What are drug-eluting stents and how do they work?

During coronary angioplasty, coronary plaques are compressed against the arterial wall by the angioplasty balloon. To maintain the result of the opened lumen and to prevent the closure of the lumen by fragmented/ dissected plaques, stents, which are tubular metallic scaffolding tubes, are usually placed in the coronary arteries. In most patients, the stented vessel lumen will remain patent. However, in 20-30% of patients, restenosis inside the stented segment may occur due to the growth of neointimal tissues, as a natural response to injury, from the endothelium. In drug eluting stents, there is a coating on the surface of the stent struts which contains some drugs that can inhibit the growth of these neointimal tissues. By controlled release of the drugs onto the endothelial surface, the restenosis process will be controlled or inhibited.

Back to top

What is their efficacy and how safe are them?

With drug-eluting stents, the restenosis rate may be lowered to 5-10%, depending on the size and length of the diseased segments. They, therefore, will greatly reduce the need for a repeated procedure. However, comparing with bare metal stents, there may be a slight increase in late thrombosis rate, up to 0.2% per year.

Back to top

Conventionally, after the procedure of drug-eluting stent implantation, patients would be put on dual anti-platelet therapy with aspirin and clopidogrel for at least 3 to 6 months, depending on the type of drug-eluting stents used. After this period, life long single anti-platelet therapy with either one of the above two drugs is needed. In view of the mild increase in late thrombosis rate, a science advisory paper from American Heart Association and American College of Cardiology was issued in January this year and it stated that a longer initial period of dual anti-platelet therapy for 12 months is recommended. It also recommends postponing elective surgery for 1 year and if surgery cannot be deferred, considering the continuation of aspirin during the perioperative period in high risk patients with drug eluting stents.

Figure 1: Cross-section of coronary artery immediately after implantation of a bare metal stent.

Figure 2: Cross-section of coronary artery showing signifi cant in-stent restenosis 6 months after the implantation of a bare metal stent.

Figure 3: Picture on the left shows moderate in-stent restenosis after bare metal stent and the picture on the right shows much less in-stent restenosis after drug eluting stent.

Back to top

What is the diagnosis?

The diagnosis is pitted keratolysis.

Back to top

What is the causative agent?

It is a superfi cial infection of the stratum corneum characterized by shallow, punched-out, circular erosions mainly over the forefoot or sole or both. It is caused by several species of Corynebacterium, Dermatophilus, Actinomyces, and Micrococcus. The bacteria produce proteinases that destroy the startum corneum, causing pits. The malodor is due to production of sulfur-compound by-products, such as thiols, sulfi des and thioesters. It is usually asymptomatic but there may be soreness or itch.

Back to top

Is laboratory investigation required to confirm the diagnosis?

The diagnosis is made by a combination of clinical features and characteristic cheesy malodor. In doubtful cases, skin scraping for fungi helps to exclude tinea pedis.

Back to top

What are the predisposing factors?

The predisposing factors include heat, humidity, prolonged occlusion, hyperhidrosis and increased skin surface pH.

Back to top

What are the treatments?

Any predisposing factors should be corrected. These include avoiding occlusive footwear, reduction of foot friction, using absorbent cotton socks, wearing open toed sandals, washing feet twice a day and avoid sharing of footwear and towels. Pitted keratolysis can be treated with topical antibiotics such as fusidic acid, erythromycin, clindamycin, mupirocin, clotrimazole and miconazole. It also responds to oral erythromycin. Antiperspirant should be applied if there is hyperhidrosis. The prognosis is excellent.

Back to top