Exemestane is a steroidal, irreversible, third-generation aromatase inhibitor used primarily in the adjuvant treatment of hormone receptor-positive early and advanced breast cancer in postmenopausal women. It acts as a 'suicide inhibitor' of the aromatase enzyme, permanently deactivating it and leading to a profound reduction in circulating estrogen levels, which is crucial for suppressing the growth of estrogen-dependent tumors.
Adult: 25 mg once daily, orally, after a meal (preferably after breakfast or the main meal).
Note: Tablet should be swallowed whole with water, after a meal to improve gastrointestinal tolerance and bioavailability. Therapy should be continuous. If a dose is missed, it should be taken as soon as remembered unless it is almost time for the next dose. Do not double the dose.
Exemestane is an irreversible, steroidal aromatase inactivator. It mimics the natural substrate androstenedione and binds irreversibly to the substrate-binding site of the aromatase enzyme (CYP19A1). This covalent binding causes permanent inactivation of the enzyme, blocking the conversion of androgens (androstenedione and testosterone) to estrogens (estrone and estradiol) in peripheral tissues (adipose, muscle, liver, breast) and in cancer tissue itself.
Pregnancy: Pregnancy Category D (US FDA). Contraindicated. Can cause fetal harm based on mechanism of action (estrogen deprivation). Exclude pregnancy before initiation. Advise effective non-hormonal contraception in women of childbearing potential who are not confirmed postmenopausal.
Driving: May cause fatigue, dizziness, and visual disturbances. Patients should be cautioned about operating machinery or driving until they know how the drug affects them.
| Estrogen-containing therapies (HRT, oral contraceptives) | Antagonizes the therapeutic effect of exemestane. | Major - Contraindicated |
| Strong CYP3A4 inducers (e.g., Rifampicin, Phenytoin, Carbamazepine, St. John's Wort) | May significantly decrease exemestane plasma levels, reducing efficacy. | Major - Avoid or monitor closely; dose increase may be needed. |
| Strong CYP3A4 inhibitors (e.g., Ketoconazole, Itraconazole, Clarithromycin, Ritonavir) | May increase exemestane plasma levels, potentially increasing toxicity. | Moderate - Monitor for increased side effects. |
| Tamoxifen | Co-administration reduces exemestane plasma levels by 45%. Not recommended sequentially without a washout period. | Major - Avoid concomitant use. |
| Warfarin | Potential for increased INR and bleeding risk. Mechanism unclear. | Moderate - Monitor INR closely when starting or stopping exemestane. |
Same composition (Exemestane (25mg)), different brands: