Drug coated balloons (DCBs) appeared in the European market of interventional cardiology in 2007, with the aim of offering a combined therapeutic, mechanical (linked to balloon dilatation) and biological (ensured by drug release in the vessel wall) solution, furthermore, avoiding the implantation of a permanent prosthesis [1].

Nowadays, drug-eluting stents (DES) are considered the treatment of choice for percutaneous coronary revascularization but their use still presents certain limitations, including in particular anatomical settings, such as small vessels or bifurcations, and these limitations relate to clinical conditions, such as increased bleeding or thrombotic risk [2]. To overcome some of these limitations, DCBs have been developed in recent years [1,3]. DCBs are balloons with a variable degree of compliance, coated with an antiproliferative drug that is rapidly released upon contact with the wall. DCBs are designed to deliver an antiproliferative drug and not to treat the stenosis. Therefore, before their use, the lesion must be adequately pre-treated and the device is then inflated for a long time (30–120 s), which allows an adequate transfer of the drug to the vessel wall [3].

DCBs offer some theoretical advantages over DES. One of the advantages of DCBs compared to DES is that they provide a larger contact surface with the vessel, allowing a more homogeneous drug–tissue transfer. Moreover, the lack of a permanent prosthesis in the vessel favors the restoration of regular vasomotion and the possibility of reducing the duration of the dual antiplatelet therapy. In this way, the mechanical expansion of the vessel is combined with the release of an antiproliferative drug, which begins its journey inside the vascular wall from the intima to the media and adventitia: in these last two locations, in fact, the drug will promote a physiological healing of the vessel with a positive remodeling and potential lumen gain [4].

In addition to the ‘local’ benefits for the treated lesion, different trials and meta-analyses [5,6,7,8] have underlined a trend for better clinical outcomes and reduced all-cause mortality with DCBs as compared to DES, although these findings and the exact pathophysiological basis for this observation still deserve further investigation [4].

The most widely studied drug in the setting of DCBs is paclitaxel, whose physicochemical properties seem to make the substance most suitable for this application [9]. Different paclitaxel formulations have been used, including drug-only coatings as well as combinations with small fractions (typically 10%) of different additives, such as iopromide, urea, butyryl trihexyl citrate or a combination of polysorbate and sorbitol. Paclitaxel is a lipophilic drug that rapidly crosses the cell membrane of smooth muscle cells and binds to microtubules, stabilizing them during mitosis, thus inhibiting cell division and migration, and therefore, cell proliferation [10]. The dosage range is between 2 and 3.5 μg/mm² of inflated balloon surface. The coating (matrix or carrier) of the balloon is essential because it must be able to retain the drug during the transit of the lesion and ensure a rapid and homogeneous transfer to the vessel wall during inflation, reducing the risk of dispersion. Paclitaxel is typically applied into the balloon surface at a concentration of 3 mg/mm². Each type of paclitaxel-coated balloon (pDCB) is characterized by a different drug/excipient system, because if paclitaxel is applied as a firm compound, the required bioavailability is not obtained, as demonstrated in studies on porcine coronary overstretch models [11]. DCBs coated with paclitaxel in a water-soluble matrix have shown beneficial effects in the treatment and prevention of restenosis in the porcine and in humans, for both coronary in-stent restenosis and in peripheral arteries [12,13]. DCBs based on the Paccocath^® technology (SeQuent Please) is widely available: in this case, the balloon is coated with a homogenous matrix of paclitaxel and contrast media (iopromide). This last drug acts as a ‘spacer’ and, thereby, makes the coating porous and paclitaxel bioavailable. Therefore, the matrix allows a reliable release and enables an immediate uptake into the vascular wall of paclitaxel. The hydrophilic character of iopromide and the lipophilic properties of paclitaxel support the release of the drug from the balloon surface and its delivery into the vascular wall. The Paccocath^® technology has long term efficacy with a short term exposure: after a ‘single shot’ application of paclitaxel, there is a sustained antiproliferative action on smooth muscle cells over 14 days in absence of cytotoxic effects. Following such single drug delivery, the paclitaxel concentration reaches bottom levels in vascular cells after 24 h [14]. However, other additives or strategies to release the antiproliferative drug have been tested; for example, the Dior balloon has a ‘nanoporous’ balloon surface containing paclitaxel microcrystals following dimethyl sulfoxide treatment [15]. Commercially available DCBs’ characteristics are summarized in Table 1 together with the references of the most important studies [6,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56].

Although paclitaxel presents the most robust data for PTCA balloon coating, ‘limus’-eluting stents are currently dominating the scenario of coronary interventions for drug eluting stents. The benefit of sirolimus (or the ‘limus’ group) as an anti-proliferative drug, as compared to paclitaxel, has been documented in several DES trials [57,58,59]. Its main benefits include the cytostatic mode of action (compared to the cytotoxic effect of paclitaxel) and increased anti-restenotic effect. Moreover, sirolimus, compared to paclitaxel, has a lower lipophilicity but a wider therapeutic window. For stent-based local drug delivery, sirolimus must be released for a period of several weeks to achieve effective inhibition of neointimal proliferation. Preclinical studies have demonstrated the feasibility of sirolimus balloon coating in a dose range of 1 to 7 μg per mm² balloon surface, with varying amorphous or crystalline formulations [60].

It was commonly thought that only sustained drug release would ensure persistent prevention of restenosis after angioplasty and stent implantation [61]. Considering that the inhibition of neointimal proliferation by sirolimus-coated balloons (sDCBs) in the porcine model was similar to the corresponding effect of sirolimus-eluting stents, a possible clinical indication for sirolimus-coated balloons was suggested to be drug-eluting stent restenosis [60]. In 2016, the first sirolimus-coated DCB (MagicTouch) obtained the CE mark. The technology designed for this device consists of the entrapment of sirolimus in a protective lipophilic package, which allows diffusion and penetration into the arterial wall during balloon inflation, overcoming the low lipophilicity of sirolimus. The package is composed of nanospheres of 100–300 nm in diameter. The total drug dosage corresponds to 1.25 mg/mm² of balloon surface area (within the therapeutic window of sirolimus). In a prospective, multicenter clinical registry, MagicTouch sDCBs showed good immediate performance and an adequate and encouraging safety profile at 12 months [6].

In 2019, a study on the treatment of coronary DES restenosis by sDCBs showed similar efficacy in terms of late lumen loss (LLL) as compared to the SeQuent Please pDCB [62].

A subsequent indirect comparison between pDCB and sDCB found no significant difference in clinical endpoints at 12-month follow-up (p = 0.89 for MACE) [63], and this result was then confirmed by randomized clinical trials. Recently, in fact, sDCB proved to be non-inferior to pDCB in regards to LLL, either in in-stent restenosis (lumen loss in-segment at 6 months; mean difference between sDCB and pDCB 0.01–95% CI: −0.23 to 0.24; non-inferiority at a predefined margin of 0.35 shown [64]) or in de novo lesions (lumen loss at 6 months; mean difference 0.08–95% CI: −0.07 to 0.24, although negative lumen loss was more frequent in the pDCB group (60% vs. 32% of lesions; p = 0.019) [16]. However, these studies did not show any difference in clinical events [16,64]. Commercially available DCBs’ characteristics are summarized in Table 1.