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Pharmacogenetics: Integration into new drug development Academic Perspective. David Flockhart MD, PhD Indiana University School of Medicine . Steps Toward Clinical Pharmacogenetic Labelling. Response. Response. Genetic Variant No Yes.
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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.