., or under product number UP MVG from Pro Nova, Strandveien 18, N-1324 Lysaker, Norway. Very low endotoxin levels can be obtained in alginates by use of a highly specialized purification process. Alginates in a water gel form have the unique ability to form elastic films by reaction with calcium salts and/or magnesium salts. Once cross-linked, these films retain their shape and resist stress.

The preferred embodiment of the present invention is a medical release drug delivery conformal film system comprised of sterile, low endotoxin sodium alginate and sterile low-pyrogen water which uses a solution of calcium chloride to achieve gelation through cross-linking. The sodium alginates selected for this invention have a Mannuronic acid content of approximately 58 to 62% and a Guluronic acid content of approximately 42 to 38%. The alginate films thus produced have known and acceptable long-term biocompatibility and biodegradability in vivo and are manufactured in such a manner and form that renders the film sterile and biocompatible with human tissue, organs and body fluids. Sodium alginate in purified form, such as Monsanto part number K8P569 and ProNova part number UP MVG as a solution in water containing acceptably low levels of pyrogens is the preferred composition that demonstrates the desired in vivo biocompatibility and known in vivo biodegradability.

Alginates, such as sodium alginate, form aqueous solutions in either liquid or gel form. The addition of increasing amounts of non-aqueous water-miscible solvents (i.e., glycols) to an alginate solution increases the solubility of non-water-soluble compounds. As the alginate solution in this invention is intended to serve as a drug delivery film, non-water soluble drugs can be added to an alginate solution prepared with up to 10% propylene glycol, or other biocompatible solvents, substituted for water. Alternatively, water and the particular glycol may be mixed prior to the addition of the alginate. Furthermore, the drug may be added to the water/glycol mixture prior to the addition of the alginate.

Sodium alginates gel by cross-linking between a pH range of 3 to 5. Calcium chloride has been selected for its low pH and in vivo biocompatible characteristics to cross-link the algin gel creating a strong film. Alginates, when cross-linked with calcium chloride form a biodegradable/bioabsorbable film that is lubricious and thus provides a lubricating coating. This lubricious coating can assist in the insertion of the medical device into the human body.

Sodium alginate used in the embodiments of this invention may also include Monsanto Keltone HVCR. A formulation was prepared from the HVCR grade that represents the mannuronic acid and guluronic acid content that will produce suitable solutions of algin and is similar in characterizations to Monsanto part number K8P569 and ProNova part number UP MVG which is the most preferred alginate polymer of the invention. This solution has an acceptable viscosity, film forming rheology and film mechanical properties, and produces an in vivo biocompatible solution and film.

The alginate solution can be used to coat an implantable medical device, at its point of use, whereby the high viscosity alginate solution, to which a drug has been added, is rendered into a film by dipping the coated device into calcium chloride. To restrict the film to the exterior and perforations of a device, the internal diameter of the device can be blocked off, for example with a balloon, during the coating process. Over an extended period of time, through its biodegradable characteristics, the film can deliver a controlled amount of a drug that was added to the alginate solution at the point of use, in known concentration over such extended period of time. The drug may be delivered either uniformly or nonuniformly depending on the uniformity of the coating thickness.

For the following examples, non-sterile Monsanto alginate part number HVCR was used whose properties are comparable to the purified form Monsanto part number K8P569 alginate and ProNova part number UP MVG.

In order to produce a biocompatible conformal film solution, application of Good Manufacturing Procedures (GMP) and use of sterile, low endotoxin sodium alginate and sterile, low endotoxin 10% calcium chloride solutions, are recommended to ensure raw material and finished product quality.

In the preferred embodiment of this invention, sodium alginate is mixed with sterile, low-pyrogen water, which is also known as "water for injection," to form a solution. Sodium alginate concentration amounts of about 1% to about 8% by weight and of various molecular weights, in the range of 12,000 to 190,000 with a preferred molecular weight of 120,000 to 190,000 can be used to form a pourable solution tailored to rheological properties desired for the application.

Proper blending techniques are necessary to dissolve the lyophilized sodium alginate in water. A high-shear mixer, which creates vortex, is recommended. The mixing blade is placed off center in the mixing container. The mixing blade is positioned near the bottom of the solution to avoid introducing excessive air. The lyophilized alginate is slowly sifted into the vortex. The application of heat aids in dissolving the alginate powder. While blending, slowly elevate the heat to 135 degrees Fahrenheit and mix for approximately 30 minutes.

Claim 1 of 17 Claims

What is claimed is:

1. A method of producing an implantable drug-deliverable medical device at a point of use, said method comprising:

providing an implantable medical device,

coating said device with an in vivo biocompatible and biodegradable or bioabsorbable or bioerodable liquid or gel solution containing a polymer, said solution comprising a desired dosage amount of one or more predetermined drugs,

converting said liquid or gel solution to a film adhering to said medical device thereby forming said implantable drug-deliverable medical device,

wherein the steps of coating and converting are carried out at said point of use of said implantable medical device.

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