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Anastrozole (Arimidex)

Aromatase Inhibitororal · inferred

Non-steroidal aromatase inhibitor that reduces estradiol by ~80% at 1 mg/day. Half-life ~46 hours supports every-other-day or twice-weekly dosing for estrogen management during testosterone therapy. Steady state reached in ~7 days.

Projected serum levels — 0.50 mg, twice weekly

Anastrozole (Arimidex)
Anastrozole (Arimidex) modeled serum levels, 0.50 mg twice weekly over 18 days Population-based pharmacokinetic estimate. Steady state reached after approximately 7 days. 0 0.25 0.50 0.75 1 Day 0 Day 4 Day 9 Day 13 Day 18 Time on a regular schedule ≈ steady state · day 7
Anastrozole (Arimidex) modeled serum levels with a loading dose of 0.71 mg, then 0.50 mg twice weekly The first dose is larger so levels approach steady state faster. 0 0.25 0.50 0.75 1 Day 0 Day 4 Day 9 Day 13 Day 18 Time on a regular schedule

Maintenance schedule: 0.50 mg twice weekly (oral).

Loading schedule: 0.71 mg on day 1, then 0.50 mg twice weekly — reaching therapeutic levels sooner.

Modeled steady state after ~7 days: peak ≈ 0.58 mg, trough ≈ 0.17 mg body load. Population-based estimate over 18 days for a 0.50 mg dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.

Key facts

Category
Aromatase Inhibitor
Route modeled
Oral
Model confidence
inferred
Half-life
2.1 days
Common dose
0.50 mg
Suggested maximum
1 mg/day
Reference dose range
0.25–1 mg (single dose)
Suggested cadence
twice weekly
Validated against
1 mg oral — Cmax 0.013 mg/L at 2 h

Documented interactions

  • contraindicated
    Clarithromycin (Biaxin) + Anastrozole (Arimidex) CYP inhibition

    Clarithromycin (Biaxin) mechanism_based of CYP3A4 predicted to change Anastrozole (Arimidex) AUC by ~5.14x

  • contraindicated
    Diltiazem + Anastrozole (Arimidex) CYP inhibition

    Diltiazem mechanism_based of CYP3A4 predicted to change Anastrozole (Arimidex) AUC by ~5.14x

  • contraindicated
    Efavirenz (Sustiva) + Anastrozole (Arimidex) CYP induction

    Efavirenz (Sustiva) inducer of CYP3A4 predicted to change Anastrozole (Arimidex) AUC by ~0.14x

  • contraindicated
    Grapefruit (whole fruit) + Anastrozole (Arimidex) CYP inhibition

    Grapefruit (whole fruit) mechanism_based of CYP3A4 predicted to change Anastrozole (Arimidex) AUC by ~5.14x

  • contraindicated
    Grapefruit Juice + Anastrozole (Arimidex) CYP inhibition

    Grapefruit Juice mechanism_based of CYP3A4 predicted to change Anastrozole (Arimidex) AUC by ~5.14x

  • contraindicated
    Paxlovid (Nirmatrelvir/Ritonavir) + Anastrozole (Arimidex) CYP inhibition

    Paxlovid (Nirmatrelvir/Ritonavir) mechanism_based of CYP3A4 predicted to change Anastrozole (Arimidex) AUC by ~5.14x

Serum checks 61 modeled interaction pairings for anastrozole (arimidex) across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.

Research behind this entry

  1. An Overview of the Pharmacology and Pharmacokinetics of the Newer Generation Aromatase Inhibitors Anastrozole, Letrozole, and Exemestane Buzdar AU · Cancer, 2002 DOI

    Comparative pharmacology review showing anastrozole 1 mg daily achieves plasma half-life of 41-48 h, steady-state within 7 days, and greater than 96% aromatase inhibition with high selectivity.

  2. A Phase I Study of the Pharmacokinetics, Pharmacodynamics, and Safety of Single- and Multiple-Dose Anastrozole in Healthy, Premenopausal Female Volunteers Leder BZ et al. · Fertility and Sterility, 2004 DOI

    Phase I trial in 26 premenopausal women demonstrating linear, predictable anastrozole pharmacokinetics with 5-20 mg single doses and multiple daily dosing regimens.

  3. Pharmacokinetics and Pharmacodynamics of Anastrozole in Pubertal Boys with Recent-Onset Gynecomastia Mauras N et al. · Journal of Clinical Endocrinology & Metabolism, 2009 DOI

    Characterized anastrozole PK in pubertal boys showing effective estradiol suppression, with elimination half-life consistent with adult data and supporting once-daily dosing for gynecomastia.

3 published studies referenced in the app, each with a plain-language summary.