the invention is directed to a medical device in the form of an implantable structure , which is coated with a homogenous matrix comprising a pharmaceutical substance and a biodegradable , biocompatible , non - toxic , bioerodible , bioabsorbable polymer matrix . the structure of the device has at least one surface and comprises at least one or more based materials . the based materials can be selected from stainless steel , nitinol , mp35n , gold , tantalum , platinum or platinum irdium , or other biocompatible metals and / or alloys such as carbon or carbon fiber , cellulose acetate , cellulose nitrate , silicone , cross - linked polyvinyl alcohol ( pva ) hydrogel , cross - linked pva hydrogel foam , polyurethane , polyamide , styrene isobutylene - styrene block copolymer ( kraton ), polyethylene teraphthalate , polyurethane , polyamide , polyester , polyorthoester , polyanhidride , polyether sulfone , polycarbonate , polypropylene , high molecular weight polyethylene , polytetrafluoroethylene , or other biocompatible polymeric material , or mixture of copolymers thereof ; polyesters such as , polylactic acid , polyglycolic acid or copolymers thereof , a polyanhydride , polycaprolactone , polyhydroxybutyrate valerate or other biodegradable polymer , or mixtures or copolymers , extracellular matrix components , proteins , collagen , fibrin or other bioactive agent , or mixtures thereof . the medical device of the invention can be any device that is introduced temporarily or permanently into a mammal for the prophylaxis or therapy of a medical condition . these devices include any that are introduced subcutaneously , percutaneously or surgically to rest within an organ , tissue or lumen of an organ , such as arteries , veins , ventricles or atrium of the heart . medical devices may include stents , stent grafts , covered stents such as those covered with polytetrafluoroethylene ( ptfe ), expanded polytetrafluoroethylene ( eptfe ), or synthetic vascular grafts , artificial heart valves , artificial hearts and fixtures to connect the prosthetic organ to the vascular circulation , venous valves , abdominal aortic aneurysm ( aaa ) grafts , inferior venal caval filters , permanent drug infusion catheters , embolic coils , embolic materials used in vascular embolization ( e . g ., cross - linked pva hydrogel ), vascular sutures , vascular anastomosis fixtures , transmyocardial revascularization stents and / or other conduits . the coating composition on the medical device comprises one or more pharmaceutical substances incorporated into a polymer matrix so that the pharmaceutical substance ( s ) is released locally into the adjacent or surrounding tissue in a slow or controlled - release manner . the release of the pharmaceutical substance in a controlled manner allows for smaller amounts of drug or active agent to be released for a long period of time in a zero order elution profile manner . the release kinetics of a drug further depends on the hydrophobicity of the drug , i . e ., the more hydrophobic the drug is , the slower the rate of release of the drug from the matrix . alternative , hydrophilic drugs are released from the matrix at a faster rate . therefore , the matrix composition can be altered according to the drug to be delivered in order to maintain the concentration of drug required at the site for a longer period of time . the invention , therefore , provides a long term effect of the drugs at the required site which is more efficient in preventing restenosis and minimizes the side effects of the released pharmaceutical substances used . the matrix can be selected from a variety of polymer matrices . however , the matrix should be biocompatible , biodegradable , bioerodible , non - toxic , bioabsorbable , and with a slow rate of degradation . biocompatible matrices that can be used in the invention include , but are not limited to , poly ( lactide - co - glycolide ), polyesters such as polylactic acid , polyglycolic acid or copolymers thereof , polyanhydride , polycaprolactone , polyhydroxybutyrate valerate , and other biodegradable polymer , or mixtures or copolymers , and the like . in another embodiment , the naturally occurring polymeric materials can be selected from proteins such as collagen , fibrin , elastin , and extracellular matrix components , or other biologic agents or mixtures thereof . polymer matrices used with the coating of the invention such as poly ( lactide - co - glycolide ); poly - dl - lactide , poly - l - lactide , and / or mixtures thereof are of various inherent viscosities and molecular weights . for example , in one embodiment of the invention , poly ( dl lactide - co - glycolide ) ( dlplg , birmingham polymers inc .) is used . poly ( dl - lactide - co - glycolide ) is a bioabsorbable , biocompatible , biodegradable , non - toxic , bioerodible material , which is a vinylic monomer and serves as a polymeric colloidal drug carrier . the poly - dl - lactide material is in the form of homogeneous composition and when solubilized and dried , it forms a lattice of channels in which pharmaceutical substances can be trapped for delivery to the tissues . the drug release kinetics of the coating on the device of the invention can be controlled depending on the inherent viscosity of the polymer or copolymer used as the matrix and the amount of drug in the composition . the polymer or copolymer characteristics can vary depending on the inherent viscosity of the polymer or copolymer . for example , in one embodiment of the invention using poly ( dl - lactide - co - glycolide ), the inherent viscosity can range from about 0 . 