Rapamycin & Proteinuria

Rapamycin (sirolimus) is a commonly used immunosupressant deriving from the bacterium Streptomyces hygroscopicus, originally found on Easter Island. It was originally developed as an antifungal agent but later found to have potent immunosuppressive and antiproliferative properties.

Although effective, rapamycin has a number of unpleasant side effects, including poor wound healing (therefore it generally is not used in the immediate post-transplant period), oral ulcers, pneumonitis, pleural & pericardial effusions, bone marrow suppression (especially thrombocytopenia), GI effects, and, interestingly, proteinuria.

Rapamycin appears to cause proteinuria, often in the nephrotic range, and the lesion appears to be focal segmental glomerulosclerosis (FSGS), according to this 2007 CJASN article by a French group.