Everolimus is an mTOR (mechanistic target of rapamycin) inhibitor used for immunosuppression in organ transplantation and for treatment of certain cancers, including renal cell carcinoma, breast cancer, and neuroendocrine tumors. Developed in the late 1990s and approved in the mid-2000s, everolimus works by inhibiting the mTOR pathway, which regulates cell growth, proliferation, and survival. Unlike abacavir, everolimus is not an antiviral, and its clinical use focuses on preventing organ rejection and slowing tumor progression. Its development included extensive clinical trials assessing dosing, efficacy, and safety, and it is available in oral tablet and dispersible tablet formulations for patient administration.
BRAND NAMES
Afinitor – primarily used for cancer treatment, including renal cell carcinoma, breast cancer, and neuroendocrine tumors.
Zortress / Certican – used for prevention of organ transplant rejection.
MECHANISM OF ACTION
Everolimus is an mTOR (mechanistic target of rapamycin) inhibitor that works by binding to the intracellular protein FKBP-12, forming a complex that inhibits mTORC1 (mTOR complex 1). This inhibition blocks downstream signaling pathways involved in cell growth, proliferation, angiogenesis, and metabolism.
PHARMACOKINETICS
Absorption
Everolimus is well absorbed orally, with peak plasma concentrations (C_max) typically reached 1–2 hours after ingestion. Its oral bioavailability is approximately 30%, and absorption can be enhanced when taken consistently with or without food, although high-fat meals may slightly reduce peak concentrations.
Distribution
Everolimus has an apparent volume of distribution (Vd) of approximately 100–150 L, indicating that it distributes extensively into body tissues beyond the plasma compartment.
Metabolism
Everolimus is extensively metabolized in the liver, primarily by the cytochrome P450 enzyme CYP3A4 and, to a lesser extent, by CYP3A5. It also undergoes glucuronidation via UDP-glucuronosyltransferases (UGTs). The metabolism produces inactive metabolites, which are subsequently excreted mainly in feces.
Elimination
Everolimus is eliminated primarily via hepatic metabolism, with less than 5% excreted unchanged in the urine. The majority of the drug and its inactive metabolites are excreted in feces. The terminal half-life of everolimus is approximately 30 hours, supporting once-daily oral dosing.
PHARMACODYNAMICS
Everolimus exerts its pharmacodynamic effects by inhibiting the mTORC1 signaling pathway, which regulates cell growth, proliferation, metabolism, and angiogenesis. In transplant patients, this leads to suppression of T-cell activation and proliferation, reducing the risk of organ rejection.
ADMINISTRATION
Everolimus is administered orally in the form of tablets or dispersible tablets. The drug is typically taken once daily at the same time each day, and it can be taken with or without food, although consistent timing is recommended to maintain steady plasma levels.
DOSAGE AND STRENGTH
Everolimus is available in tablet strengths of 2.5 mg, 5 mg, and 10 mg, with dosing tailored to the clinical indication. For oncology indications such as renal cell carcinoma, breast cancer, or neuroendocrine tumors, the usual dose is 10 mg orally once daily, with adjustments made based on tolerability and adverse effects.
DRUG INTERACTIONS
Everolimus is prone to multiple drug interactions due to its metabolism by CYP3A4 and transport via P-glycoprotein (P-gp). Co-administration with CYP3A4 or P-gp inhibitors such as ketoconazole, clarithromycin, or grapefruit juice can increase everolimus plasma levels, heightening the risk of toxicity, including liver dysfunction, infections, or stomatitis.
FOOD INTERACTIONS
Everolimus can be taken with or without food, but high-fat meals may reduce peak plasma concentrations (C_max) by up to 50% without significantly affecting overall exposure (AUC). For consistent drug absorption, it is recommended that patients take everolimus at the same time each day and consistently with respect to meals.
CONTRAINDICATIONS
Everolimus is contraindicated in patients with a known hypersensitivity to everolimus, sirolimus, or any component of the formulation. It should not be used in patients with severe hepatic impairment unless the benefits outweigh the risks, due to reduced metabolism and increased potential for toxicity.
SIDE EFFECTS
Hematologic:
Anemia
Leukopenia
Thrombocytopenia
OVER DOSAGE
Overdose of everolimus may exacerbate its known adverse effects, including stomatitis, hematologic abnormalities (anemia, leukopenia, thrombocytopenia), liver enzyme elevations, fatigue, and gastrointestinal disturbances.
TOXICITY
Everolimus exhibits toxicity primarily through its effects on hematologic, gastrointestinal, hepatic, and pulmonary systems. The most common toxicities include stomatitis, anemia, leukopenia, thrombocytopenia, elevated liver enzymes, hyperlipidemia, and fatigue. Rare but serious toxicities include non-infectious pneumonitis and severe infections due to immunosuppression.