55 to 0 . 75 ( dl / g ). poly ( dl - lactide - co - glycolide ) can be added to the coating composition from about 50 to about 99 % ( w / w ) of the polymeric composition . fig1 shows a stent partially coated with the coating comprising poly ( dl - lactide - co - glycolide ) polymer matrix . the poly ( dl - lactide - co - glycolide ) polymer coating deforms without cracking , for example , when the coated medical device is subjected to stretch and / or elongation and undergoes plastic and / or elastic deformation . therefore , polymers which can withstand plastic and elastic deformation such as poly ( dl - lactide - co - glycolide ) acid - based coats , have advantageous characteristics over prior art polymers . the rate of dissolution of the matrix can also be controlled by using polymers of various molecular weight . for example , for slower rate of release of the pharmaceutical substances , the polymer should be of higher molecular weight . by varying the molecular weight of the polymer or combinations thereof , a preferred rate of dissolution can be achieved for a specific drug . alternatively , the rate of release of pharmaceutical substances can be controlled by applying a polymer layer to the medical device , followed by one or more than one layer of drugs , followed by one or more layers of the polymer . additionally , polymer layers can be applied between drug layers to decrease the rate of release of the pharmaceutical substance from the coating . the malleability of the coating composition of the invention can be further improved by varying the ratio of lactide to glycolide in the copolymer . that is , the ratio of components of the polymer can be adjusted to make the coating more malleable and to enhance the mechanical adherence of the coating to the surface of the medical device and aid in the release kinetics of the coating composition . in this embodiment of the invention , the polymer can vary in molecular weight depending on the rate of drug release desired . the ratio of lactide to glycolide can range , respectively , from about 50 - 85 % to 50 - 15 % in the composition . by adjusting the amount of lactide in the polymer , the rate of release of the drugs from the coating can also be controlled . the characteristic biodegradation of the polymer , therefore , to some degree determines the rate of drug release from the coating . information on the biodegradation of polymers can be obtained from the manufacturer information , for example , from birmingham polymers . the principle mode of degradation for the lactide and glycolide polymers and copolymers is hydrolysis . degradation proceeds first by diffusion of water into the material followed by random hydrolysis , fragmentation of the material and finally a more extensive hydrolysis accompanied by phagocytosis , diffusion and metabolism . the hydrolysis is affected by the size and hydrophillicity of the particular polymer , the crystallinity of the polymer and the ph and temperature of the environment . in general , the degradation time will be shorter for low molecular weight polymers , more hydrophillic polymers , more amorphous polymers and copolymers higher in glycolide . therefore at identical conditions , low molecular weight copolymers of dl lactide and glycolide , such as 50 / 50 dl - plg will degrade relatively rapidly whereas the higher molecular weight homopolymers such as l - pla will degrade much more slowly . once the polymer is hydrolyzed , the products of hydrolysis are either metabolized or secreted . the lactic acid generated by the hydrolytic degradation of pla becomes incorporated into the tricarboxylic acid cycle and is secreted as carbon dioxide and water . pga is also broken down by random hydrolysis accompanied by non - specific enzymatic hydrolysis to glycolic acid which is either secreted or enzymatically converted to other metabolized species . in another embodiment , the coating composition comprises a nonabsorbable polymer , such as ethylene vinyl acetate ( evac ), poly butyl methacrylate ( pbma ) and methylmethacrylate ( mma ) in amounts from about 0 . 