Rapamycin (Sirolimus) Side Effects: Withdrawal and Discontinuation Syndrome

What happens when sirolimus is stopped

The Rapamune label describes no withdrawal or discontinuation syndrome for sirolimus. What it documents is the set of reactions that led transplant patients to stop treatment: increased creatinine, hypertriglyceridemia and TTP each accounted for a discontinuation rate above 5% [1].

In the 48-week PEARL trial of healthy adults, adverse and serious adverse events were similar across the placebo, 5 mg weekly and 10 mg weekly groups [2]. For angioedema, the label notes that in some cases it resolved upon discontinuation or dose reduction of Rapamune [1].

How fast sirolimus leaves the body

Sirolimus is extensively metabolized in the intestinal wall and liver by CYP3A4 and is also a substrate of P-glycoprotein [1]. The label gives a mean terminal half-life of about 62 hours (SD 16) in stable renal transplant patients, with 91% of radioactivity recovered in feces [1]. That figure comes from transplant patients on maintenance therapy, not from healthy adults taking low weekly doses.

Half-life describes the decline in drug levels; it is not a countdown to zero. Using the label's average half-life of about 62 hours in stable kidney transplant patients, five half-lives works out to roughly 13 days. That is an estimate, not a measured stopping timeline [1].

Liver function changes exposure. Compared with normal liver function, sirolimus AUC is 43% higher in mild hepatic impairment, 94% higher in moderate and 189% higher in severe, and the label reduces the maintenance dose by about one third in mild-to-moderate impairment and one half in severe impairment [1]. Sirolimus is about 92% plasma protein bound, with a whole-blood to plasma ratio of 36 [1].

The label's taper instruction concerns cyclosporine

In low-to-moderate-risk kidney transplant recipients, cyclosporine is progressively discontinued over 4 to 8 weeks starting 2 to 4 months after transplant, and the Rapamune dose is adjusted to keep sirolimus whole-blood trough concentrations in the target range [1]. The label explains why the sirolimus dose has to be revisited at that point: cyclosporine inhibits sirolimus metabolism and transport, so sirolimus concentrations may fall when cyclosporine is withdrawn unless the Rapamune dose is increased [1].

Dose adjustment is guided by therapeutic drug monitoring, but the label says monitoring should not be the only basis for adjusting therapy — clinical signs and symptoms, biopsy findings and laboratory parameters also count [1].

What the transplant conversion data show

The CONVERT trial tested what happens when sirolimus replaces another drug. It enrolled 830 kidney transplant recipients 6 to 120 months after transplant and randomly assigned them to continue a calcineurin inhibitor (n=275) or convert to sirolimus (n=555) [4]. At 12 and 24 months, biopsy-confirmed acute rejection, graft survival and patient survival were similar between groups; urinary protein-to-creatinine ratios rose significantly after conversion, and malignancy rates were significantly lower [4]. Enrollment in the group with baseline GFR 20 to 40 mL/min was halted early because of more safety endpoints in the sirolimus arm [4].

The trial tested converting to sirolimus, not stopping it, so it does not measure what follows a last dose [4].

Low-dose weekly rapamycin in healthy older adults

PEARL was a 48-week double-blind, placebo-controlled trial in healthy, normative-aging adults who took 5 mg or 10 mg of compounded rapamycin once weekly [2]. Adverse and serious adverse events were similar across groups, and changes in blood biomarkers remained within normal ranges [2]. Visceral adiposity did not change significantly (p=0.942) [2]. Lean tissue mass and self-reported pain improved in women taking 10 mg, and emotional well-being and general health improved on 5 mg [2]. The authors concluded the drug was relatively safe over 48 weeks and that efficacy was not established [2].

Compounded rapamycin is not FDA-approved, and FDA does not verify the safety, effectiveness or quality of compounded drugs before they are marketed [5]. The label's approved uses are kidney transplant rejection prophylaxis in patients 13 and older and lymphangioleiomyomatosis; there is no approved indication for aging or longevity [1].

The pilot trial of 1 mg daily in adults aged 70 to 95 reported both symptoms and blood-count changes: one rapamycin participant had facial rash, one had stomatitis and two had gastrointestinal issues, and the rapamycin group also had significant decreases in hemoglobin, hematocrit, red cell count, RDW, MCV and MCH [3]. For context, in the label's renal transplant study — where every patient also received cyclosporine and corticosteroids — thrombocytopenia occurred in 14% of patients on 2 mg daily and 30% on 5 mg daily versus 9% on placebo, and anemia in 23% and 33% versus 21% [1].

Drugs that change sirolimus levels

Sirolimus is a substrate of both CYP3A4 and P-glycoprotein. Drugs that affect CYP3A4 and P-glycoprotein may lower or raise sirolimus blood levels [1]. The label says to avoid strong inducers such as rifampin and rifabutin and strong inhibitors such as ketoconazole, voriconazole, itraconazole, erythromycin, telithromycin and clarithromycin [1]. The label says grapefruit juice inhibits sirolimus metabolism and must not be taken with Rapamune or used to dilute it [1]. The cyclosporine interaction above is the one built into the labeled transplant regimen: withdrawing cyclosporine can lower sirolimus concentrations, and the Rapamune dose is adjusted to compensate [1].