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Letrozole (Femara)

Aromatase Inhibitororal · inferred

Non-steroidal aromatase inhibitor and the most potent of the third-generation AIs, suppressing estradiol by >99% at 2.5 mg/day. Half-life ~48 hours. Steady state in ~2-6 weeks. Often used at lower doses (0.25-0.5 mg) for estrogen management during TRT.

Projected serum levels — 0.50 mg, once daily

Letrozole (Femara)
Letrozole (Femara) modeled serum levels, 0.50 mg once daily over 15 days Population-based pharmacokinetic estimate. Steady state reached after approximately 5 days. 0 0.50 1 1.5 2 Day 0 Day 4 Day 8 Day 11 Day 15 Time on a regular schedule ≈ steady state · day 5
Letrozole (Femara) modeled serum levels with a loading dose of 1.5 mg, then 0.50 mg once daily The first dose is larger so levels approach steady state faster. 0 0.50 1 1.5 2 Day 0 Day 4 Day 8 Day 11 Day 15 Time on a regular schedule

Maintenance schedule: 0.50 mg once daily (oral).

Loading schedule: 1.5 mg on day 1, then 0.50 mg once daily — reaching therapeutic levels sooner.

Modeled steady state after ~5 days: peak ≈ 1.5 mg, trough ≈ 0.98 mg body load. Population-based estimate over 15 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
42 h
Common dose
0.50 mg
Suggested maximum
2.5 mg/day
Reference dose range
1.3–2.5 mg (single dose)
Suggested cadence
once daily
Validated against
2.5 mg oral — Cmax 0.030 mg/L at 1 h

Documented interactions

  • danger
    Carbamazepine (Tegretol) + Letrozole (Femara) CYP induction

    Carbamazepine (Tegretol) inducer of CYP3A4 predicted to change Letrozole (Femara) AUC by ~0.31x

  • danger
    Clarithromycin (Biaxin) + Letrozole (Femara) CYP inhibition

    Clarithromycin (Biaxin) mechanism_based of CYP3A4 predicted to change Letrozole (Femara) AUC by ~2.00x

  • danger
    Diltiazem + Letrozole (Femara) CYP inhibition

    Diltiazem mechanism_based of CYP3A4 predicted to change Letrozole (Femara) AUC by ~2.00x

  • danger
    Efavirenz (Sustiva) + Letrozole (Femara) CYP induction

    Efavirenz (Sustiva) inducer of CYP3A4 predicted to change Letrozole (Femara) AUC by ~0.20x

  • danger
    Esomeprazole (Nexium) + Letrozole (Femara) CYP inhibition

    Letrozole (Femara) reversible_inhibitor of CYP2C19 predicted to change Esomeprazole (Nexium) AUC by ~2.07x

  • danger
    Grapefruit (whole fruit) + Letrozole (Femara) CYP inhibition

    Grapefruit (whole fruit) mechanism_based of CYP3A4 predicted to change Letrozole (Femara) AUC by ~2.00x

Serum checks 86 modeled interaction pairings for letrozole (femara) 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

    Comprehensive pharmacology review showing letrozole achieves >99% aromatase inhibition at 2.5 mg/day with a 2-4 day half-life and steady state in ~60 days.

  2. Effect of Age and Single Versus Multiple Dose Pharmacokinetics of Letrozole (Femara) in Breast Cancer Patients Pfister CU et al. · Biopharmaceutics & Drug Disposition, 2001 DOI

    Found letrozole half-life and AUC increased 42% and 28% respectively at steady state vs single dose, with no clinically significant effect of age on pharmacokinetics.

  3. The Discovery and Mechanism of Action of Letrozole Bhatnagar AS · Breast Cancer Research and Treatment, 2007 DOI

    Detailed review of letrozole mechanism as the most potent third-generation non-steroidal aromatase inhibitor, with binding affinity 10,000x greater than substrate androstenedione.

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