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Dr. Bob is Robert Hsiung, MD,
bob@dr-bob.orgShown: posts 1 to 19 of 19. This is the beginning of the thread.
Posted by babs on February 5, 2003, at 2:24:43
if geodon has a half-life of 7 hours, how long will it take to get out of my system? i was on it for ten days. thanks, babs
Posted by AffectsHer on February 5, 2003, at 10:14:16
In reply to what does half-life mean?, posted by babs on February 5, 2003, at 2:24:43
Hey Babs, a half life is the term used when the drug has reached peak effectiveness and then starts to leave your system... Half lives are usually very important when going off any drugs for any reason, surgery,, switching to a new drug etc... Sometimes it's also good to know the half life to determine peak effect if you're having nasty side effects (eg. if having insomnia problems, take the drug earlier in the day so it will have a chance to get a bit more out of your system before sleep time.)
Does that help?
In terms of your latter question (original?) that's hard to say as the drug needs to flush out at a certain rate, specific to the drug...my math is quite poor and I'm not familiar with what you are on so a doctor or maybe another site might be able to help you.
Cheers,
K.
Posted by ShelliR on February 5, 2003, at 10:47:28
In reply to what does half-life mean?, posted by babs on February 5, 2003, at 2:24:43
Babs,
The half-life of a drug is the time is takes for 50% of the drug to be no longer in your system.
Shelli
Posted by sl on February 5, 2003, at 11:11:03
In reply to what does half-life mean?, posted by babs on February 5, 2003, at 2:24:43
To follow up on what the previous poster said, if the halflife is 7 hours, you should be safe to try something else within 24-48 hours. If the potential interaction between the old and the new is lethal, go with a longer period of time (I'm not a doc and I wouldn't want you to get sick or die cuz you gambled on my info being right), and/or call a doc or pharmacist and ask them if they think it'll be okay. If the potential interaction is just "synergistic sedation" I'd say just take it and expect to spend the first day or two laying around the house watching TV and napping (so if you have a life, plan to start on a Friday evening when you don't have to be anywhere til Monday, and if it doesn't have that effect cuz the Geodon is mostly gone, well then you're better off than you expected!).
I wish you well in your next try! :)
sl
Posted by babs on February 5, 2003, at 11:16:23
In reply to Re: what does half-life mean?, posted by sl on February 5, 2003, at 11:11:03
Thanks SL- the geodon made me really sick (flu) and I want to know when I will stop feeling sick. It' been about 36 hours since I took my last dose and I still feel awful!
Posted by ricardo on February 5, 2003, at 12:00:40
In reply to Re: what does half-life mean? » sl, posted by babs on February 5, 2003, at 11:16:23
I know that the idea of half-life is directly connected with withdrawal side-effects. I'd really love it if someone could explain that to me...
Incidentally, my new p-doc has put me on Tofranil (imipramine). Does anybody know anything about it. I know it's an old tricyclic...
Cheers,
Ric
Posted by babs on February 5, 2003, at 12:47:31
In reply to Re: what does half-life mean?, posted by ricardo on February 5, 2003, at 12:00:40
Hi Ric- I was on imipramine for eleven yaers with great success- it's a very calming drug. The worst side effects were dry mouth (I just drank a lot of water and chewed sugarfree gum)and constipation (just pay attention to diet and exercise- it got better with time). No sexual side effects like some of the newer drugs. I miss it actually and if it wouold work again, I'd go back on it in a heartbeat!
