Posted by chemist on May 6, 2004, at 1:57:03
In reply to Re: Question for Chemist about Klonopin » chemist, posted by chess on May 5, 2004, at 23:20:27
hello there....duration of action and half-life of elimination are indeed two different aniamls...but the drug we are talking about is highly plasma-bound...half-life is the time at which half of the initial concentration is detectable in your serum. this is a first-order kinetics problem, as klonopin pharmacodynamics are linear with dose. the real issue is bioavailability, and this is what you are talking about, and is extracted from the AUC (area under the plasma-bound concentration of parent compound vs. time curve). t_1/2} is ln(2)/k, where k is the elimination rate constant (in units of s^{-1}). the AUC is the best measure, not half-life of elimination, as this is as close to getting an independent variable as possible. the rate constant for elimination is a dependent variable (factors include your metabolism, hepatic impairment, other drugs that may enhance/decrease metabolism, GI stuff, etc.). so: how do you correlate AUC with half-life of elimination? with klonopin, because it is highly plasma-bound, the derivative of the function that defines the AUC (i.e., maximum bioavailability) is very close to the elimination half-life. the 1-4 hour estimate by roche is for the peak in AUC. the elimination half-life is sufficiently long enough - and the plasma-binding is high - to ensure that your dose of 1mg at 6 a.m. will be therapeutically active (assuming that 0.5 mg or more does the trick for you) as you take another dose the next day.....all the best, chemist
> chemist
>
> i just read that the "duration of action" for a dose of klonopin is 6-12 hours even though its half-life is longer, and my understanding is that "duration of action" means how long it therapeutically works after you take it
>
> so if my doctor prescribed klonopin for me for GAD, and i take .5mg at 6:00AM, then does that mean it would only work therapeutically until 6:00PM?
>
>
> > > Hi Chemist
> > >
> > > Question: If a tab of Klonopin is taken around 9:00AM, how long would its anti-anxiety effect last? Would taking it just once in the morning (after allowing a week to go by to let it build up to a steady state) be enough to cover the whole day effectively?
> > >
> > > I ask because I'm confused why some people seem to be able to get a full day's anti-anxiety effectiveness from Klonopin by just taking it once-a-day in the morning or at bedtime, while others need to take it 3 times a day in order to get a full day's effectiveness.
> > >
> > > Thanks
> > >
> > hi there....roche states that peak plasma levels of klonopin are reached between 1 and 4 hours after you take it, with elimination half-life between 30-40 hours....for those who are taking klonopin three times a day, they might simply want to decrease the larger ``spike'' - if you will - of taking one dose to three smaller spikes. one must also condsider concurrent meds and dosages. you ask if titrating up for a week and staying at 1 dose per day will work: yes, it should, but how severe is your anxiety and are you prone to panic attacks? if your anxiety is not extreme, then i suspect you can go the once-daily route (provided you get settled-in with the right dose); otherwise, two or three times a day in divided doses. sorry to be so ambivalent about this, but it really varies from person to person....all the best, chemist
>
>
poster:chemist
thread:343522
URL: http://www.dr-bob.org/babble/20040505/msgs/343901.html