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Explore steps towards clinical pharmacogenetic labeling response, ideal parameter separation, identifying genetic variants, and the role of Genetically Polymorphic Cytochrome P450 Isoforms. Learn about CYP2D6, its metabolic activities, and recommendations for defining useful pharmacogenetic tests.
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Pharmacogenetics: Integration into new drug developmentAcademic Perspective David Flockhart MD, PhD Indiana University School of Medicine
Response Response Genetic Variant No Yes
Ideal Parameter Separation: Relative Risk is large RR Yes This Never Happens Response No No Yes Genetic Variant
Number needed to test? Absolute Risk? Relative Risk? P < 0.05? Yes Response No No Yes Genetic Variant
Genetically Polymorphic Cytochrome P450 Isoforms • CYP1A2 • CYP2B6 • CYP2C8 • CYP2C9 • CYP2C19 • CYP2D6 • CYP3A5
Cytochrome P450 2D6 • Absent in 7% of Caucasians • Hyperactive in up to 30% of East Africans • Catalyzes primary metabolism of: • codeine • dextromethorphan • metoprolol • tamoxifen • tricyclic antidepressants • Inhibited by: • fluoxetine • haloperidol • paroxetine • quinidine
120 1011 Subjects 80 Number of Subjects EMs PMs UMs 40 cutoff 0 0.01 0.1 1 10 100 Debrisoquine/4-Hydroxydebrisoquine Metabolic Ratio CYP2D6 Pharmacogenetics
60 0 1 30 2 3 13 Nortriptyline: 2 allele patients had greater clearance than 1 or 0 allele patients. Number of functional CYP2D6 genes Plasma concentration/25 mg dose (nmol/L) 0 0 24 48 72 Hours
Paroxetine : 1 deficient allele can distinguish from EMs Shin J-G et al: CPT 2000;67:567-576.
Doses of nortriptyline recommended for different CYP2D6 phenotypes and genotypes in Europe.
Recommendations • Define and make clear a disease-specific parameter that is a target for a useful pharmacogenetic test. • For CYP2D6, CYP2C19 and CYP2C9 recommend a genotype and phenotypic test that define the “intermediate metabolizer” group.