Posted by ShelliR on February 5, 2003, at 13:07:25
In reply to Re: what does half-life mean?, posted by sl on February 5, 2003, at 11:11:03
<To follow up on what the previous poster said, if the halflife is 7 hours, you should be safe to try something else within 24-48 hours.>
sl,
how did you calculate the 24-48 hour period in relation to a half-life of 7 hours?
tia,
Shelli
Posted by jumpy on February 5, 2003, at 18:03:35
In reply to what does half-life mean?, posted by babs on February 5, 2003, at 2:24:43
> if geodon has a half-life of 7 hours, how long will it take to get out of my system? i was on it for ten days. thanks, babs
Half life is the amount of time it take the body to remove "half" of a substance from the blood stream. In general, multiply the half life times "5" to determine how long it take a drug to clear your system or how long it takes a drug to reach a steady state in the blood stream. So, if the half life is 7 hours .... after about 7*5=35 ... 35 hours the drug will be cleared from the system.
Jumpy
PS Thing get complicated if the drug has an active metabolite with a diferent half life then the parent drug or if the drug is easily stored in fat tissue.
Posted by OddipusRex on February 6, 2003, at 11:19:48
In reply to Re: what does half-life mean? » babs, posted by jumpy on February 5, 2003, at 18:03:35
So is the half life of what's left also 7 hours etc. so after 5 half lifes (35 hours) there will be 1/32 of the original concentration? (I liked to read during math class myself)
> > if geodon has a half-life of 7 hours, how long will it take to get out of my system? i was on it for ten days. thanks, babs
>
> Half life is the amount of time it take the body to remove "half" of a substance from the blood stream. In general, multiply the half life times "5" to determine how long it take a drug to clear your system or how long it takes a drug to reach a steady state in the blood stream. So, if the half life is 7 hours .... after about 7*5=35 ... 35 hours the drug will be cleared from the system.
>
> Jumpy
>
> PS Thing get complicated if the drug has an active metabolite with a diferent half life then the parent drug or if the drug is easily stored in fat tissue.
>
Posted by Larry Hoover on February 7, 2003, at 10:56:59
In reply to Back to half-life......... » sl, posted by ShelliR on February 5, 2003, at 13:07:25
> <To follow up on what the previous poster said, if the halflife is 7 hours, you should be safe to try something else within 24-48 hours.>
>
> sl,
>
> how did you calculate the 24-48 hour period in relation to a half-life of 7 hours?
>
> tia,
>
> ShelliThe relationship between half-life (t1/2)and concentration is n(t1/2) = (1/2)^n * initial concentration. So, for a period of four half-lives, the remaining concentration is (1/2)^4, or 1/16. In this example, the half-life is seven hours, so at 28 hours, the concentration is 1/16 of the peak concentration. What should be noted, however, is that the half-life timing period begins not at the time of ingestion, but at the time of peak plasma concentration, which might be as much as hours after ingestion.
At six half lives, the concentration would be 1/64, probably a negligible amount. As Geodon does not have active metabolites, and assuming two hours to reach maximal plasma concentration, at 44 hours ( 6 * 7 + 2)post ingestion there would be 1/64 of the peak level remaining in the blood.
Lar
Posted by Larry Hoover on February 7, 2003, at 15:41:23
In reply to Re: Back to half-life........., posted by Larry Hoover on February 7, 2003, at 10:56:59
> > <To follow up on what the previous poster said, if the halflife is 7 hours, you should be safe to try something else within 24-48 hours.>
> >
> > sl,
> >
> > how did you calculate the 24-48 hour period in relation to a half-life of 7 hours?
> >
> > tia,
> >
> > Shelli
>
> The relationship between half-life (t1/2)and concentration is n(t1/2) = (1/2)^n * initial concentration.That shouldn't be an equal sign, but instead is an arrow. I.e. concentration at elapsed time t = (1/2)^(t/(t1/2)) * initial concentration.
Posted by Larry Hoover on February 7, 2003, at 15:51:34
In reply to Re: Back to half-life...(correction), posted by Larry Hoover on February 7, 2003, at 15:41:23
Posted by viridis on February 8, 2003, at 0:04:19
In reply to Re: that doesn't look right either (arghh!) (nm), posted by Larry Hoover on February 7, 2003, at 15:51:34
Half-life is a somewhat confusing concept (I know, because I regularly have to explain half-lives of radioisotopes to students in terms of carbon dating of fossils etc.).
