Posted by dr dave on September 4, 2002, at 15:12:33
In reply to Re: Raines et al/see bottom » Patson, posted by pharmrep on September 3, 2002, at 0:58:11
You have mentioned the Sanchez paper which shows Lexapro raising brain serotonin more than an equivalent dose of Celexa. This seems to show r-citalopram impeding the action of s-citalopram.
But there is another side to this. Another paper by Sanchez compares the potency of Lexapro and Celexa. The results are in terms of IC50 - the concentration required to inhibit serotonin re-uptake by 50%.
2.1 nM of Lexapro inhibits re-uptake by 50%, whereas 3.9 nM of Celexa is required. So Lexapro is about twice as potent. But let's think about this. Once Celexa is absorbed, you end up with 36% s-citalopram and 64% r-citalopram in the circulation. So the concentration of s-citalopram needed to achieve 50% inhibition, when r-citalopram is also present, is 36% of 3.9nM - only 1.4nM!
So from these results, r-citalopram helps s-citalopram with serotonin re-uptake inhibition! This is pretty definitely not true, but it demonstrates how unreliable individual results can be, and if you pick out the right results you can make them say all sorts of improbable things. This is why I feel it is so important to look at all the data.
I think we should be able to examine the trials which have been done comparing Celexa and Lexapro. Currently (as far as I am aware) the comparisons from only one of three trials has been disclosed (Burke et al). The study written up by Lepola et al and Montgomery et al has had the citalopram data removed, for no apparent reason. The third trial has not been disclosed at all.
I think we should be able to have access to all the information so we can make up our own minds.
poster:dr dave
thread:109458
URL: http://www.dr-bob.org/babble/20020829/msgs/118800.html