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Dr. Bob is Robert Hsiung, MD,
bob@dr-bob.orgShown: posts 1 to 7 of 7. This is the beginning of the thread.
Posted by becksA on May 16, 2004, at 9:19:18
I love what it does for me, but it seems to me that if it is like any other typical long acting drug, while I take it in the morning for work, it should wear off by around dinner time. Is this indeed the case? Looking for a black and white answer here!
Posted by theo on May 16, 2004, at 9:43:09
In reply to Xanax XR - Still haven't gotten the answer... :(, posted by becksA on May 16, 2004, at 9:19:18
Maybe I'm not fully understanding your question because I thought I was pretty clear.
The half life for Xanax XR is around 12 hours, so if you take it at 7:00am, you will start to lose the effects around 7:00pm, aka dinnertime.
This is why my doc has me take it twice daily. If I took one 2mg tablet daily, I felt tired and by evening had anxiety, when I took 1mg tablets twice daily (every 12 hours) I wasn't constantly hitting peaks and valleys because 1mg dosing didn't make my tired, plus I had a constant level of it because I took it every 12 hours (twice daily) because if you use common sense, something with a half life of only 12 hours should be dosed twice daily. Even if the makers of Xanax try to market XR as once daily dosing, it's not realistic because the half life is only 12 hours!!!
Posted by chemist on May 16, 2004, at 11:45:23
In reply to Xanax XR - Still haven't gotten the answer... :(, posted by becksA on May 16, 2004, at 9:19:18
> I love what it does for me, but it seems to me that if it is like any other typical long acting drug, while I take it in the morning for work, it should wear off by around dinner time. Is this indeed the case? Looking for a black and white answer here!
YES. all the best, chemist
Posted by becksA on May 16, 2004, at 18:04:59
In reply to Re: Xanax XR - Still haven't gotten the answer... :( » becksA, posted by chemist on May 16, 2004, at 11:45:23
haha....thanks guys, i appreciate it....i guess i wasn't relaly posing my question too clearly. The fact that I'm going down to 1mg twice daily should mean that I'm only going to have half the amount in me at all times, i.e. it will be working only half as much 24/7...
Posted by chemist on May 16, 2004, at 20:39:18
In reply to Re: Xanax XR - Still haven't gotten the answer... :(, posted by becksA on May 16, 2004, at 18:04:59
> haha....thanks guys, i appreciate it....i guess i wasn't relaly posing my question too clearly. The fact that I'm going down to 1mg twice daily should mean that I'm only going to have half the amount in me at all times, i.e. it will be working only half as much 24/7...
hiya. the answer is that if you take 1 mg at 6 a.m., then - if the bioavailabilty half-life is 12 hours and the elimination follows first-order kinetics - that you will have 0.5 mg of xanax in your system at 6 p.m. you then take a second dose, spiking it to 1.5 mg. now, the first 1 mg dose is going to exponentially decline between the hours of 6 p.m. and tomorrow at 6 a.m., but that dose does not reach zero at 6 a.m. the next day, it's now 0.25 mg xanax, and from your second dosing at 6 p.m. the night before, you have 0.5 mg. so i day after you start at 6 a.m., you have 0.75 mg xanax bioavailable. you take 1 mg, spiking it to 1.75 mg. 12 hours later, there is 0.125 mg + 0.25 mg + 0.5 mg = 0.875 mg xanax bioavailable at 6 p.m. on day 2. however, the 0.125 mg might indeed be lower, but in any case, you will have a spike when you take it (here, i have assumed instant t_{max} AUC on dosing). so you get successive half-lives superposed on each other until you reach a steady-state concentration. hope this helps, and all the best, chemist
Posted by becksA on May 17, 2004, at 4:25:46
In reply to Re: Xanax XR - Still haven't gotten the answer... :( » becksA, posted by chemist on May 16, 2004, at 20:39:18
thank you much.
Posted by chemist on May 17, 2004, at 23:43:33
In reply to Re: Xanax XR - Still haven't gotten the answer... :(, posted by becksA on May 17, 2004, at 4:25:46
> thank you much.
becksA, i sense some resignation on this topic. are you truly satified with the information you have gleaned from the posts in response to your thread? all the best, chemist
This is the end of the thread.
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