The basic idea (I'll leave out the math) is that one half-life for a med is the time it takes half the original amount of the drug to clear your system. So, many people would say that, if the half-life is 10 hours, then all of it should be gone in 20 hours. But it doesn't work that way -- instead, in the next 10 hours, half of what's remaining will be gone, then half of that in the next 10 hours etc. Thus, 50% is gone after 10 hours, 75% after 20 hours, 87.5% after 30 hours, and so on.
So, theoretically, it's never completely gone (although really it will be eventually, for all intents and purposes).
I can't address the specifics of certain meds, but in general, after several half-lives, there's a negligible amount left. Just as a reference point, for the radioisotopes of phosphorus that I work with (which are fairly potent but have short half-lives), they're considered safe to throw in the regular trash after 10 half-lives. This is an extremely conservative, safety-based approach, and at that point there's no more radioactive isotope left than what's found naturally in the environment.
Posted by bluedog on February 8, 2003, at 12:58:00
In reply to Re: Half-life, posted by viridis on February 8, 2003, at 0:04:19
Here's an interesting question for you regarding the half life of diazepam. I have been driving myself crazy trying to do the maths on this one but I have been assuming a completely linear decrease in the amount of diazepam that will show up in my blood plasma levels at certain intervals. In the Benzo equivalence charts it shows that diazepam (and it's metabolite) have a a half life of 30-200 hours. Now for the sake of simplicity I have actually assumed that the half life for a healthy average male of say around about 30 years of age would probably be closer to 24 hours.
I take the following doses of diazepam on a daily basis:
8.00am - 5mg
2.00pm - 5mg
10.00pm - 5mg.I set my alarm for 7.00am each morning and am interested to know what my blood plasma level of diazepam will be each day when my alarm sounds. My VERY crude calculations (assuming a half life of only 24 hours and a completely linear decrease in the blood plasma level of the drug) have yielded the following results.
DAY ONE - Prior to to commencing taking the drug when my alarm sounds at 7.00am my level of diazepam will of course be nil.
DAY TWO - at 7.00am my blood level will be approximately 10.63mg
DAY THREE - at 7.00am my blood level will be approximately 16.89 mg
I am confused and believe that at this rate of consumption the my blood plasma level of diazepam (or it's metabolite) will continue to accumulate and will actually increase on a daily basis. My questions are as follows:-
1) Are my calculations and assumptions correct?
2) Is it not the case that with each successive day the level of diazepam in my blood will continue to increase leading to a higher and higher level of the drug in my system with the consequence that I will find it increasingly difficult to get out of bed each morning when my alarm sounds at 7.00am?
3) Would the levels continue to increase so that I would eventually become none functional and could the levels in theory continue to increase until I would end up with a fatal accumulation of the drug in my system? Of course if the half life is in fact closer to the 30-200 hours shown in the benzo equivalence charts then the accumulation in my system may be even more pronounced
4) Can you please explain this to me and clarify whether my assumptions are correct or whether in fact the blood plasma levels of diazepam in my system would actually at some point stabilise and if so at what level (in mg) would this stabilisation occur?
My gut feeling says that my assumptions must be wrong but I simply don't know why. I hope my questions will not drive you around the twist like they have done to me. Then again you may enjoy my questions and be able to explain it all to me :):).
Thanks in advance guys
warm regards
bluedog
Posted by Larry Hoover on February 8, 2003, at 13:23:14
In reply to Re: Half-life - Larry Hoover and » viridis, posted by bluedog on February 8, 2003, at 12:58:00
> Here's an interesting question for you regarding the half life of diazepam. I have been driving myself crazy trying to do the maths on this one but I have been assuming a completely linear decrease in the amount of diazepam that will show up in my blood plasma levels at certain intervals.
It's not linear, it's logarithmic. The converse statement would be that as serum concentration increases, excretion increases exponentially.
