What type of drug contains only a single enantiomer?

An enantiopure drug is one that consists entirely of a single enantiomer, meaning it only contains one chiral form of a molecule, without the presence of its mirror image. This is significant in the field of pharmacology because the two enantiomers of a chiral drug can have different effects in the body. One enantiomer may be therapeutically active, while the other could be inactive or even cause adverse effects. Therefore, enantiopure drugs can often offer more predictable and effective therapeutic outcomes compared to mixtures that contain both enantiomers.

Racemic mixtures, on the other hand, contain equal parts of both enantiomers, which can dilute the therapeutic effect of the active enantiomer. Generic drugs refer to medications that are chemically identical to branded drugs and may be available as a racemic mixture or as an enantiopure formulation, depending on the original compound. Combination drugs consist of two or more active ingredients, which may or may not be enantiomers, but do not fit the definition of containing solely a single enantiomer. Thus, the presence of only one enantiomer characterizes an enantiopure drug, making it the correct answer.