ACVIM General Boards Practice Test 2026 – Comprehensive Exam Preparation

Sirolimus is a drug that specifically targets the mammalian target of rapamycin (mTOR) pathway, a critical regulator of cell growth, proliferation, and survival. This pathway plays a significant role in various biological processes, including the response to nutrient availability and growth factor signaling. Sirolimus, also known as rapamycin, functions as an immunosuppressant primarily used in transplant patients to prevent organ rejection. By inhibiting mTOR, it is effective at modulating the immune response without the cytotoxic effects associated with many traditional immunosuppressants.

In contrast, the other drugs listed—cyclophosphamide, prednisone, and azathioprine—do not specifically inhibit the mTOR pathway. Cyclophosphamide is an alkylating agent that interferes with DNA synthesis and is used primarily for its cytotoxic effects on rapidly dividing cells. Prednisone is a corticosteroid that exerts anti-inflammatory and immunosuppressive effects through various mechanisms, including glucocorticoid receptor activation but not directly on the mTOR pathway. Azathioprine is a purine synthesis inhibitor that also impacts cell proliferation but again does not target mTOR specifically. Thus, sirolimus stands out as the specific agent that directly