Quick Review of Pharmacokinetic-Based Drug
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Awareness of drug interactions increasing in patients with cancer Drug Interactions in Stem Prevalence in HSCT patients Cell Transplantation unknown 4.5-58% in cancer patients Numerous electronic databases exist with variable reliability Jeannine McCune, PharmD, BCOP Electronic systems and alerts are University of Washington promising, but have challenges Fred Hutchinson Cancer Research alert fatigue Center Lemachatti et al. Anticancer Res. 2009 Nov;29(11):4741-4 ; van Leeuwen Ann Oncol. 2011 Oct;22(10):2334-41. Epub 2011 Feb 22. Scott et al. J Am Med Inform Assoc. 2011 Nov-Dec;18(6):789-98 When is a drug interaction in HSCT Learning objectives recipients important? Explain the common metabolic pathways Many potential drug interactions in the liver Type of interactions Identify approaches to overcome drug Pharmaceutical interactions seen in HSCT Incompatibilities at administration site Pharmacokinetic Identify those drug interactions of importance What the body does to the drug Understand how to preemptively prevent drug Pharmacodynamic interactions from occurring What the drug does to the body HSCT interaction example: live vaccines Important if leads to an undesired outcome, whether it be ↓ efficacy or ↑ toxicity The challenges unique to HSCT Quick review of patients are ….. pharmacokinetic-based The concentration-effect (i.e., pharmacodynamic) relationships are drug interaction basics rarely defined Degree of an interaction (and thus its significance) rarely described Drug metabolizing enzymes Cytokines influence regulation Drug transporters Interpatient variability in the interaction When an adverse drug interaction occurs, we often lack the pharmacokinetic data to explain it Relationship between pharmacokinetics and pharmacodynamics Pharmacology is multifactorial Dose Can affect both the pharmacokinetics and Absorption pharmacodynamics Distribution Factors include… Metabolism Excretion Age Total serum concentration Receptor Site Sex Ethnicity Unbound serum concentration Pharmacologic Weight Response Condition being treated Protein Bound Concentration Pharmacogenetics Therapeutic Idiosyncrasy Outcome Drug interaction Slide courtesy of Gail Anderson, PhD Pharmacokinetic parameters: Pharmacokinetic parameters elimination Absorption Metabolism The rate at which a drug leaves the site of Predominately liver administration and the extent to which it occurs Other sites: kidney, lung, gastrointestinal tract (GI), plasma HSCT interaction example: proton pump inhibitors with mycophenolate mofetil HSCT interaction example: many Distribution Excretion Process of reversible transfer of a drug to and Kidneys and hepatic/GI tract from the site of measurement Other sites: milk, sweat, saliva, tears HSCT interaction example: non-steroidal anti- HSCT interaction example: cyclosporine with inflammatory drugs (NSAIDs) with methotrexate (also interacts at kidney) mycophenolic acid Biotransformation (Metabolism) Phase I metabolism Theory Oxidation, reduction, hydrolysis Drug inactivation Cytochrome P450 family of enzymes Increased elimination from the body 7 primary enzymes responsible for majority of Reality drug metabolism Metabolites may have biological activity; Can predict drug interactions based on similar or different than parent knowledge of metabolizing enzymes Various family, subfamily, individual genes May contribute to toxic and/or beneficial effects CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4/5 Example: Cyclophosphamide metabolized by cytochrome P450 (CYP) to Inhibition CYP, concentration, dose 4hydroxycyclophosphamide Induction CYP, concentration, dose Cytochrome P450 (CYP) enzyme system Examples of important CYP in HSCT Large (but not only) source of drug interactions Drug Substrate Reaction Many in vitro methods to identify which Cyclosporine 3A4/5 Elimination CYP metabolizes a drug, and potential drug Tacrolimus 3A4/5 “ interactions Sirolimus 3A4/5 “ Prednisone 3A4/5 “ However, magnitude of drug interaction Dexamethasone 3A4/5 “ difficult to predict Cyclophos- 2C9, 2C19 Activation to 4hydroxyCY (HCY) ‘Cocktail’ studies in healthy volunteers phamide (CY)2 2B6, 3A4/5* Cytokines (e.g., IL6) affect CYP 3A4/5 Detoxification to dechloroCY Hebert. Metabolic Drug Interactions 2000; Shimada Transplant International 2003. Ren Cancer Research 1997; Huang Biochem Pharmacol 2000; Qiu Clin Pharm Ther 2004 Phase II metabolism Phase II: Relevant conjugation reactions Glutathione S-transferase Term coined to represent metabolism Mediate conjugation of electrophilic occurring after oxidation, reduction or compounds to glutathione hydrolysis associated with bioactivation Important detoxifying pathway