text: The eutomer is the enantiomer having the desired pharmacological activity, e.g.,  as an active ingredient in a drug.
  The distomer, on the other hand, is the enantiomer of the eutomer which may have undesired bioactivity or may be bio-inert.
  A racemic mixture is an equal mixture of both enantiomers, which may be easier to manufacture than a single enantiomeric form.
  It is often the case that only a single one of the enantiomers contains all of the wanted bioactivity, the distomer is often less active, has no desired activity or may even be toxic. In some cases, the eudysmic ratio is so high, that it is desired to separate out the two enantiomers instead of leaving it as a racemic product. It is also possible that the distomer is not simply completely inactive but actually antagonizes the effects of the eutomer. There are a few examples of chiral drugs where both the enantiomers contribute, in different ways, to the overall desired effect. An interesting situation is that in which the distomer antagonizes a side-effect of the eutomer for the desired action, mutually beneficial action form therapeutic standpoint.  This is convincingly demonstrated by the diuretic indacrinone. 
  The (R)-(+)-isomer, the eutomer, is responsible for the diuretic action and undesired uric acid retention, a side-effect common to many diuretics.  The (S)-(-)-isomer, the distomer, acts as a uricosuric agent and thus antagonizes the side-effect caused by the (R)-isomer.  A superficial examination of these facts might suggest the marketing of this product as a racemate (1:1 mixture of both enantiomers) to be desirable, since both enantiomers are complementing each other, but for optimal action, the ideal eutomer to distomer ratio for indacrinone has been determined to be 9:1.  This is a classical case of a non-racemic drug. Alternatively, it is possible that in the body the distomer converts, at least in part, into the eutomer.