Objectives Making CYP450, Drug Interactions, & Pharmacogenetics Easy

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1 Objectives Making, Drug Interactions, & Pharmacogenetics Easy Anthony J. Busti, MD, PharmD, FNLA, FAHA Describe the differences between phase I and phase II metabolic pathways. Identify the most common drug metabolizing s. Recall the influx and efflux cell membrane transporters involved in drug distribution and elimination. Describe what a single nucleotide genetic polymorphism is and how it can influence drug efficacy and safety. 2 Outline Background Information Variables That Make Up Drug Interactions The Role of Pharmacogenetics Why is this Topic Important? Every patient is unique: Age Gender Weight Ethnicity and/or Genetics (i.e. pharmacogenetics ) Smoking & Drinking Status Presence of 1 or more disease states in various combinations (especially if they affect renal & liver function) Presence of more than 1 medication to manage most problems 3 4 Why is this Topic Important? We, the healthcare system and medications are DANGEROUS: Institute of Medicine (IOM) Report, To Err is Human: Building a Safer Health System 770,000 hospitalized patients in America alone are likely to experience an adverse drug event (ADE). Prescribing errors per order occurred at rates of 0.6 to 53 per 1,000 orders Errors of omission (i.e. not giving patients necessary and appropriate medications) Institute of Medicine The Literature & Drug Interactions Population Estimate Reference All adults from large HMO Hospitalized patients at time of discharge Veterans Affairs outpatients Elderly patients hospitalized for drug toxicity 3.5% per year for significant DDI 60% had at least 1 DDI; 6.5% were severe 2.15% overall prevalence 14.7 % hospitalized within 1 week of interaction drug addition Solberg et al Egger et al Mahmood et al Juurlink

2 Why is this Topic Important? How do we fix this and become safer? Move beyond fact or guideline driven memorization towards a true scientific and evidenced based understanding of how drugs affect our patients. Institute of Medicine, At the beginning of the medication use process, prescribers often lack sufficient knowledge about how the drugs they are prescribing will work in specific patient populations. If the balance of medication risks and benefits is not known...it is impossible to say whether medication use is safe. Improving medication use and reducing errors, therefore, requires improving the quality of information generated by the pharmaceutical industry and other researchers regarding drug products and their use in clinical practice. Why is this Subject Important? How do we fix this and become safer? Stay up to date on: New Drug Approvals & Indications Drug Alerts, Warnings and News Updates to Treatment Guidelines Continuing education Attend professional conferences & meetings Staying committed to Life Long Learning Institute of Medicine Outline Background Information Variables That Make Up Drug Interactions Metabolism Movement & Distribution Genetic Polymorphisms The Role of Pharmacogenetics Basics of Drug Metabolism Drug Metabolism: Purpose: To make active (or) inactive metabolites Make drug molecules more water soluble for easier elimination Locations: Liver Intestines Kidneys 9 10 Pathways of Drug Elimination Variables in Drug Interactions Biliary Metabolism (Enzyme Pathways) Distribution (Cell Membrane Transporters) Renal Metabolic Phase I (Oxidation/Reduction) Phase II (Conjugation) Influx (Moves Into Cells) Efflux (Moves Out of Cells) 1A2 2C9 2D6 3A4 Glucuronidation Sulfation Acetylation Methylation Glutathione OAT OCT OATPB NTCP BCRP MRP P gp Williams J et al. Drug Metab Disp 2004;32:

3 Pathways of Drug Elimination Esterase FMO UGT 35% Williams J et al. Drug Metab Disp 2004;32: NAT MAO FMO = flavin monooxygenase MAO = monoamine oxidase NAT = n-acetyltransferase UGT = Uridine glucuronosyltransferase 13 Drug Metabolism Phase I Metabolism: Oxidation / Reduction Reactions by s Found in the liver (mainly), intestine, lungs & kidneys. Purpose is for microsomal () s to give/add a functional group to the drug molecule in preparation for phase II metabolism and/or elimination. Those functional groups are: COOH OH NH2 SH Metabolite can be active or inactive 14 Drug Metabolism Phase I Metabolism: s (e.g., 3A4) First number is the Family = 3 The letter is the subfamily = A» The last number is the s in that sub system = 4 Most common: CYP2B6 (3% of meds) CYP2E1 (4% of meds) CYP2C19 (8% of meds) CYP1A2 (11% of meds) CYP2C9 (16% of meds) CYP2D6 (19% of meds) CYP3A4 (36% of meds) Phase I Metabolism Drug A (substrate) Drug A Metabolite 17 18

