@Pandora and @geeky_mama salbutamol (what we call albuterol in the UK) is still the number one drug for the treatment of asthma over here in the UK. Levosalbutamol (Xopenex) is actually quite a controversial drug as chemically speaking it is identical to salbutamol. Any chemical that includes a carbon atom with four different atoms connected to it can be put together in two different ways – mirror images of themsleves like your left and right hands. If you make the molecule in a lab you will end up with a 50/50 mix of the two different vesions however when an living cell puts these types of molecules together they will always make the same version. The two different vesions will behave identically in the lab but in a living organism they will sometimes behave very differently. For example one version of the molecule for Spearmint tastes minty while the other tastes of nothing. From the point of view of medicines the difference between these two different vesions is some time critically important. One version of the molceule for thalidiomide is an extremely effective treatment for nausea and morning sickness however the version causes massive birth defects. Naproxen is another good one – one version is a powerful pain reliever and the other version does nothing but cause heart damage so its important that companies making Naproxen make the right version. Sometimes, however, pharmaceuticalcompanies will try to exploit this so as to maintain a patent on a drug after it has expired. Eosomprazole, for example, is chemically identical to omeprazole however because it is just one version of the molecule they charge a lot more for it despite the fact there is little evidence that it is more effective than omeprazole for treating GERD.
hope this makes sense