The document discusses using genetic testing to guide warfarin therapy. It explains that genetic polymorphisms affect individuals' responses to medications like warfarin. Variants in CYP2C9 and VKORC1 genes influence warfarin dosing, with clinical trials showing genotype-guided dosing results in faster stabilization of anticoagulation and less risk of bleeding events. The author proposes a study at UNC to incorporate pharmacogenomic guidance in initial warfarin dosing to improve outcomes.

1. Pharmacogenomics: Using Genetic Testing to Guide Warfarin Therapy Dan Jonas, MD, MPH Noon Conference October 29, 2007

3. Single Nucleotide Polymorphisms (SNPs) A key to human variability DNA sequence variation at a single nucleotide that may alter the function of the encoded protein Polymorphisms are common and contribute to common diseases and influence our response to medications * Functional but altered protein Functional protein

7. Goldstein DB, et al. Nature Reviews 2003;4: 937-947 Genetic variants found to be significantly associated with drug response in at least two studies Nature Reviews 2003;4:937-947

8. Goldstein DB, et al. Nature Reviews 2003;4: 937-947 Genetic variants found to be significantly associated with drug response in at least two studies Nature Reviews 2003;4:937-947

18. Effect of VKORC1 Haplotype A or B on Warfarin dosage Rieder et al. New England Journal of Medicine 2005

19. Individual Variability in Warfarin Dose Warfarin maintenance dose (mg/day) SENSITIVITY CYP2C9 coding SNPs RESISTANCE VKORC1 coding SNPs Frequency Common VKORC1 non-coding SNPs Adapted from Rettie and Tai, Molecular Interventions 2006 (*3/*3) 0.5 5 15

29. Experimental Group Pharmacist calculates dose using algorithm ASAP without genetic info & re-calculates dose including genetic info as soon as available Pharmacist communicates recommended dose to the treating physician & ensures patient is d/c’d on that dose Pharmacist calculates dose using algorithm ASAP without genetic info Clinical pharmacist makes dose change Subjects follow up for routine care in the ACC or Family Medicine Center Anticoagulation Clinc Control Group Collect outcomes data over first 3 months of treatment: visits, TTR, utilization… Pharmacist communicates recommended dose to the treating physician & ensures patient is d/c’d on that dose Clinical pharmacist makes dose change Subjects follow up for routine care in the ACC or Family Medicine Center Anticoagulation Clinc Collect outcomes data over first 3 months of treatment: visits, TTR, utilization…

35. EXTRA SLIDES

37. CYP2C9 Polymorphisms (*2) Arg  Cys codon 144 (*3) Ile  Leu codon 359 (*4) Ile  Thr codon 359 (*5) Asp  Glu codon 360 (*1) wild type

41. CYP2C9 gene variants Enzyme Activity Normal Reduced (50-70%) Reduced (5-15%) I359L * R144C * CYP2C9*1 (wild type) CYP2C9*2 CYP2C9*3

42. CYP2C9 Allele frequencies Absent? Rare 0.023 *11 (R335W) Absent? Absent? 0.01 *6 (818delA) Absent? Absent? 0.01 *5 Absent? Absent? 0.01 *4 0.02-0.4 0.05-0.10 0.01 *3 Rare 0.10-0.16 Rare *2 0.984 0.743 0.953 *1 Asians Caucasians African Americans

43. VKORC1 gene variants Enzyme Clinical Activity Effect spontaneous bleeding (VKCFD2) Warfarin Warfarin resistance binding? OR OR Warfarin dose R98W *  SNPs

44. Percent of warfarin dose variability explained by CYP2C9 and VKORC1 *Total variability explained by genetic, demographic and clinical variables Clinical and demographic factors alone explain 20-25% of dose variability 60% 52% 34% 18% 14 54% 37% 24% 13% Avg 59% 30% 13% 17% 12 21% 18% 34% 21% 25% VKORC1 26% 33% 44% 41% 32% Gx total 39% 5% 13 57% 10% 9 45% 15% 11 63% 20% 8 51% 7% 7 55% 1 Total* CYP2C9 Ref

46. Warfarin dosing algorithm (based on age, height, CYP2C9 and VKOR) Sconce, et al. Blood 2005

50. CYP2C9 7-hydroxywarfarin 6-hydroxywarfarin 8-hydroxywarfarin 10-hydroxywarfarin CYP1A1 CYP1A2 CYP3A4