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Dr. Bob is Robert Hsiung, MD,
bob@dr-bob.orgShown: posts 1 to 4 of 4. This is the beginning of the thread.
Posted by sisyphus on October 3, 2003, at 23:08:40
Dear all,
Can anyone explain in detail what exactly half-life is?
To cite Wellbutrin as an example. It's half-life is 20hrs. Does it mean that when a person takes a dose of 150mg Wellbutrin, 87% of the medication will leave the body of the person when he/she goes to toilet to pee 20hrs later?
Thanks.
Posted by krybrahaha on October 4, 2003, at 0:57:51
In reply to Half-life, posted by sisyphus on October 3, 2003, at 23:08:40
Half Life is the amount of time it takes for just half the drug to leave your system. You say that Wellbutrin has a 20 hr half life, it will take 10 hrs just for half of whatever dose your on to leave your system.
Anyone correct me if Im wrong -
Posted by omegon on October 4, 2003, at 6:01:48
In reply to Re: Half-life, posted by krybrahaha on October 4, 2003, at 0:57:51
No, 20 hours for _half_ the dose to leave your system. Then a further 20 hours for half the remainder, leaving you with a quarter of the original dose; and so on. Obviously it's a gradual, smooth curve, and it decreases more slowly as the level remaining gets lower. It results from continuous breakdown and excretion of the drug - it doesn't drop in steps every 20 hours!
What this means is that drugs with a short half-life need to be taken more frequently, or in slow-release formulations, in order to get a reasonably smooth, continuous effect; you want to avoid a dramatic drop in levels by the time you take the next dose. An exception to this might be if you actually want the levels to be lower at some time of day; for example, if it causes insomnia, it might be helpful to take it in the morning and let the level fall a bit by bedtime.
Since a drug with a short half-life will leave your system completely only a few days after you stop taking it, it may be more likely to cause withdrawal problems if you stop abruptly.
> Half Life is the amount of time it takes for just half the drug to leave your system. You say that Wellbutrin has a 20 hr half life, it will take 10 hrs just for half of whatever dose your on to leave your system.
Posted by Sebastian on October 4, 2003, at 18:20:59
In reply to Half-life, posted by sisyphus on October 3, 2003, at 23:08:40
I don't think it makes a difference if you pee or not. Just that it breakes down in your system.
Your hilarious!
This is the end of the thread.
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