hey everybody today we are doing some fun facts on pharmacokinetic properties of medications for today's reinhardt's rundown and we're focusing for this video on the elimination half-life of a drug first things first a definition what exactly is an elimination half-life a drug's half-life or the t-one half is the time it takes for the concentration of a drug in the plasma or in the bloodstream to reduce to half the original value so let's look at an example with ambien or zolpidem zolpidem is a hypnotic used for sleep in patients suffering with insomnia the half-life is about two and a half to three hours so for our example we'll use the three hours if my patient takes a dose of zolpidem 10 milligrams at 9 pm in the evening 3 hours later at midnight 50 of the dose has been eliminated 50 remains in the blood so 5 milligrams will remain in the bloodstream three more hours later it's three a.m dose is cut by another fifty percent 2.5 milligrams in the blood three more hours 1.25 milligrams remain in the bloodstream three hours later again 0.625 milligrams in the bloodstream three hours later it's now noon the next day 97 of the drug is eliminated from the blood and only a very small amount remains in the bloodstream overall it takes about five half-lives for 97 percent of the drug to be eliminated and seven half-lives for 99 of a drug to be eliminated from the blood now depending on the drug this doesn't 100 percent mean it's not detectable on a blood test or that it won't be picked up on a drug screen but it does help us understand when the drug is therapeutically considered to be eliminated from the blood thanks for watching in our next video we'll look at how a medications half-life helps us determine dosing frequency and go through a real-life example with an ace inhibitor one of the most common medications we see for blood pressure and heart failure that's the reinhardt's rundown