1/2 life of arimidex is 7 days - but the real question is how long is it detectable in urine tests...
Anastrozole is eliminated slowly with a plasma elimination half-life of approximately 50 hours in postmenopausal women. The pharmacokinetics of anastrozole are linear over the dose range of 1 to 20 mg and do not change with repeated dosing. Consistent with the 50 hour plasma elimination half-life, plasma concentrations of anastrozole approach steady-state concentrations after 7 days of once daily dosing and are approximately 3- to 4-fold higher than the concentrations observed after a single dose of anastrozole. The protein binding of anastrozole to plasma proteins is about 40% and independent of concentration over a range which includes therapeutic concentrations.