The presenters use the example of Klonopin (clonazepam), a medication for anxiety. That lengthy stretch is the same amount of time it will take for the drug to be eliminated from the system.
The half-life is the amount of time necessary for the concentration of the drug in the bloodstream of the body to be reduced by one-half. The time it will take for a drug to reach a steady state, or full effectiveness, in the system is based on that half-life.Īnd sometimes it just isn't all that fast.Ī presentation from the University of Florida entitled ' Basic Biopharmaceutics' clarifies that, 'It takes one half-life to reach 50%, 2 half-lives to reach 75%, 3 half-lives to reach 87.5%, 3.3 half-lives to reach 90%, 4 half-lives to reach 93.75% of steady state. In most clinical situations, the attainment of steady state can be assumed after 3-5 half-lives.'Īs you can see, two halves do not make a whole.
Anyone who has ever popped a cholesterol-lowering drug, or an antidepressant, or an anti-seizure medication, and expected to wake up the next day with a changed life knows that taking medicine is often a waiting game.Īnd anyone who has experienced an adverse side effect from a drug, and is waiting anxiously for it to clear the system, knows the same.īoth the time it will take for a drug to be effective, and the time it will take for it to leave the body completely, depend on a drug's half-life.
