Psychotropic drug responses polymorphism

Ethnic differences have been shown to influence response to psychotropic medications. Much of the focus on the explanation for such differences has been on drug-metabolizing (CYP) enzymes of the liver and their sway over pharmacokinetic factors. It is now well recognized that differences in the distribution of polymorphic variants of CYP enzymes exist between different ethnic groups. However, within ethnic groups there are considerable inter-individual variations in drug kinetics, which may not be accounted for solely by genetic variation. Responses to pharmacotherapy are multifaceted and involve the interaction of environmental and... 

Dextromethorphan is metabolized to dextrophan (Figure 34-40) by the cytochrome P4S0 isozyme 2D6 (GYP 2D6), which exhibits genetic polymorphism. Dextrophan also lacks analgesic activity, but it does retain antitussive action. Dextrophan may be responsible for the more pleasant psychotropic effects of high dose dextromethorphan, whereas the parent drug may cause dysphoria, sedation, and ataxia. Thus poor metabolizers (deficient in GYP 2D6 activity) may be less prone and extensive metabolizers more prone to continue the abuse of dextromethorphan. 

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