4 Drug Interactions Drug Interactions Drug B (Substrate) COMPETITIVE (or) REVERSIBLE INHIBITOR Drug A (substrate) Drug B (substrate) COMPETITIVE (or) REVERSIBLE INHIBITOR Drug B Metabolite (vs) Drug A Metabolite Drug A (substrate) Drug B NONCOMPETITIVE Drug A Metabolite Drug Interactions Enzymes & Genetics Drug B = INDUCER Drug A (substrate) Drug A Metabolite Drug A Metabolite In patient with genetic polymorphism to Enzyme Drug A (substrate) Drug A Metabolite Drug A Metabolite Normal functioning Abnormal functioning Phase I (Oxidation/Reduction) 1A2 2C9 2D6 3A4 Variables in Drug Interactions Metabolism (Enzyme Pathways) Phase II (Conjugation) Glucuronidation Sulfation Acetylation Methylation Glutathione Distribution (Cell Membrane Transporters) Influx (Moves Into Cells) OAT OCT OATPB NTCP Efflux (Moves Out of Cells) BCRP MRP P gp Conjugation and Drug Interactions Phase II Metabolism: Conjugation reactions that add a compound to the drug to increase hydrophilicity Almost always inactive metabolites. Glucuronidation (e.g., via UDP glucuronosyltransferases; UGT1A1) Sulfation: sulfotransferases (SULT) Acetylation: N acetyltransferase (NAT) Glutathione conjugation Methylation methyltransferase (MT) 23 24

5 UGT Enzymes UGT1A10 UGT1A3 UGT1A6 UGT1A6 UGT2B7 UGT1A8 UGT1A4 UGT1A1 Williams J et al. Drug Metab Disp 2004;32: Summary of Drug Metabolism Type of Drug Metabolism Type of Reaction Enzyme names Metabolite Most common Phase I Oxidation/Reduction (modifies structure) Active or inactive; less lipophilic or more hydrophilic CYP3A4 Phase II Conjugation (adds a functional group) UGT, SULT, NAT, MT Almost always inactive & more hydrophilic UGT Subject to genetic polymorphisms? Yes Yes Variables in Drug Interactions Metabolism (Enzyme Pathways) Distribution (Cell Membrane Transporters) Phase I (Oxidation/Reduction) Phase II (Conjugation) Influx (Moves Into Cells) Efflux (Moves Out of Cells) 1A2 2C9 2D6 3A4 Glucuronidation Sulfation Acetylation Methylation Glutathione OAT OCT OATPB NTCP BCRP MRP P gp 29 30

6 31 32 Outline Background Information Variables That Make Up Drug Interactions The Role of Pharmacogenetics Genetics Background Human Genome Project completed in 2003 Make up of DNA: Nucleotides: Purines = adenine and guanine Pyrimidines = cytosine, thymine Nucleotides in a specific sequence or order; codon The sequence of nucleotides can influence gene transcription, translation, and/or the final product made (e.g., protein) Every 3 nucleotides (i.e., codon ) code for a specific amino acid which makes up the primary structure of a protein What largely makes us different is due to variations in this sequence. These are what we call SNPs 35 36

7 What is a SNP SNP = single nucleotide polymorphism 1 nucleotide in the sequence of our DNA is changed to another nucleotide. This single change can significantly change the expression of a gene where this change took place or the final product from that gene. How is this notated? E.g., CYP2C19*3 (G636A) W212X Defining a SNP Clinical Application of CYP2C19*3 CYP2C19*3 (G636A) W212X At nucleotide position 636 there is a change in the nucleotide present going from a guanine (G) to adenine (A). This results in a change in the genetic code where the gene would normally place the amino acid tryptophan (W) in position 212 of the amino acid sequence, but now abnormally places a termination sequence of the gene expression at that point. Note the italics in the name vs. CYP2C19 This results in the failure to complete the expression for that gene and thus compromises the final protein product made. In this SNP, CYP2C19 is non functional and this is not active. So what? How cares? Clinical Application of CYP2C19*3 Clinical Application of CYP2C19*

