Femara (Letrozole) Pharmacokinetics
Femara has a terminal elimination half-life of approximately 2 days (about 40-48 hours), and plasma concentrations peak within 2 hours after oral administration. 1
Peak Plasma Concentration (Tmax)
- Letrozole reaches peak plasma levels within 2 hours after oral administration 1
- This rapid absorption occurs regardless of food intake, as absorption is not affected by food 1
- The drug is rapidly and completely absorbed from the gastrointestinal tract 1
Half-Life Details
- The terminal elimination half-life is approximately 2 days (ranging from 40-48 hours in various studies) 1, 2
- More specifically, studies report the half-life as 2-4 days depending on the patient population 2
- After a single dose, the terminal half-life is approximately 41-48 hours 2
Time to Steady State
- Steady-state plasma concentrations are reached in 2 to 6 weeks with daily 2.5 mg dosing 1
- Some studies report steady state is achieved after approximately 60 days of continuous daily dosing 2
- At steady state, plasma concentrations are 1.5 to 2 times higher than predicted from single-dose measurements, indicating slight non-linearity in pharmacokinetics 1
Important Clinical Considerations
- The long half-life means maximal estrogen suppression is achieved within 2-3 days of treatment initiation and is maintained throughout treatment 1, 3
- Despite the 2-day half-life, continuous accumulation does not occur once steady state is reached 1
- Age does not significantly affect letrozole pharmacokinetics in adults ranging from 35 to over 80 years 1
- Approximately 90% of letrozole is weakly protein-bound with a large volume of distribution (approximately 1.9 L/kg) 1