A few individuals respond to drugs in a highly unusual and unpredictable manner, giving a response quantitatively much different than in the average patient.
[wp_ad_camp_5]For example some patients may have an intense response to a very small dose of the drug, whereas others may not respond to very high doses. The response may also be qualitatively different in some situations, with new pharmacological effects being observed. Such responses, referred to as drug idiosyncrasy or idiosyncratic response, are infrequent and believed to result from a genetically determined metabolic or enzyme deficiency that is not expressed under normal situations. These responses show a dose–response relationship, but not the same one shown by the average patient.
Example of idiosyncrasy: Hemolytic anemia occurring in patients with glucose-6-phosphate dehydrogenase deficiency after receiving an oxidant drug.