for alkylating Many drugs don’t require Phase I metabolism agents Functional group created conjugated to less Glucuronidation toxic or inactive compound Most common conjugation reaction for drugs UGT (UDP-glucuronosyl transferase) Conjugation of endogenous substances, bilirubin, mycophenolic acid, morphine ABC transporters relevant to HSCT Drug transporters patients Of the 400 transporters in the human Transporter Substrate genome, 30 are relevant to ABCB1 (MDR1)* calcineurin inhibitors, sirolimus pharmacokinetics corticosteroids ATP-binding cassette (ABC) superfamily ABCC1 (MRP1) methotrexate ABCC2 (MRP2) cyclophosphamide metabolite Relevant to systemic pharmacokinetics and mycophenolic acid intracellular transport ABCC3 methotrexate ABCG2 (BCRP) etoposide, topotecan *codes for pglycoprotein (pgp) Endres et al. Eur J Pharm Sci. 2006 Apr;27(5):501-17 Additional transporters Excretion Organic anion transporting polypeptide (OATP) Drugs are eliminated from the body methotrexate, opioids, corticosteroid metabolites unchanged or as metabolites Organic anion transporters (OAT) Complex, for example renal excretion beta-lactams, metabolites of corticosteroids, NSAIDs involves Equilibrative nucleoside transporter 1 (ENT) Glomerular filtration fludarabine Concentrative pyrimidine-preferring nucleoside Active tubular transport transporter 1 (CNT) Passive tubular absorption fludarabine HSCT interaction example: NSAIDs inhibit renal tubular secretion of methotrexate and/or reduce renal blood flow by Zhang et . Clin Pharmacol Ther. 2011 Apr;89(4):481-4; Pauli-Magnus Pharmacogenetics 2003; 13: 189; Sekine Annals of Oncology 2001; 12: 1515; Oleschuk Am J Physiol Gastrointest Liver Physiol 2003 inhibiting prostaglandin synthesis Feb;284(2):G280; Elimination half-life Pharmacokinetic parameters Example: Plasma Concentrations Drug with T1/2 = 12 hrs Clearance measures body’s ability to Dose 100 mg 200 mg eliminate drugs Elimination half-life is time it takes for the C0 20 g/ml 40 g/ml amount of drug in the body to be reduced by C 10 g/ml 20 g/ml 50% 12hr C 5 g/ml 10 g/ml T1/2 = 0.693•Vd 24hr Cl C36hr 2.5 g/ml 5 g/ml where Vd = volume of distribution and Cl = total body clearance C48hr 1.2 g/ml 2.5 g/ml Impact of CYP interactions on clearance C60hr < 1 g/ml 1.2 g/ml Inhibition CYP, clearance, concentration, dose Induction CYP, clearance, concentration, dose C72hr < 1 g/ml < 1 g/ml Slide courtesy of Gail Anderson, PhD Approximate half-lives of relevant Steady state immunosuppressants Css = the concentration at which the rate Calcineurin inhibitors: 11-35 hours (hr) of drug input is equal to the rate of drug elimination Sirolimus: 62 hr Can be defined as area under the curve/dosing interval (busulfan) Mycophenolic acid: 0.6-11.9 hr Takes approximately 5 T1/2 to reach steady state Methylprednisolone, prednisone: 1.7 to 4.1 hr Take approximately 5 T1/2 to completely eliminate a drug after discontinuation Css is dependent on dosage and clearance Learning objectives Explain the common metabolic pathways in the liver GVHD Medications Identify approaches to overcome drug interactions seen in HSCT Identify those drug interactions of importance Cyclosporine, Tacrolimus, Understand how to preemptively prevent drug Sirolimus, Methotrexate, interactions from occurring Mycophenolate mofetil, Corticosteroids Less commonly used GVHD medications The interactions discussed Immunomodulating modalities mTOR- Pharmacokinetic interactions relevant to GVHD inhibitors, thalidomide, prophylaxis and treatment Will discuss herbal preparations, but recall they are hydroxychloroquine, vitamin A analogs, unique because of potential pill to pill variability in content, for fungal contamination, immunologic rituximab, alemtuzumab, etanercept properties….. Cytostatic agents: cyclophosphamide, Omitting others not because they are less pentostatin important but they may be more easily identified (e.g., the opioids because of close concentration – effect relationship) more broad therapeutic index of the medication (e.g., most antibiotics) Pidala BBMT 2011, 17(10):1528; 2Ferrara Lancet 2009, 373: 9674; Holler Best Pract Res Clin Haematol. 2007 Jun;20(2):281-94, Wolff BBMT 2011;17(1):1-17 Effect of food/herbs Calcineurin inhibitors (CNI) Effect Cyclosporine (CyA) and tacrolimus (TAC) Grapefruit juice intestinal CYP3A, pgp Considerable pharmacokinetic variability in CNI St. John’s wort CYP3A4, pgp concentrations obtained in patients receiving Garlic CYP3A4 same dose CNI concentrations related to clinical Difficult to know magnitude of problem outcomes (pharmacodynamics) Difficult to predict CyA/TAC risk of acute GVHD Expect grapefruit juice to ↑ absorption of etoposide, a CYP3A/pglycoprotein substrate, but it actually ↓ CyA/TAC nephrotoxicity