1. Can someone please explain how to find a half life of a drug?
    I had a question in my workbook and I still did not get a straight answer from my instructor. Could someone please explain how they got 25% as the answer?
    ##The literature states that the half-life of a particular drug is 8 hours. This means that _____% of the drug will have been excreted in this time period.
  2. 2 Comments

  3. by   tommycher
    Some drug books will tell you the half life of a drug. Don't know if this helps or not, but the half-life is the time required to reduce by one half the amount of unchanged drug that is in the body at the time equilibrium is established. Then, the drug excretes by half the amount, divided in half each time per each time frame of half life. For instance, say 1000mg has a half life of 4 hours, then in the next 4 hours 250mg will be retained, then in the next 4 hours 125mg will be retained, then in the next 4 hours 62.5mg will be retained, and so on and so forth. Good luck, someday it will make sense.
    Last edit by tommycher on Jan 18, '05
  4. by   11:11
    T 1/2

    Half life can be found by looking it up under pharmacokenitics.

    As I understand it:

    Half life is the period of time required for med concentration to be reduced by half (in plasma).

    Steady state is the concentration of med in the plasma that is therapeutic.

    Time to steady state is usually about five times the half life.

    Steady state can be reached more quickly via loading dose-