5 to about 99 % of the final composition . the addition of evac , pbma or methylmethacrylate increases malleability of the matrix so that the device is more plastically deformable . the addition of methylmethacrylate to the coating delays the degradation of the coat and therefore , improves the controlled release of the coat , so that the pharmaceutical substance is released at a slower rate . the coating of the medical device can be applied to the medical device using standard techniques to cover the entire surface of the device or partially , as a single layer of a homogeneous mixture of drugs and matrix , and is applied in a thickness of from about 1 to 100 mm . alternative , multiple layers of the matrix / drug composition can be applied on the surface of the device . for example , multiple layers of various pharmaceutical substances can be deposited onto the surface of the medical device so that a particular drug can be released at one time , one drug in each layer , which can be separated by polymer matrix . the active ingredient or pharmaceutical substance component of the composition can range from about 1 to about 60 % ( w / w ) or the composition . upon contact of the coating composition with adjacent tissue where implanted , the coating begins to degrade in a controlled manner . as the coating degrades , the drug is slowly released into adjacent tissue and the drug is eluted from the device , thereby , preventing restenosis . additionally , since the polymers of the invention form a lattice of channels , the drugs are slowly released from the channels upon implantation of the device . therefore , the present invention provides an improved mechanism of delivering a drug to surrounding tissue from a coated medical device . that is , drug elution via channels in the coating matrix and degradation of the matrix . the coating of the invention can be made so that the drug provided can elute from the surface of the medical device for a period from the implant to about a year . the drug may elute by erosion as well as diffusion when drug concentrations are low . with high concentrations of drug , the drug may elute via channels in the coating matrix . the pharmaceutical substance of the invention includes drugs which are used in the treatment of restenosis . for example , the pharmaceutical substances include , but are not limited to antibiotics / antimicrobials , antiproliferatives , antineoplastics , antioxidants , endothelial cell growth factors , thrombin inhibitors , immunosuppressants , anti - platelet aggregation agents , collagen synthesis inhibitors , therapeutic antibodies , nitric oxide donors , antisense oligonucleotides , wound healing agents , therapeutic gene transfer constructs , peptides , proteins , extracellular matrix components , vasodialators , thrombolytics , anti - metabolites , growth factor agonists , antimitotics , steroidal and nonsterodial antiinflammatory agents , angiotensin converting enzyme ( ace ) inhibitors , free radical scavangers , anti - cancer chemotherapeutic agents . for example , some of the aforementioned pharmaceutical substances include , cyclosporins a ( csa ), rapamycin , mycophenolic acid ( mpa ), retinoic acid , vitamin e , probucol , l - arginine - l - glutamate , everolimus , and paclitaxel . the invention also relates to a method of treating a patient having vascular disease and in need of such treatment with the coated medical device of the invention . the method comprises administering to the patient a coated medical device of the invention . the following examples illustrate the invention , but in no way limit the scope of the invention . the polymer poly dl lactide - co - glycolide ( dlplg , birmingham polymers ) is provided as a pellet . to prepare the polymer matrix composition for coating a stent , the pellets are weighed and dissolved in a ketone or methylene chloride solvent to form a solution . the drug is dissolved in the same solvent and added to the polymer solution to the required concentration , thus forming a homogeneous coating solution . to improve the malleability and change the release kinetics of the coating matrix , the ratio of lactide to glycolide is varied . this solution is then used to coat the stent to form a uniform coating as shown in fig . 1 . alternatively , the polymer ( s )/ drug ( s ) composition can be deposited on the surface of the stent using standard methods . the polymer pellets of dlplg which have been dissolved in a solvent are mixed with one or more drugs . alternatively , one or more polymers can be dissolved with a solvent and one or more drugs can be added and mixed . the resultant mixture is applied to the stent uniformly using standard methods . after coating and drying , the stents are evaluated . the following list illustrates various examples of coating combinations , which were studied using various drugs and comprising dlplg and / or combinations thereof . in addition , the formulation can consist of a base coat of dlplg and a top coat of dlplg or another polymer such as dlpla or evac 25 . the abbreviations of the drugs and polymers used in the coatings are as follows : mpa is mycophenolic acid , ra is retinoic acid ; csa is cyclosporine a ; lov is lovastatin ™ ( mevinolin ); pct is paclitaxel ; pbma is poly butyl methacrylate , evac is ethylene vinyl acetate copolymer ; dlpla is poly ( dl lactide ), dlplg is poly ( dl lactide - co - glycolide ) examples of the coating components and amounts (%) which can be used in the invention comprise : 1 . 