how are chiral drugs separated into their enantiomers?

Answer 1

Because the purity of chiral drugs is controlled by law and the separation of chemical enantomers will cut total yields by at least 50%, the usual solution is to prepare the drug using chiral chemistry so that only the active enantiomer is produced.

There are several techniques wich can be used but most are based upon enantioselective chemical technology used during the synthesis and not separation after production.

Older techniques which require chiral sepatations almost always use chiral chromatography or chiral precipitation.

Answer 2

Either from chiral chromgraphy or chiral chiral precipitation. These are the 2 most commany used methods used by companies today.
Although today synthesis are design to limit the production of of enantionmers forming in production these mostly use other chiral agents, these then leads to the problem of how do I separate those compounds. In some cases the use of a chiral regant in this stage is not even cost effected and hence separation after process is needed.

In the later a chiral ageant that will react with one form is added to the mixture, this causes one chiral form to crystillize out and plus leaves the other one in solution. Such a method is used in the large scale synthesis of paroxtine.