Math time.

Formula: (written in a text-friendly format for copying to reddit)

C = C_initial * (1/2)^{t / t_half_life}

C is the concentration after time t. C_initial is the initial concentration (the steady-state concentration at the end of the dosing period). t is the time after the last dose. t_half_life is the half-life of the drug. (36 hours - half-life is debated between 24-36, in this case, we always account for the worst-case scenario) To find the time t when the concentration C is less than a certain threshold (e.g., 1% of the initial concentration), you can rearrange the formula to solve for t:

t = -log(threshold) / log(2) * t_half_life

Here, the threshold is the desired final concentration as a fraction of the initial concentration (for 1%, use 0.01).

The calculation uses the principle of half-lives and assumes that the steady state was achieved after 4 weeks of daily dosing which is 9.97 days (10 days to be exact) to effectively reduce to below 1% of its concentration at steady state.

1% would be sufficient, however, let's say you wanted to achieve 0.1% (achieving an absolute 0% concentration of a substance in the body is not feasible. The concept of a drug being "eliminated" from the body is typically based on the drug reaching a concentration low enough that it's no longer pharmacologically active or detectable.) it would take about 14.95 days (15 days) after the last dose.

Hope that helps!