Differences in drug responses due to gene alterations are rapidly being identified. Gene alterations may inhibit the function of an enzyme so that an active drug accumulates, causing adverse reactions with normal doses. Alternatively, gene alteration may accelerate enzymatic function so that an active drug is rapidly eliminated, Causing subtherapeutic responses to normal doses. Mutations and polymorpnisms have been identified that affect a person's response to many currently prescribed medications including cardiovascular, anti-infective, chemotherapeutic, psychiatric, and analgesic drugs. The potential exists for drug therapy to be optimized by selecting medication and doses based on a person's genotype rather than by trial and error. In the near future, advanced practice nurses in the acute care setting may be expected to order, provide patient education about, and explain results of genetic tests before initiating a specific drug therapy. Advanced practice nurses must be knowledgeable about what genetic tests are analyzing and their benefits, limitations, and risks.