Atherosclerosis is a syndrome affecting arterial blood vessels. It leads to a chronic inflammatory response in the walls of arteries, which is in large part due to the accumulation of lipid, macrophages, foam cells and the formation of plaque in the arterial wall. Atherosclerosis is commonly referred to as hardening of the arteries although the pathophysiology of the disease manifests itself with several different types of lesions ranging from fibrotic to lipid laden to calcific. Angioplasty is a vascular interventional technique involving mechanically widening an obstructed blood vessel, typically caused by atherosclerosis.
During angioplasty, a catheter having a tightly folded balloon is inserted into the vasculature of the patient and is passed to the narrowed location of the blood vessel at which point the balloon is inflated to a fixed size using an inflation fluid, typically a solution of angiographic contrast media. Percutaneous coronary intervention (PCI), commonly known as coronary angioplasty, is a therapeutic procedure to treat the stenotic coronary arteries of the heart, often found in coronary heart disease.
In contrast, peripheral angioplasty, commonly known as percutaneous transluminal angioplasty (PTA), refers to the use of mechanical widening of blood vessels other than the coronary arteries. PTA is most commonly used to treat narrowing of the arteries of the leg, especially, the iliac, external iliac, superficial femoral and popliteal arteries. PTA can also treat narrowing of veins and other blood vessels.
It was determined that following angioplasty, although a blood vessel would be successfully widened, sometimes the treated wall of the blood vessel experienced abrupt closure after balloon inflation or dilatation, due to acute recoil or spasm. Interventional cardiologists addressed this problem by stenting the blood vessel to prevent acute recoil and vasospasm. A stent is a device, typically a metal tube or scaffold, which was inserted into the blood vessel following angioplasty, in order to hold the blood vessel open.
While the advent of stents eliminated many of the complications of abrupt vessel closure after angioplasty procedures, within about six months of stenting, a re-narrowing of the blood vessel can form, which is a condition known as restenosis. Restenosis was discovered to be a response to the injury of the angioplasty procedure and is characterized by a growth of smooth muscle cells—analogous to a scar forming over an injury. As a solution, drug eluting stents were developed to address the reoccurrence of the narrowing of blood vessels. One example of a drug eluting stent is a metal stent that has been coated with a drug that is known to interfere with the process of restenosis. A potential drawback of certain drug eluting stents is known as late stent thrombosis, which is an event in which blood clots form inside the stent.
Drug coated balloons are believed to be a viable alternative to drug eluting stents in the treatment of atherosclerosis. In a study which evaluated restenosis, and the rate of major adverse cardiac events such as heart attack, bypass, repeat stenosis, or death in patients treated with drug coated balloons and drug eluting stents, the patients treated with drug coated balloons experienced only 3.7 percent restenosis and 4.8% MACE as compared to patients treated with drug eluting stents, in which restenosis was 20.8 percent and 22.0 percent MACE rate. (See, PEPCAD II study, Rotenburg, Germany).
Although drug coated balloons are a viable alternative and in some cases may have greater efficacy than drug eluting stents as suggested by the PEPCAD II study, drug coated balloons present challenges due to the very short period of contact between the drug coated balloon surface and the blood vessel wall. The drug delivery time period for a drug coated balloon differs from that of a controlled release drug eluting stent, which is typically weeks to months. In particular for the coronary arteries, the balloon may only be inflated for less than one minute, and is often inflated for only thirty seconds. Therefore, an efficacious, therapeutic amount of drug must be transferred to the vessel wall within a thirty-second to one-minute time period. For the peripheral vasculature, the allowable inflation times can be greater than one minute, but are still measured in minutes. Thus, there are challenges specific to drug delivery via a drug coated balloon because of the necessity of a short inflation time, and therefore time for drug or coating transfer—a challenge not presented by a drug eluting stent, which remains in the patient's vasculature once implanted.
Various embodiments of drug-coated balloons have been proposed to address these needs, including balloons with a therapeutic agent disposed directly on the balloon surface and balloons having various protective sheaths. However, not all embodiments result in an efficacious response in reducing restenosis after balloon and/or bare metal stent trauma.
Furthermore, it is desirable to retain the drug on the vessel wall after balloon inflation and release of the coating to the site of delivery. Tissue retention will depend on several factors, including characteristics of the therapeutic agent and the formulation of the balloon coating. Such retention will permit greater local drug uptake, thereby improving treatment efficacy and decreasing systemic exposure to the therapeutic agent.
Thus, there remains a need for, and an aim of the disclosed subject matter is directed towards, coating compositions and corresponding methods for drug delivery balloons that permit enhanced retention of the coating at the site of delivery by chemical modification of the coating at the delivery site.