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Pharmacogenomics and Therapy Dosing

Pharmacogenomics and Therapy Dosing. Tracy Chen Doctor of Pharmacy Candidate 2007 University of Washington September 1, 2006. SOME FACTS AND STATISTICS. Factors to drug responses : Intrinsic factors: age, gender, race/ethnicity, disease states, organ dysfunctions, and genetics

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Pharmacogenomics and Therapy Dosing

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  1. Pharmacogenomics and Therapy Dosing Tracy Chen Doctor of Pharmacy Candidate 2007 University of Washington September 1, 2006

  2. SOME FACTS AND STATISTICS Factors to drug responses: Intrinsic factors: age, gender, race/ethnicity, disease states, organ dysfunctions, and genetics Physiological changes: pregnancy, lactation Extrinsic factors: smoking, diet, concomitant medications Adverse drug reactions (ADRs): Caused 5% of hospitalization Experienced by 10% of the hospitalized patients 700,000 injuries/deaths per year estimated to be the 4th or 6th leading cause of death in the US for the hospitalized patients back at 1998 Huang SM, Goodsaid F, Rahman A, et el. Toxicology Mechanisms and Methods. 2006;(16) 89-99.

  3. SOME FACTS AND STATISTICS 59% of drugs causing ADRs are metabolized by polymorphic enzymes 7-22% of other randomly selected drugs are substrates for polymorphic enzymes Polymorphisms occur in transporters, receptors, and other therapeutic targets are also associated with interindividual variability in drug response. Huang SM, Goodsaid F, Rahman A, et el. Toxicology Mechanisms and Methods. 2006;(16) 89-99.

  4. POLYMORPHIC ENZYMES Cytochrome P450 Enzymes: CYP 2D6 CYP 2C19 CYP 2C9 UDP-Glucuronosyl Transferase: UGT 1A1 TPMT = Thiopurine S-Methyltransferase

  5. CYP2D6 AND CYP2C19 CYP 2D6 in Caucasians: PM: 7% IM: 40% EM: 50% (normal metabolizers) UM: 3% CYP 2C19 in Caucasians: PM: 3% IM: 27% EM: 70% (normal metabolizers) Kirchheiner J, Nickchen K, Bauer M, et el. Mol Psychiatry 2004 May; 9 (5):442-73.

  6. ANTIPSYCHOTICS AND ANTIDEPRESSANTS Psychological disorders are among the most important causes of death and disability worldwide Great impact on public health Only 35-45% of the patients respond to the treatments and return to functional level 30-50% of the patients will not respond sufficiently Kirchheiner J, Nickchen K, Bauer M, et el. Mol Psychiatry 2004 May; 9 (5):442-73.

  7. CYP2D6 AND TCAs TCA dose adjustments are recommended for 2D6 PM and UM. Kirchheiner J, Nickchen K, Bauer M, et el. Mol Psychiatry 2004 May; 9 (5):442-73.

  8. CYP2D6 AND OTHER ANTIDEPRESSANTS Kirchheiner J, Nickchen K, Bauer M, et el. Mol Psychiatry 2004 May; 9 (5):442-73.

  9. 2D6 AND ANTIPSYCHOTICS Antipsychotic dose adjustments are recommended for 2D6 PM and UM. Kirchheiner J, Nickchen K, Bauer M, et el. Mol Psychiatry 2004 May; 9 (5):442-73.

  10. 2C19 AND ANTIDEPRESSANTS Recommendation: 2C19 PM: 60% of standard doses 2C19 EM: 110% of standard doses Kirchheiner J, Nickchen K, Bauer M, et el. Mol Psychiatry 2004 May; 9 (5):442-73.

  11. CYP2C9 20% of hepatic CYP enzymes CYP2C9 *2 allelic frequencies: 10% CYP2C9 *3 allelic frequencies: 8% Anderson T, Flockhart DA, Goldstein DB, et el. Clin Pharmcol Thera. 2005 Dec; 78(6):559-81.

  12. CYP2C9 AND WARFARIN Warfarin is the most common oral anticoagulant in the world The only anticoagulant available in the united states Therapeutic range: INR 2-3 (2.5-3.5 for prosthetic heart valves) INR <2: risk of thromboembolic event INR >3: risk of bleeding complications Mushiroda T, Ohnishi Y, Saito S, et el. J Hum Genet. 2006;51(3):249-53.

  13. Gage B. Nov 14 2005 FDA Clin Pharm Advisor Committe

  14. CYP2C9 POLYMORPHISM Clearance of S-warfarin and time to achieve steady-state (5x T1/2): *1/*1: ~ 3 days *1/*2: ~ 6 days *1/*3: ~ 12 days Linder MW Ph.D. DABCC, Manage the “Over-steer” in warfarin dose titration.

