Genetic factors in drug metabolism

Omeprazole 20 mg daily for 8 days had no effect on the pharmacokinetics of phenacetin, or paracetamol derived from phenacetin, in 10 healthy subjects, except that the peak plasma level of phenacetin was higher. There was no change in the metabolism (oxidative and conjugative) of phenacetin or derived paracetamol. In another study, omeprazole 40 mg daily for 7 days had no effect on the formation of thioether metabolites of paracetamol in 5 rapid and 5 slow metabolisers of 5-mephenytoin [a probe drug for CYP2C19 activity, see Genetic factors in drug metabolism , (p.4)].3... 

Quinidine inhibits the oxidative metabolism of dextromethorphan by the eytochrome P450 isoenzyme CYP2D6 to dextrorphan, effeetively making extensive metabolisers of CYP2D6 into the poor metaboliser phenotype, see Genetic factors in drug metabolism , (p.4), for further discussion of metaboliser phenotypes. 

Genetic factors Several drug-metabolizing systems have been shown to differ among families or populations in genetically determined ways. 

Breimer DD (1994) Genetic polymorphisms in drug metabolism clinical implications and consequences in ADME studies. In Walker S, Lumley C, McAus-lane N (eds) The relevance of ethnic factors in the clinical evaluation of medicines. Kluwer Academic Publishers, Dordrecht... 

Not all patients are the same. Patients differ in their age, gender, genetics, and health. All these factors can play a role in drug metabolism. Metabolism rate is evaluated through the basic pharamacokinetic parameters of Vd, CL, kel, and tl/2 (Chapter 7). Of course, to show variability in metabolism, a drug must first be metabolized. Some drugs are eliminated unchanged. 

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