50 % mpa / 50 % poly l lactide 2 . 50 % mpa / 50 % poly dl lactide 3 . 50 % mpa / 50 % ( 86 : 14 poly dl lactide - co - caprolactone ) 4 . 50 % mpa / 50 % ( 85 : 15 poly dl lactide - co - glycolide ) 5 . 16 % pct / 84 % poly dl lacide 6 . 8 % pct / 92 % poly dl lactide 7 . 4 % pct / 92 % poly dl lactide 8 . 2 % pct / 92 % poly dl lactide 9 . 8 % pct / 92 % of ( 80 : 20 poly dl lactide / evac 40 ) 10 . 8 % pct / 92 % of ( 80 : 20 poly dl lactide / evac 25 ) 11 . 4 % pct / 96 % of ( 50 : 50 poly dl lactide / evac 25 ) 12 . 8 % pct / 92 % of ( 85 : 15 poly dl lactide - co - glycolide ) 13 . 4 % pct / 96 % of ( 50 : 50 poly dl lactide - co - glycolide ) 14 . 25 % lov / 25 % mpa / 50 % of ( evac 40 / pbma ) 15 . 50 % mpa / 50 % of ( evac 40 / pbma ) 16 . 8 % pct / 92 % of ( evac 40 / pbma ) 17 . 8 % pct / 92 % evac 40 18 . 8 % pct / 92 % evac 12 19 . 16 % pct / 84 % pbma 20 . 50 % csa / 50 % pbma 21 . 32 % csa / 68 % pbma 22 . 16 % csa / 84 % pbma the following experiments were conducted to measure the drug elution profile of the coating on stents coated by the method described in example 2 . the coating on the stent consisted of 4 % paclitaxel and 96 % of a 50 : 50 poly ( dl - lactide - co - glycolide ) polymer . each stent was coated with 500 μg of coating composition and incubated in 3 ml of bovine serum at 37 ° c . for 21 days . paclitaxel released into the serum was measured using standard techniques at various days during the incubation period . the results of the experiments are shown in fig2 . as shown in fig2 , the elution profile of paclitaxel release is very slow and controlled since only about 4 μg of paclitaxel are released from the stent in the 21 - day period . the following experiments were conducted to measure the drug elution profile of the coating on stents coated by the method describe in example 2 . the coating on the stent consisted of 4 % paclitaxel and 92 % of a 50 : 50 of poly ( dl - lactide ) and evac 25 polymer . each stent was coated with 500 μg of coating composition and incubated in 3 ml of bovine serum at 37 ° c . for 10 days . paclitaxel released into the serum was measured using standard techniques at various days during the incubation period . the results of the experiments are shown in fig3 . as shown in fig3 , the elution profile of paclitaxel release is very slow and controlled since only about 6 μg of paclitaxel are released from the stent in the 10 - day period . the following experiments were conducted to measure the drug elution profile of the coating on stents coated by the method describe in example 2 . the coating on the stent consisted of 8 % paclitaxel and 92 % of a 80 : 20 of poly ( dl - lactide ) and evac 25 polymer . each stent was coated with 500 μg of coating lactide ) composition and incubated in 3 ml of bovine serum at 37 ° c . for 14 days . paclitaxel released into the serum was measured using standard techniques at various days during the incubation period . the results of the experiments are shown in fig4 . as shown in fig4 , the elution profile of paclitaxel release is very slow and controlled since only about 4 μg of paclitaxel are released from the stent in the 14 - day period . the following experiments were conducted to measure the drug elution profile of the coating on stents coated by the method describe in example 2 . the coating on the stent consisted of 8 % paclitaxel and 92 % of poly ( dl - lactide ) polymer . each stent was coated with 500 μg of coating composition and incubated in 3 ml of bovine serum at 37 ° c . for 21 days . paclitaxel released into the serum was measured using standard techniques at various days during the incubation period . the results of the experiments are shown in fig5 . as shown in fig5 , the elution profile of paclitaxel release is very slow and controlled since only about 2 μg of paclitaxel are released from the stent in the 21 - day period . the above data show that by varying the polymer components of the coating , the release of a drug can be controlled for a period of time required .
a drug eluting medical device is provided for implanting into vessels or luminal structures within the body of a patient . the coated medical device , such as a stent , vascular , or synthetic graft comprises a coating consisting of a controlled - release matrix of a bioabsorbable , biocompatible , bioerodible , biodegradable , nontoxic material , such as a poly polymer , and at least one pharmaceutical substance , or bioactive agent incorporated within the matrix or layered within layers of matrix . in particular , the drug eluting medical device when implanted into a patient , delivers the drugs or bioactive agents within the matrix to adjacent tissues in a controlled and desired rate depending on the drug and site of implantation .