  15. VKORC1 POLYMORPHISM At least 10 different single-nucleotide-polymorphisms (SNPs) were identified • Haplotype A (-1639GA, 1173CT): lower maintenance dose • Haplotype B (9041GA): higher maintenance dose • VKORC1 A/A: 2.7 ± 0.2 mg/d • VKORC1 A/B: 4.9 ± 0.2 mg/d • VKORC1 B/B: 6.2 ± 0.3 mg/d • Mean maintenance dose: 5.1 ± 0.2 mg/d Rieder MJ, Reiner AP, Gage BF, et el. N Eng J Med 2005;352:2285-93. Schalekamp T, Brasse BP, Roijers JF, et el. Clin Pharmacol Ther. 2006 Jul; 80(1):7-12. Herman D, Peternel p, Stegnar M, et el. Thromb Haemost 2006; 95:782-7. Sconce EA, Khan TI, Wynne HA, et el. Blood Oct 2005;106(7):2329-33 Gage BF, MD, MSc. http://www.fda.gov/ohrms/dockets/ac/05/slides/2005-4194S1_04_Gage.ppt

  16. DOSING ALGORITHM 2005PROPOSED Sconce EA, Khan TI, Wynne HA, et el. Blood Oct 2005;106(7):2329-33

  17. DOSING ALGORITHM 2006 PROPOSED Linder MW Ph.D. DABCC, Manage the “Over-steer” in warfarin dose titration.

  18. THERAPY INITIAION • Start with standard induction protocol with 5 mg/d for 3 days • Genotype recommended for both 2C9 and VKORC1 for maintenance dose and clearance (T1/2) estimate • Start with target maintenance dose on day 4 • Measure INR at appropriate time frame, day 3, 6, or 12 for monitoring Linder MW Ph.D. DABCC, Manage the “Over-steer” in warfarin dose titration.

  19. UGT1A1 Homozygous UGT1A1*28 allele with reduced enzyme activity in Caucasian: 10%. Irinotecan carboxylesterase SN-38 (active) SN-38  UDP-glucuronosyl transferase 1A1 (UGT1A1) conjugated inactive metabolite. SN-38 can be metabolized by UGT1A6, 1A7, 1A9, and 1A10 as well. Anderson T, Flockhart DA, Goldstein DB, et el. Clin Pharmcol Thera. 2005 Dec; 78(6):559-81. Camptosar (irinotecan) package insert: http://www.fda.gov/medwatch/SAFETY/2005/Jun_PI/Camptosar_PI.pdf

  20. UGT1A1 SN-38 is associated with neutropenia and life-threatening diarrhea. Patients with homozygous UGT1A1*28 allele are at increased risk for ADRs following the initiation of therapy due to increased level of SN-38. Recommend decrease the starting dose of irinotecan by at least 1 dose level to avoid cytotoxicity for homozygous UGT1A1*28 allele carriers. Camptosar (irinotecan) package insert: http://www.fda.gov/medwatch/SAFETY/2005/Jun_PI/Camptosar_PI.pdf

  21. TPMT TPMT- normal metabolizer (homozygous functional alleles): 90% TPMT- intermediate metabolizer (heterozygous with one nonfunctional allele): 10% TPMT- deficient metabolizer (homozygous nonfunctional alleles): 0.3% Eichelbaum M, Ingelman-Sundberg M, Evans WE. Annu Rev Med. 2006.57:119-137.

  22. TPMT Azathioprine and 6-mercaptopurine are immunosuppressive antimetabolites. Imuran (azathioprine) package insert: http://www.prometheuslabs.com/pi/Imuran.pdf

  23. TPMT The active thiopurine metabolite, 6-TGN, can eventually results in myelosuppresion, a dose limiting factor for therapy. TPMT- deficient metabolizers can have increased level of 6-TGN and are at higher risk for severe, sometimes fatal, myelosuppresion. Eichelbaum M, Ingelman-Sundberg M, Evans WE. Annu Rev Med. 2006.57:119-137.

  24. TPMT Predominantly genotyping or phenotyping for TPMT variant alleles is recommended before thiopurine therapy. TPMT- deficient metabolizers: give 6-10% of the standard dose of thiopurine and monitor CBC carefully. TPMT- intermediate metabolizers: usually start on full dose, but dose reduction is recommended to avoid toxicity. Imuran (azathioprine) package insert: http://www.prometheuslabs.com/pi/Imuran.pdf Eichelbaum M, Ingelman-Sundberg M, Evans WE. Annu Rev Med. 2006.57:119-137

  25. DDI THIOPURINES VS ALLOPURINOL Allopurinol is a xanthine oxidase inhibitor. Give 1/3 -1/4 of the usual dose of azathioprine if patients receive both allopurinol and azathioprine concomitantly. Use further dose reduction or alternative therapies for TPMT- deficient metabolizers receiving both azathioprine and allopurinol. Imuran (azathioprine) package insert: http://www.prometheuslabs.com/pi/Imuran.pdf

