Posted by ed_uk on August 6, 2005, at 15:17:06
In reply to Re: Oh yay, another single-isomer drug launched in UK, posted by Nickengland on August 6, 2005, at 14:05:06
Hi Nick!
>I was wondering, will this be available over the counter?
Newly licensed products are only available on prescription initially. I do think it's likely that dexibuprofen will be available OTC at some point in the future though.
>What's an (optical) isomer?
Although there are different types of isomers, I was specifically referring to optical isomers in my post.... so that's what I'll tell you about :-)
Many drugs (eg. paracetamol) consist of a single chemical/molecule only. Some drugs however, such as ibuprofen, consist of *two* distinct chemicals/molecules rather than one. The two molecules are *mirror images* of one another. Ibuprofen consists of two chemicals: dexibuprofen (aka S-ibuprofen) and R-ibuprofen. Dexibuprofen is the active drug.
The 'new' drug, dexibuprofen consists of a single optical isomer only. Standard ibuprofen consists of both optical isomers in a 50:50 ratio ie. 50% dexibuprofen and 50% R-ibuprofen.
Dexibuprofen isn't really a new drug as such, it's simply the active component of ibuprofen.
Similarly, citalopram (Cipramil, Celexa) consists of two chemicals: escitalopram (S-citalopram) and R-citalopram. Escitalopram is the active drug: it's now sold on its own under the brand name Lexapro (Cipralex in the UK). R-citalopram appears to be relatively inactive. Although the manufacturer claims that Lexapro is more effective and better tolerated than Celexa, there is no good evidence to support this claim.
Celexa consists of 50% escitalopram and 50% R-citalopram. Lexapro is 100% escitalopram. Since R-citalopram is (probably) inactive, 20mg Celexa has the same antidepressant effect as 10mg Lexapro.
Drug companies like to develop single-isomer drugs because it can be very profitable. Celexa is now available as a generic whereas Lexapro is not. Lexapro is $$$$
In cases where one optical isomer of a drug is therapeutically active and the other is toxic, separating the isomers is very valuable. In other cases, where one optical isomer is active and the other is inactive, separating the isomers is of no medicinal value: think Lexapro $$$. In most cases, the therapeutically active isomer is also the isomer which causes the side effects! It's a shame that the drug companies are putting so much effort (money) into developing pointless single-isomer drugs when they could instead be developing new and innovative drugs with novel mechanisms of action.
Kind regards
~ed
poster:ed_uk
thread:537977
URL: http://www.dr-bob.org/babble/20050803/msgs/538334.html