Clinical Use: Sirolimus is an immunosuppressive drug that is used in patients who have undergone organ transplants, particularly kidney.
Background: Sirolimus is a compound produced by the bacteria Streptomyces hygroscopicus. Sirolimus inhibits the response to interleukin-2 (IL-2) and thereby blocks activation of T- and B-cells. In contrast, tacrolimus inhibits the production of IL-2. Sirolimus limits the immune response and helps to prevent organ rejection by inhibiting immune cell activation and proliferation, and antibody production.

The chief advantage sirolimus has over calcineurin inhibitors is that it has low renal toxicity. 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 sirolimus 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.

Sirolimus can be taken orally and it is absorbed from the gastrointestinal tract, concentrations peak in the blood within 1 – 2 hours of being taken and then gradually decline. Sirolimus concentrations in the blood must be maintained with a narrow range. If the concentration is too low, organ rejection may occur; if it is too high, then the patient may suffer from toxicity. Dosages must be tailored to the individual and closely monitored.

The anti-proliferative effect of sirolimus has also been used in conjunction with coronary stents to prevent restenosis in coronary arteries following balloon angioplasty. Additionally sirolimus is currently being assessed as a therapeutic option for autosomal dominant polycystic kidney disease (ADPKD). Case reports indicate that sirolimus can reduce kidney volume and delay the loss of renal function in patients with ADPKD.

Reference Ranges: Initial target 4.0 – 12.0 ng/ml
Associated Diseases:
Patient Preparation: None required
Specimen Requirements: EDTA – Whole blood sample
Turnaround Time: 1 week
Additional Information: Also known as Rapamycin & Rapamune.
Referred Test: Referred test
Location: Freeman Hospital