Good question.

Letro's half-life is about 6 hrs, this means its terminal half-life (last one, or 8th incidence) is experienced at around 48 hrs. Now generally speaking, and note I said "generally" you are supposed to Septuple (seven-fold) the terminal half-life to account for ALL residual metabolite degradation, i.e. upper limit detection times. This gives us 336 hrs or about 14 days.



However, because Letro is pharmacologically odd in that concentrations are somewhat non-linear, i.e. continuous accumulation doesn't occur past a specific point (at least in doses up to 2.5mgs ED), I'd say it would degrade even more rapidly.

http://www.pharma.us.novartis.com/pr...pdf/Femara.pdf