8 Anticoagulants: Warfarin Warfarin Pharmacodynamics: VKORC1 Genetic Characteristics: Located at 16q11.2 5,139 bp Several well known SNPs 44 Warfarin Pharmacodynamics: VKORC1 Warfarin Pharmacokinetics: CYP2C9 Allele SNP Location Activity Expression VKORC1 Wild type 16p11.2 Normal Normal VKORC1*2 C6484T (1173C/T) Intron 1 mrna VKORC1*2 G3673A( 1639G/A) Promoter mrna VKORC1*3 G9041A (3730G/A) 3 UTR mrna VKORC1*3 A8026G Intron 2 mrna VKORC1*4 C6009T Intron mrna Genetic Characteristics: Major Pathway (phase I) for s warfarin: Metabolites: 7 OH warfarin (major) 6 OH warfarin (minor) Minor Pathway for r warfarin via mainly CYP1A1/2, 3A4: Metabolites: 6 OH warfarin 8 OH warfarin 10 OH warfarin Limdi NA et al. Pharmacotherapy. 2008;28(9): Dickman LJ et al. Mol Pharmacol. 2001;60(2): Reider MJ et al. N Engl J Med. 2005;352: Williams PA et al. Nature. 2003;424: Petitpas I et al. J Biol Chem. 2001;276: Warfarin Pharmacokinetics: CYP2C9 Genetic Characteristics: Located at 10q ,720 bp Several well known single nucleotide polymorphisms (SNP) Warfarin Pharmacokinetics: CYP2CP Allele SNP Location Activity Km Vmax CYP2C9*1 Wild type 10q24.1 Normal 28 M 0.22 M CYP2C9*2 R144C (3608C T) Exon 3 CYP2C9*3 I359L (42614A C) Exon 7 CYP2C9*5 D360E (42619C G) Exon 7 CYP2C9* delA (818delA) Exon 5 Null CYP2C9*11 R335W (1003C T) Exon 7 YAC BAC/BAC Chromosome/ideograms/16.html 47 (see drug tables) Limdi NA et al. Pharmacotherapy. 2008;28(9): Dickman LJ et al. Mol Pharmacol. 2001;60(2): Reider MJ et al. N Engl J Med. 2005;352:

9 Abacavir (Ziagen) Abacavir (Ziagen) NRTI for the treatment of HIV infection 8% of patients will experience a hypersensitivity reaction within the first 6 weeks of therapy. Have 2 or more of the following reactions: fever, rash, GI (N/V/D), constitutional symptoms (malaise, fatigue) and/or respiratory symptoms (dyspnea). If it occurs, you must stop abacavir and never use it again. Why do only 8% of patients get this and who is at risk? Abacavir (Ziagen) Abacavir (Ziagen) 51 US Dept HHS Guidelines. Jan. 10, Abacavir (Ziagen) Carbamazepine Marketed Names: Carbatrol Equetro Tegretol Uses/Indications: Epilepsy Trigeminal neuralgia Bipolar disorder 53 54

10 Carbamazepine Side Effects: The most concerning side effect is the development of serious and life threatening skin reactions such as toxic epidermal necrolysis (TEN) and Stevens Johnson Syndrome (SJS). The risk is 10 fold higher in certain people of Asian decent (specifically the Han Chinese; including other countries other than Taiwan) Carbamazepine HLA B*1502 genetic polymorphism: HLA = human leukocyte antigen Class I MHC are found on cells and present antigens to cytotoxic CD8+ T lymphocytes (or Natural Killer cells) If these cytotoxic CD8+ T Lymphocytes see this antigen present by our normal cells as non self then will attack and kill those cells. Prevention: Screen in high risk patients. Treatment: Stop the med, consider admission to burn unit or definitely an ICU. Drug therapy can include: corticosteroids, cyclosporin, or IVIG. Summary Background Information Drug Interactions are a problem Variables That Make Up Drug Interactions Metabolism Phase I = s Phase II = Conjugative s Distribution & Elimination Influx and Efflux Cell Membrane Transporters The Role of Pharmacogenetics 57 58