  26. ATOMOXETINE VS 2D6 PM ATOMOXETINE VS 2D6 INHIBITORS Cav,ss and AUC of atomoxetine are approximately 10 fold higher in 2D6 PMs than in EMs. The mean T1/2 has increased from 5.2 hours to 21.6 hours. Atomoxetine concentration increases by 3-4 fold when coadministered with paroxetine. Sauer JM, Ring BJ, Witcher JW. Clin Pharmacokinet. 2005; 44(6): 571-90 Strattera (atomoxetine) package insert: http://pi.lilly.com/us/strattera-pi.pdf

  27. ATOMOXETINE Recommend dosage adjustment in CYP2D6 PM and those taking strong 2D6 inhibitors Individual > 70 kg: start at 40 mg/day Individual ≤ 70 kg: start at 0.5 mg/kg/day. *Increase to the usual target dose of 80 mg/day and 1.2 mg/kg/day, respectively, only if treatment fails to improve symptoms after 4 weeks and the initial doses are well tolerated. Strattera (atomoxetine) package insert: http://pi.lilly.com/us/strattera-pi.pdf

  28. CONCLUSION Genotyping recommended for different polymorphic enzymes before initiation of therapies Dose recommendations Improve better therapeutic outcomes Minimizing adverse drug reactions Further studies on ethnicities, pharmacoeconomics, dosing algorithms (prospective) required.

  29. QUESTIONS CYP 2D6? UGT1A1? CYP 2C19? TPMT? CYP 2C9? RXs!!

  30. REFERENCES Anderson T, Flockhart DA, Goldstein DB, et el. Drug-metabolizing enzymes: Evidence for clinical utility of pharmacogenomic tests. Clin Pharmcol Thera. 2005 Dec; 78(6):559-81. (16338273) Camptosar (irinotecan) package insert: http://www.fda.gov/medwatch/SAFETY/2005/Jun_PI/Camptosar_PI.pdf Eichelbaum M, Ingelman-Sundberg M, Evans WE. Pharmcogenomics and individualized drug therapy. Annu Rev Med. 2006.57:119-137. (16409140) Gage BF, MD, MSc. New insights on warfarin: how CYP2C9 and VKORC1 information may improve benefit-risk ratio. http://www.fda.gov/ohrms/dockets/ac/05/slides/2005-4194S1_04_Gage.ppt Huang SM, Goodsaid F, Rahman A, et el. Application of pharmacogenomics in clinical pharmacology. Toxicology Mechanisms and Methods. 2006;(16) 89-99. http://www.fda.gov/cder/genomics/publications/2006_Huang_Cogenomicis_Clin_pharm.pdf Herman D, Peternel p, Stegnar M, et el. The influence of sequence variations in factor VII, gamm-glutamyl carboxylase and vitamin K expoxide reductase complex genes on warfarin dose requirement. Thromb Haemost 2006; 95:782-7. (16676068) Imuran (azathioprine) package insert: http://www.prometheuslabs.com/pi/Imuran.pdf Kirchheiner J, Fuhr U, Brockmoller J. Pharmacogenetics-based therapeutic recoomendations-ready for clinical practice? Nature Aug 2005; (4) 639-647 Kirchheiner J, Nickchen K, Bauer M, et el. Pharmacogenetics of antidepressants and and antipsychotics: the contribution of allelic variations to the phenotype of drug response. Mol Psychiatry 2004 May; 9 (5):442-73. (15037866) Leon, JD MD; Armstrong SC MD; Cozza KL MD. Clinical guidelines for psychiatrists for the use of pharmacogenetic testing for CYP450 2D6 and CYP450 2C19. Psychosomatics. Jan-Feb 2006; 47(1):75-85 Mushiroda T, Ohnishi Y, Saito S, et el. Association of VKORC1 and CYP2C9 polymorphisms with warfarin dose requirements in Japanese patients. J Hum Genet. 2006;51(3):249-53. (16432637) Linder MW Ph.D. DABCC, Manage the “Over-steer” in warfarin dose titration. Presented 08/31/2006 Rieder MJ, Reiner AP, Gage BF, et el. Effect of VKORC1 haplotypes on transcriptional regulation and warfarin dose. N Eng J Med 2005;352:2285-93. (15930419) Sauer JM, Ring BJ, Witcher JW. Clinical pharmacokinetics of atomoxetine. Clin Pharmacokinet. 2005; 44(6): 571-90 (15910008) Schalekamp T, Brasse BP, Roijers JF, et el. VKORC1 and CYP2C9 genotypes and acenocoumarol anticoagulation status: interaction between both genotypes affects overanticoagulation. Clin Pharmacol Ther. 2006 Jul; 80(1):7-12. (16815313) Sconce EA, Khan TI, Wynne HA, et el. The impact of CYP2C9 and VKORC1 genetic polymorphism and patient characteristics upon warfarin dose requirements: proposal for a new dosing regimen. Blood Oct 2005;106(7):2329-33 (15947090) Strattera (atomoxetine) package insert: http://pi.lilly.com/us/strattera-pi.pdf Weinshilboum RM. Pharmacogenomics: catechol O-methyltransferase to thiopurine S-methyltransferase. Cell Mol Neurobiol 2006 Jun 29. (16807786)

  31. Genelex!

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