Sirolimus and its analogues in the composition of intravascular stents
At the present time registration of medical devices containing pharmaceutical substances is the topic for discussion for many manufacturers, distributors and other participants of the medical device market (see the article About pharmaceutical agents in the composition of medical devices and registration difficulties). Difficulties in the registration connected with the changes of Russian regulation touched upon drug-eluting intravascular stents.
Stents capable of releasing pharmaceutical substances usually consist of the following elements:
- Metallic base
- Polymer layer
- Pharmaceutical substance
Sometimes one more polymer layer can be included to the composition of stent in order to prevent wash-out of the pharmaceutical substance.
What’s the use of drug-eluting stents?
Different pharmaceutical agents, for example, from the group of immunosupressors (sirolimus) can be useful in case of restenosis.
Restenosis is a narrowing of the blood vessel after angioplasty. The main factors taking part in the restenosis development are thrombosis and intimal hyperplasia.
During surgery endothelium becomes dehiscent and intimal tears appear. It leads to the damage of the middle vessel layer, aggregation of thrombocytes and development of thromb. Thromb is a «core» for the development of restenosis.
Smooth muscle cells of the vessel wall play the key role in the formation of restenosis. It is connected with their ability to migration, mitosis and synthesis of extracellular matrix when being stimulated. In the damaged vessel smooth muscle cells enter proliferation stage and move to the intima through the damaged internal elastic membrane (intimal hyperplasia) where extracellular matrix is intensively synthesized. As the result, the volume of extracellular matrix becomes a mass for the vessel narrowing.
In order to prevent intimal hyperplasia immunosupressors like Everolimus, Zotarolimus, Sirolimus and Tacrolimus can be used. This group of drugs causes antiproliferative effect and slows down cell devision (in this case, smooth muscle cells).
Sirolimus-eluting stents were implemented into practice for the first time in San Paulo (Brazil) and Rotterdam (The Netherlands). Forty-five patients were implanted stents with sirolimus coating (length – up to 18 mm). After 24 months there was no restenosis detected (0%) and itimal hyperplasia was minimal. (Sousa J.E., Costa M.A., Abizaid A.C., et al.)
In accordance with the above mentioned, we can conclude that drug-eluting stents can significantly improve patients’ condition after angioplasty.