Posted by Larry Hoover on June 14, 2003, at 23:05:30
In reply to St.JAMES: HELP! Need some DEFINITION assistance!, posted by Janelle on June 13, 2003, at 20:23:12
> I'm determined to be able to understand the difference between Lexapro and Celexa, the latter of which I'm on, and I just know it boils down in large part to the "enantiomer" differences between the two meds, but I can't get a grip on what the r and s enantiomers are! Thanks.I missed the significance of your question in the context of Celexa and Lexapro, so I'll expand on that a little bit.
When human being synthesize drugs, if a chiral center is involved, you typically get something like a 50-50 mix of the two enantiomers, the r- and s- forms. That's just because we don't have the elegant machinery of living organisms, which don't waste energy making unusable forms, as biological enzymes are designed to produce one enantiomer exclusively. In a chemist's reaction flask, molecules form by random processes, and the products are statistical, like flipping a coin.
Man made mixes of the two enantiomers are called racemates. Many drugs are sold that way, if the clinical trial shows them to be effective and there are reasonable levels of side effects. Sometimes one enantiomer is profoundly toxic, as was found with thalidomide. One enantiomer causes birth defects; the other is perfectly safe during pregnancy. (In any case, it will never again be given to pregnant women, you can be sure. Pharmaceutical companies don't like political suicide moves.) Still, it is an effective drug against leprosy and tuberculosis, and some cancers.
In today's profit driven pharmaceutical industry, any change in the patented molecule permits the registration of a new patent (and the exclusive rights for all those years that go along with the new patent). If you can come up with an argument that an entiomeric purification changes the pharmacology of the drug, then that is considered to be a pharmacological change arising from a chemical change (even though there is no chemical change, in a literal sense). So, clinical trials of the purified s-enantiomer (escitalopram) provided sufficient evidence of different pharmacology (lower dose for same response, and decreased side effects), convincing the FDA to register it as a new drug, with a new patent.
I take the cynic's view. It was never about purifying the drug, and reducing side effects. It was about getting an extended market monopoly on a commercially successful drug, with much reduced development costs (amortized over the combined marketing life-time of the drug racemate and enantiomers).
Another example is the GERD/reflux drug Prilosec/Nexium (omeprazole/esomeprazole). Same drug, racemate and single enantiomer. Major profits on Nexium.(I took part in the clinical trial on Nexium. They violated certain terms of the protocol with me, and I have yet to receive a satisfactory response to my inquiries. On request, they are to unblind the data at conclusion, and provide detailed outcomes for any subject so requesting data.)
If Celexa's working for you, there is no justification to switch to Lexapro. Just because the pharmaceutical company argued that the r-enantiomer was either inert or even toxic, doesn't mean that it is so, for you (or anybody, for that matter). I just don't trust the clinical trial process too much. Clinical trials are not done by independent researchers. The drug companies do their own trials. No vested interest in the outcome there, right?
Lar
poster:Larry Hoover
thread:233801
URL: http://www.dr-bob.org/babble/20030614/msgs/234067.html