Best Time to Take Anastrozole
Anastrozole can be taken at any time of day, with or without food, as timing does not affect its efficacy or safety. The key is to take it consistently at the same time each day to maintain steady drug levels and optimize adherence.
Dosing Flexibility
The FDA-approved prescribing information explicitly states that anastrozole 1 mg once daily "can be taken with or without food" 1. This provides maximum flexibility for patients to integrate the medication into their daily routine in whatever manner best supports adherence.
Pharmacokinetic Rationale
The pharmacokinetic profile of anastrozole supports flexible timing:
Food does not meaningfully affect absorption: While food reduces the rate of absorption (decreasing Cmax by 16% and delaying Tmax from 2 to 5 hours), it does not affect the overall extent of absorption 1. This means total drug exposure remains unchanged regardless of whether the medication is taken with meals or on an empty stomach.
Long half-life allows once-daily dosing: With a mean elimination half-life of 50 hours, anastrozole maintains stable plasma concentrations with once-daily administration 1. Steady-state levels are reached after approximately 7 days of daily dosing and are 3-4 fold higher than single-dose levels 1.
Sustained estrogen suppression: The drug provides approximately 70% estradiol suppression within 24 hours and 80% suppression after 14 days, with suppression maintained for up to 6 days after cessation 1. This robust and sustained pharmacodynamic effect is independent of the specific time of administration.
Practical Recommendations
Choose a consistent time that maximizes adherence:
Morning dosing: May be preferred by patients who take other morning medications or who want to establish a routine linked to breakfast or morning activities
Evening dosing: May be suitable for patients who experience side effects like joint stiffness or hot flashes, as taking the medication at bedtime might make these symptoms less noticeable during sleep
With or without food: Either approach is acceptable; patients experiencing mild gastrointestinal upset (reported in 29-33% of patients) 2 may prefer taking it with food, though this is not required
Common Pitfall to Avoid
The most important factor is consistency and adherence, not the specific time chosen. In the IBIS-II trial, 5-year adherence was only 68% in the anastrozole group 3, and women reporting gynecologic symptoms at 6 months were significantly less likely to be adherent at 4.5 years 3. Focus counseling on maintaining daily adherence rather than worrying about optimal timing, as the drug's long half-life and sustained pharmacodynamic effects make it forgiving of minor variations in administration time.