Exemestane is an aromatase inhibitor used primarily for the treatment of hormone receptor–positive breast cancer in postmenopausal women. Developed in the 1990s and approved in the early 2000s, exemestane works by irreversibly inhibiting thearomatase enzyme, which converts androgens into estrogens. Unlike abacavir, exemestane is not an antiviral; its clinical use is focused on oncology. It is available in oral tablet form and is often used as adjuvant therapy following surgery or in combination with other hormonal treatments to reduce cancer recurrence.
BRAND NAMES
Aromasin – the most widely recognized original brand name
Exemestane Tablets – generic or descriptive labeling used in many countries.
MECHANISM OF ACTION
Exemestane works by irreversibly inhibiting the aromatase enzyme, which is responsible for converting androgens into estrogens in postmenopausal women. By lowering circulating estrogen levels, exemestane reduces stimulation of estrogen receptor–positive breast cancer cells, thereby slowing or halting tumor growth.
PHARMACOKINETICS
Absorption
Exemestane is rapidly absorbed after oral administration, with peak plasma concentrations (C_max) reached within 2 hours. Its absolute bioavailability is approximately 42%, and absorption is not significantly affected by food, allowing it to be taken with or without meals.
Distribution
Exemestane has a moderate apparent volume of distribution (Vd) of approximately 160 L, indicating that the drug distributes beyond the plasma into body tissues.
Metabolism
Exemestane is extensively metabolized in the liver, primarily by cytochrome P450 enzymes, especially CYP3A4, and through reduction and subsequent conjugation (glucuronidation and sulfation). The metabolism produces inactive metabolites, which are then excreted mainly in urine and feces.
Elimination
Exemestane is eliminated primarily via hepatic metabolism, with only a small fraction (<1%) excreted unchanged in the urine. Its metabolites are excreted through both urine and feces, reflecting extensive biotransformation. The terminal half-life is approximately 24 hours, supporting once-daily oral dosing.
PHARMACODYNAMICS
Exemestane exerts its pharmacodynamic effect by irreversibly inhibiting the aromatase enzyme, which is responsible for converting androgens into estrogens in postmenopausal women. This suppression of estrogen synthesis decreases circulating estrogen levels, thereby reducing stimulation of estrogen receptor–positive breast cancer cells.
ADMINISTRATION
Exemestane is administered orally in the form of 25 mg tablets. It is typically taken once daily, preferably after a meal to enhance absorption, though it can be taken with or without food.
DOSAGE AND STRENGTH
Exemestane is available in 25 mg oral tablets, which is the standard and recommended strength for all approved indications. The typical dosage is 25 mg once daily, taken after a meal for optimal absorption. This regimen is used for adjuvant treatment of hormone receptor–positive breast cancer in postmenopausal women and for advanced or metastatic breast cancer when indicated.
DRUG INTERACTIONS
Exemestane is subject to significant drug interactions due to its metabolism primarily via CYP3A4. Co-administration with CYP3A4 inhibitors such as ketoconazole, itraconazole, or clarithromycin can increase plasma levels of exemestane, heightening the risk of adverse effects like fatigue, hot flashes, or liver enzyme elevations.
FOOD INTERACTIONS
Exemestane can be taken with or without food, but it is preferable to take it after a meal to enhance absorption and maintain consistent plasma levels. Food does not significantly affect overall bioavailability (AUC), although high-fat meals may slightly alter peak concentrations (C_max).
CONTRAINDICATIONS
Exemestane is contraindicated in patients with a known hypersensitivity to exemestane or any component of the formulation. It should not be used in premenopausal women who have functioning ovaries, as its efficacy depends on postmenopausal estrogen levels.
SIDE EFFECTS
Arthralgia (joint pain)
Myalgia (muscle pain)
Osteoporosis and increased fracture risk
Hot flashes
Sweating
Vaginal dryness
Nausea and vomiting
Indigestion
Diarrhea.
OVER DOSAGE
Overdose of exemestane may exacerbate its common adverse effects, including hot flashes, fatigue, nausea, vomiting, joint and muscle pain, and liver enzyme elevations. There isno specific antidotefor exemestane overdose, so management is mainly supportive.
TOXICITY
Exemestane exhibits toxicity primarily through its estrogen-lowering effects, which can impact multiple organ systems. Common toxicities include musculoskeletal effects such as arthralgia, myalgia, and osteoporosis, as well as menopausal symptoms like hot flashes, sweating, and vaginal dryness. Gastrointestinal effects such as nausea, vomiting, and diarrhea may occur,10 along with fatigue, weight gain, and hypercholesterolemia.
