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
poster:chemist
thread:347377
URL: http://www.dr-bob.org/babble/20040515/msgs/347574.html