What stops meds from over-accumulating?

Question

So I took a look at a popular blood pressure medication, Lisinopril, and found that it has a 12.6 hour half-life (meaning it reaches half dosage, in the body, every 12.6 hours).
(For this I'm rounding down to 12 hours for simplicity sake.)
(This medication is *usually* taken once, every 24 hours.)

So then I did some math:

Day 1:
0 hr -- 20 mg
12 hr -- 10 mg
24 hr -- 5 mg + 20 mg = 25 mg

Day 2:
36 hr -- 2.5 mg + 10 mg = 12.5 mg
48 hr -- 1.25 mg + 5 mg + 20 mg = 26.25 mg

Day 3:
60 hr -- .625 mg + 2.5 mg + 10 mg = 13.125 mg
72 hr -- .3125 mg + 1.25 mg + 5 mg + 20 mg = 26.5625 mg

Day 4:
84 hr -- .15625 mg + .625 mg + 2.5 mg + 10 mg = 13.28125 mg
96 hr -- .078125 mg + .3125 mg + 1.25 mg + 5 mg + 20 mg = 26.640625 mg

Day 5:
108 hr -- .0390625 mg + .15625 mg + .625 mg + 2.5 mg + 10 mg = 13.3203125 mg
120 hr -- 0.01953125 mg + .078125 mg + .3125 mg + 1.25 mg + 5 mg + 20 mg = 26.66015625 mg


(Or in short...)
Day 1: 25 mg
Day 2: 26.25 mg
Day 3: 26.5625 mg
Day 4: 26.640625 mg
Day 5: 26.66015625 mg

So as you can see, the accumulation rate is
-> 1.25 mg
-> .3125 mg
-> .078125 mg
-> 0.01953125 mg


Now, I know as well as the next person that at a low enough dosage the amount becomes negligible and the kidneys remove the remainder entirely from the body... but I do not know the minimum dosage which that happens at.
(I am also aware that the half-life rate is different for each person due to metabolic and absorption rate differences: everybody's body is different.)

So I'm left asking this:
At what point does the medication (or any medication) stop accumulating in the body as to prevent toxicity or overdose?

Answer 1

It's formulated in a way at which you hit a limit. As you can see, it appears that particular medicine in the quantity being taken essentially has a limit of slightly below 27 (remember precalc and calc!). It will never hit 27mg because the amount that keeps increasing each day gets smaller and smaller.



It's pharmacological math. And it's why many medications never get approved--their effective dose (dose needed to work) is way too close to an overdose. If, for instance, lisinopril was toxic at 30mg, it would never have been approved because if someone took a pill a few hours early they would hit that 30mg for a bit.

Answer 2

Graviola gets rid of minerals that stay in your body and most of the drugs that become toxic.

Answer 3

Blah, blah, blah... it will only stop when you stop taking the blasted toxic chemicals. It takes a very long time for the body to get rid of these toxins, and some may just stay there for ever.