(snip)
> I am confused and believe that at this rate of consumption the my blood plasma level of diazepam (or it's metabolite) will continue to accumulate and will actually increase on a daily basis.Early on, there will be a relatively large fluctuation in serum levels because the dosing is intermittent enough that excretion is quite variable. As the serum concentration increases, however, excretion rates increase exponentially, until such time as net excretion between doses equals intake dosing. At that point, you have reached what is called steady-state or equilibrium pharmacokinetics.
>My questions are as follows:-
>
> 1) Are my calculations and assumptions correct?Simply put, no.
> 2) Is it not the case that with each successive day the level of diazepam in my blood will continue to increase leading to a higher and higher level of the drug in my system with the consequence that I will find it increasingly difficult to get out of bed each morning when my alarm sounds at 7.00am?If anything, you will find your body accomodates the medication as you become accustomed to the steady-state serum concentration.
> 3) Would the levels continue to increase so that I would eventually become none functional and could the levels in theory continue to increase until I would end up with a fatal accumulation of the drug in my system? Of course if the half life is in fact closer to the 30-200 hours shown in the benzo equivalence charts then the accumulation in my system may be even more pronounced.The only effect of half-life here is how long it takes for your body to reach equilibrium conditions, which is also affected, of course, by how often and how much you take. In any case, I would expect you to reach equilibrium in no more than three days time.
>
> 4) Can you please explain this to me and clarify whether my assumptions are correct or whether in fact the blood plasma levels of diazepam in my system would actually at some point stabilise and if so at what level (in mg) would this stabilisation occur?That level would be determined by your individual excretion capacity. Given the roughly ten-fold difference in half-life measured in clinical practice, you can see that determining the equilibrium concentration for you *specifically* could only be determined by blood draw and analysis.
> My gut feeling says that my assumptions must be wrong but I simply don't know why. I hope my questions will not drive you around the twist like they have done to me. Then again you may enjoy my questions and be able to explain it all to me :):).
>
> Thanks in advance guys
> warm regards
> bluedogWell, let's hope my answers have helped. ;-)
Lar
Posted by babs on February 8, 2003, at 14:41:05
In reply to Re: Half-life - Larry Hoover and, posted by Larry Hoover on February 8, 2003, at 13:23:14
Thanks for all you replies. According to my calculations (Geodon has a half life of 7 hours and I stopped taking it 120 hours ago) this stuff should be out of my system by now. Why do I still feel bad?
Posted by bluedog on February 10, 2003, at 4:53:17
In reply to Re: Half-life - Larry Hoover and, posted by Larry Hoover on February 8, 2003, at 13:23:14
Pharmacology is not my strongest point.
The human body is an amazingly adaptive organism!!!
regards
bluedog
Posted by Larry Hoover on February 10, 2003, at 10:24:47
In reply to Thanks Larry » Larry Hoover, posted by bluedog on February 10, 2003, at 4:53:17
> Pharmacology is not my strongest point.
>
> The human body is an amazingly adaptive organism!!!
>
> regards
> bluedogYou're welcome, BD. Just so you can put this into context, other substances do not follow this half-life concept. For example, ethanol is considered to be a zeroth-order drug. It's eliminated at a constant rate, without regard to the initial concentration. If intake exceeds breakdown, you get drunker. If the converse, you get more sober. Acetylsalicylic acid (aspirin) is another zeroth-order drug. That's why the only "cure" for alcohol or aspirin overdose is time (or dialysis).
Most pharmaceuticals are first-order, obeying the logarithmic half-life rule. Yet other drugs are second-order, with yet another type of half-life decay, which *is* concentration dependent. For these, the half-life increases as the concentration decreases. In other words, it takes less time for the concentration to fall by the first half than it does for the concentration to fall by the next quarter (2nd half-life).
Please don't be surprised that this is all a very confusing subject.
Lar
This is the end of the thread.
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