Aromasin (Exemestane)
Exemestane · Exe · Suicidal AI
Steroidal (suicidal) aromatase inhibitor; permanently inactivates aromatase enzyme.
Key takeaways
- Irreversible ("suicidal") aromatase inhibitor; estradiol recovery requires new enzyme synthesis over days.
- Roughly 23-hour half-life with very low (~5%) oral bioavailability; food changes exposure.
- Oncology label is 25 mg daily with food; off-label use runs far lower, bloodwork-guided.
- Overshoots resolve slowly because inactivation is irreversible; conservative dosing matters.
Overview
What it is
Aromasin (exemestane) is a steroidal, irreversible aromatase inhibitor approved for estrogen-receptor-positive breast cancer and used off-label to manage estradiol during testosterone therapy or anabolic cycles. As a mechanism-based ("suicidal") inactivator it permanently disables the aromatase enzyme, so estradiol recovery requires new enzyme synthesis over several days.
Pharmacokinetics
The half-life is roughly 23 hours, but oral bioavailability is very low (the dataset uses 5%) and food changes exposure, so real-world suppression tracks repeated dosing more than single-dose levels.
What the evidence says
The IES trial showed switching to exemestane after 2–3 years of tamoxifen improved breast cancer outcomes, so the oncology evidence is solid. Off-label use lacks trials and shares the class risk of over-suppression: joint pain, libido loss, lipid deterioration, and mood disturbance when estradiol runs too low. Because inactivation is irreversible, overshoots resolve only as new enzyme is made.
Reported dosing protocols
Protocols reported in research literature and clinic/community use — informational context, not a dosing recommendation.
| Use case | Dose | Route | Frequency | Duration |
|---|---|---|---|---|
| Breast cancer (label) | 25 mg after a meal | Oral | Once daily | 2–3 years to complete 5 years of endocrine therapy (adjuvant) |
| Estradiol control on-cycle (community) | 6.25–12.5 mg | Oral | 1–2× weekly | On-cycle, as needed |
Pharmacokinetic summary
- Model tier
- Advanced (t½ + Cmax + Tmax + F)
- Half-life
- 22.7 hours
- Cmax
- 57.6 ng/mL
- Tmax
- 0.1 days
- Bioavailability
- 5%
- Typical dose
- 6.25–25 mg
Frequently asked questions
What does "suicidal" aromatase inhibitor mean?
Exemestane is processed by the aromatase enzyme into a form that permanently disables it. Estradiol can't recover until the body synthesizes new enzyme, which takes days, so suppression outlasts the drug's 23-hour half-life.
Why does the label say to take exemestane with food?
A high-fat meal raises exemestane absorption substantially; the PK model in the dataset explicitly incorporates the food effect. The label recommends dosing after a meal to keep exposure consistent.
Aromasin vs arimidex — which is harsher?
Exemestane's irreversible action makes over-suppression slower to correct, while anastrozole rebounds faster. Some lipid data favor exemestane slightly. Off-label, both are dosed far below oncology levels and driven by estradiol bloodwork.
References
- PMC exemestane PK
- Coombes et al., NEJM 2004 — Intergroup Exemestane Study — Switching to exemestane after 2–3 years of tamoxifen improved disease-free survival.
- Exemestane PK/PD model, Br J Clin Pharmacol 2005 — Model incorporating the food effect used for the plotter profile.
Related articles
Related compounds
Comments
Loading comments…