A 31-year-old female receives a kidney transplant for autosomal dominant polycystic kidney disease (ADPKD). Three weeks later, the patient experiences acute, T-cell mediated rejection of the allograft and is given sirolimus. Which of the following are side effects of this medication?

Hyperlipidemia, thrombocytopenia

Nephrotoxicity, gingival hyperplasia

Cytokine release syndrome, hypersensitivity reaction

A patient with HCC and a long history of alcohol dependence and chronic hepatitis C has been using the mTOR inhibitor sirolimus 100 mg for cancer treatment. Her cancer has shown a partial response. She also has a history of hypertension and poorly controlled type 2 diabetes mellitus complicated by diabetic retinopathy. Current medications include enalapril and insulin. She asks her oncologist and hepatologist if she could try everolimus for its purported survival benefit in treating HCC. Based on clinical considerations, which of the following statements is most accurate?

The patient is not a good candidate for everolimus due to her history of diabetes

The patient should start everolimus 50 mg because of the survival benefit relative to sirolimus 100 mg

The patient is not a good candidate for everolimus due to her history of hypertension

The patient should start everolimus 100 mg because of the survival benefit relative to sirolimus 100 mg

The patient should start everolimus 50 mg because of her history of alcohol use disorder and hepatitis C

A 53-year-old man with hyperlipidemia comes to the physician for a follow-up examination. His home medications include acetaminophen and atorvastatin. Serum studies show elevated total cholesterol and triglyceride concentrations. A drug that activates the peroxisome proliferator-activated receptor alpha is added to his existing therapy. This patient is at highest risk for developing which of the following drug-related adverse effects?

Reddish-brown discoloration of urine

Acutely swollen and painful joint

Pruritus and flushing of the skin

A 53-year-old woman with hypertension and hyperlipidemia comes to the physician because of generalized reddening of her skin and itching for the past 2 weeks. Her symptoms occur every evening before bedtime and last for about 30 minutes. Three months ago, atorvastatin was stopped after she experienced progressively worsening neck and back pain. Statin therapy was reinitiated at lower doses 3 weeks ago but had to be stopped again after her musculoskeletal symptoms recurred. Her menses occur irregularly at 2–3 month intervals and last for 3–4 days. She has smoked one pack of cigarettes daily for the past 30 years. Her current medications include lisinopril and niacin. Her brother died of colonic adenocarcinoma, and her father died of small cell lung cancer. She is 169 cm (5 ft 6 in) tall and weighs 83 kg (183 lb); BMI is 29 kg/m2. Her vital signs are within normal limits. Physical examination shows no abnormalities. Serum lipid studies show: Total cholesterol 247 mg/dL HDL-cholesterol 39 mg/dL LDL-cholesterol 172 mg/dL Triglycerides 152 mg/dL Which of the following is the most appropriate next step in management?

Switch lisinopril to hydrochlorothiazide

Measure urine hydroxyindoleacetic acid levels

Measure urine metanephrine levels

A 24-year-old woman presents to the emergency department because she started experiencing dyspnea and urticaria after dinner. Her symptoms began approximately 15 minutes after eating a new type of shellfish that she has never had before. On physical exam her breathing is labored, and pulmonary auscultation reveals wheezing bilaterally. Given this presentation, she is immediately started on intramuscular epinephrine for treatment of her symptoms. If part of this patient's symptoms were related to the systemic release of certain complement components, which of the following is another function of the responsible component?

Inhibition of kallikrein activation

mTOR inhibitors for USMLE Step 2 CK: High-Yield Pharmacology Lessons

Mechanism of Action - The Cell Cycle Brake

Primary Target: Mammalian Target of Rapamycin (mTOR), a key serine/threonine kinase.
Action: Sirolimus (Rapamycin) and Everolimus first bind to the intracellular protein FKBP-12.
- This drug-immunophilin complex then binds to and inhibits mTOR.
Cellular Effect: Inhibition of mTOR blocks the signal transduction pathway downstream of the IL-2 receptor, arresting the cell cycle at the G1-S phase.
- This prevents the proliferation of T-lymphocytes.

⭐ Exam Pearl: Unlike calcineurin inhibitors (Tacrolimus, Cyclosporine) which prevent IL-2 synthesis, mTOR inhibitors block the T-cell's response to IL-2 stimulation.

The Drugs & PK - Rapa's Crew

Sirolimus (Rapamycin)
- The original macrolide mTOR inhibitor, isolated from the bacterium Streptomyces hygroscopicus.
- PK: Administered orally; has a long half-life of approx. 60 hours.
Everolimus
- A derivative of sirolimus (a "limus" drug).
- PK: Shorter half-life (~30 hours) and improved oral bioavailability compared to sirolimus.
Temsirolimus
- A prodrug that is converted to sirolimus.
- PK: Administered IV.
Zotarolimus
- A sirolimus analog developed for specific applications.
- PK: Primarily used in drug-eluting stents.

⭐ Sirolimus and its analogs are famously used in drug-eluting stents (DES) to inhibit smooth muscle cell proliferation, thereby preventing coronary artery restenosis following angioplasty.

Clinical Uses - Stents & Transplants

Drug-Eluting Stents (DES)
- Sirolimus and everolimus are coated on coronary stents.
- Action: Block local T-cell proliferation and smooth muscle cell migration.
- Purpose: Prevents in-stent restenosis after percutaneous coronary intervention (PCI).
Solid Organ Transplant Rejection
- Prophylaxis for kidney, liver, & heart transplant rejection.
- Often used in combination with corticosteroids and calcineurin inhibitors, or as a CNI-sparing agent.

⭐ Kidney-Sparing Effect: mTOR inhibitors are valuable in renal transplant patients with calcineurin inhibitor (e.g., tacrolimus) induced nephrotoxicity, allowing for CNI dose reduction.

Adverse Effects - SIR‑ious Side Effects

📌 Mnemonic: SIR-ious side effects.

Stomatitis: Painful mouth ulcers and mucositis.
Insulin resistance: Resulting in hyperglycemia and new-onset diabetes.
Rash: Acneiform skin eruptions are common.
Pancytopenia: Dose-related myelosuppression affecting all cell lines (anemia, thrombocytopenia, leukopenia).
Hyperlipidemia: Significant increases in both cholesterol and triglycerides.
Impaired wound healing: Due to anti-proliferative effects; caution post-surgery.
Nephrotoxicity: Potentiates kidney damage from calcineurin inhibitors.

⭐ A key, potentially severe toxicity is non-infectious interstitial pneumonitis. It presents with cough and dyspnea, is dose-dependent, and often reversible upon drug cessation.

High‑Yield Points - ⚡ Biggest Takeaways

Sirolimus (Rapamycin) and Everolimus inhibit mTOR by binding to FKBP, which blocks IL-2 signal transduction and halts G1-S phase progression.

Primarily used for prophylaxis of solid organ rejection, especially in kidney transplants, and within drug-eluting stents.

Major adverse effects include pancytopenia, dose-dependent hyperlipidemia (especially ↑ triglycerides), and insulin resistance.

Crucially, unlike calcineurin inhibitors, mTOR inhibitors are not nephrotoxic.

Metabolized by CYP3A4, creating a high potential for drug-drug interactions.

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mTOR inhibitors