Rapamycin in Clinical uses

Rapamycin, also known as sirolimus, is an immunosuppressant drug used to prevent rejection in organ transplantation; it is especially useful in kidney transplants. It prevents activation of T cells and B cells by inhibiting their response to interleukin-2. Rapamycin is also used as a coronary stent coating.

Rapamycin was originally developed as an antifungal agent. However, this use was abandoned when it was discovered to have potent immunosuppressive and antiproliferative properties. It has since been shown to prolong the life of mice and might also be useful in the treatment of certain cancers.

Here are the two Clinical uses of Rapamycin:

 1.Prevention of transplant rejection

The chief advantage Rapamycin has over calcineurin inhibitors is its low toxicity towards kidneys. Transplant patients maintained on calcineurin inhibitors long-term tend to develop impaired kidney function or even chronic renal failure; this can be avoided by using Rapamycin instead. It is particularly advantageous in patients with kidney transplants for hemolytic-uremic syndrome, as this disease is likely to recur in the transplanted kidney if a calcineurin-inhibitor is used. However, on October 7, 2008, the FDA approved safety labeling revisions for Rapamycin to warn of the risk for decreased renal function associated with its use.

Rapamycin can also be used alone, or in conjunction with calcineurin inhibitors, such as tacrolimus and/or mycophenolate mofetil, to provide steroid-free immunosuppression regimens. Impaired wound healing and thrombocytopenia are a possible side effects of Rapamycin; therefore, some transplant centres prefer not to use it immediately after the transplant operation, but instead administer it only after a period of weeks or months. Its optimal role in immunosuppression has not yet been determined, and is the subject of a number of ongoing clinical trials.

Rapamycin is absorbed into the blood stream from the intestine variably in each patient, with some patients having up to eight times more exposure than others for the same dose. Drug levels are therefore taken to make sure patients get the right dose for their condition. This is determined by taking a blood sample before the next dose which gives the trough level. Fortunately, there is good correlation between trough concentration levels and drug exposure, known as area under the concentration-time curve, for both Rapamycin (SRL) and tacrolimus (TAC) (SRL: r2 = 0.83; TAC: r2 = 0.82), so only one level need be taken to know its pharmacokinetic (PK) profile. PK profiles of SRL and of TAC are unaltered by simultaneous administration. Dose-corrected drug exposure of TAC correlates with SRL (r2 = 0.8), so patients have similar bioavailability of both.

2.Coronary stent coating

The antiproliferative effect of Rapamycin has also been used in conjunction with coronary stents to prevent restenosis in coronary arteries following balloon angioplasty. The Rapamycin is formulated in a polymer coating that affords controlled release through the healing period following coronary intervention. Several large clinical studies have demonstrated lower restenosis rates in patients treated with Rapamycin-eluting stents when compared to bare metal stents, resulting in fewer repeat procedures. A Rapamycin-eluting coronary stent was marketed by Cordis, a division of Johnson & Johnson, under the tradename Cypher. It has been proposed, however, that such stents may increase the risk of vascular thrombosis.

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