Drug Metabolism. Importance of Drug Metabolism. Importance of Drug Metabolism. Prof. Patrick Davis Basic Medicinal Chemical Principles

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1 Drug Metabolism Prof. Patrick Davis Basic Medicinal Chemical Principles PR 143M Fall-08 The basic premise: Lipophilic Drugs --> ydrophilic Metabolites (ot Excreted) (Excreted) Water soluble => increased renal excretion -anddecreased tubular re-absorption of lipophilics. C 2 C C Δ 1 -TC PC=6000 C 2 5 Excreted Form C - C C 2 5 1

2 Metabolism => Termination of Drug Action Bioinactivation -and/or- Detoxification -and/or- Elimination -and/or- Metabolism => Termination of Drug Action Bioinactivation C 2 2 C C 2 C 2 Procaine C 2 2 C 2 C C 2 C 2 C 2 Metabolism => Termination of Drug Action Detoxification Disulfiram (Atabuse ) C C C C 2

3 Metabolism => Termination of Drug Action Elimination (water soluble). C C + C Acetaminophen - ulfate - C Glucuronide Metabolism => Termination of Drug Action Bioinactivation -and/or- Detoxification -and/or- Elimination -and/or- Metabolism => Bioactivation Active Metabolites Prodrugs Toxification 3

4 Metabolism => Bioactivation Active Metabolites (urprise! :) (C 2 ) 3 Imipramine (C 2 ) 3 Desipramine Metabolism => Bioactivation Prodrugs (by Design!) F C 2 C F C 2 C ulindac (Prodrug) ulindac ulfide (Active) Metabolism => Bioactivation Toxification ( toxigenic metabolism; ops!) + + MPTP MPDP MPP+ (eurotoxin) 4

5 Metabolism => Termination of Drug Action Bioinactivation -and/or- Detoxification -and/or- Elimination -and/or- Metabolism => Bioactivation Active Metabolites Prodrugs Toxification Metabolism => Drug Interactions Warfarin (Anticoagulant) P-450 Metabolite(s) (Inactive) Chloramphenicol (Antibiotic) Is This Just ype? 3 C 2 Azathioprine (Imuran ) 6-Mercaptopurine (Active) Xanthine xidase 6-Thiouric Acid (Excreted) 5

6 ow Real Is This? 3 C 2 Allopurinol Xanthine xidase Azathioprine (Imuran ) 6-Mercaptopurine (Toxic) Allopurinol Colchicine Corticotropin Ibuprofen Prednisolone Prednisone Probenecid odium Thiosalicylate ulfinpyrazone Triamcinolone tereochemical Implications of Metabolism C -Ibuprofen (Active) C R-Ibuprofen (Inactive) tereochemical Implications of Metabolism R C -Benoxaprofen (Active) raflex Elderly R C R-Benoxaprofen (Inactive) Toxicity R = p-chlorophenyl 6

7 Control of Metabolism Through Drug Design If you can predict metabolic pathways => Avoid toxigenic pathways. cytotoxicity, carcinogenicity, mutagenicity risk assessment (drug development) acute vs long-term therapy peed up metabolism?? Why?? low down metabolism?? Why?? Review Termination of Drug Action Bioactivation Drug Interactions tereochemical Implications Control of Metabolism Absolutely Required by FDA Clearly affects efficacy Clearly affects toxicity Understanding It Practice problems: Foye s Med. Chem. Liver Game (class exercise). nline Practice Quizzes.* [Do Pre-Test ow] Previous Exams (view as practice problems).* Flash Metabolism Tutorials* Blackboard Discussion Board; ffice ours; effice ours* Concept Map Lab *[ or UTDirect] 7

8 Drug Metabolism References Foye s Principles of Medicinal Chemistry,, 6th Edition (2007), Chapter 10 (Drug Metabolism) [your required text]. Goodman & Gilman Pharmacological Basis of Therapeutics, 11th Edition (2005), Chap 3 (Drug Metabolism) [your required text]. nline references [Blackboard website] PRACTICE DRAWIG PATWAY! Phase-1 vs. Phase-2 Metabolism Prof. Patrick Davis Basic Medicinal Chelmistry Principles PR 143M Fall-08 Phase-1 Metabolism Description Phase 1 = "Functionalization" Reactions ew polar functional groups. Interchange existing functional groups Unmask existing polar groups. 8

9 Phase-1 Metabolism Description Reactions include: xidations (hydroxylations) = new R --> R Reductions = interconversion C= --> C- ydrolyses = unmasking R-C 2 --> RC + Phase-1 Metabolism Description Purpose: enhance excretion R --> R (more water soluble) prepare for phase 2 R --> R (functional handle) Phase-2 Metabolism Description Phase 2 = "Conjugation" Reactions Acts on parent drug or Acts on phase 1 metabolite. Links to endogenous, polar, ionizable cpd. Purpose: enhance excretion. Reaction types include: C C Glucuronidation ulfate formation Acetaminophen - ulfate + C - C Glucuronide 9

10 Phase-1 & Phase-2 Complimentary T Mutually Exclusive R Phase 1 R 2 2 Phase 2 Excretion - R 2 Principle ites of Drug Metabolism Liver Major xenobiotic metabolism nonessential exogenous (foreign) compounds Major endobiotic metabolism endogenous compounds The Presystemic "First pass effect" Principle ites of Drug Metabolism General ystemic Circulation Liver Portal Vein tomach Intestine 10

11 Presystemic First Pass Effect ource: epatic first pass metabolism. Metabolism by GI mucosa during absorption. ignificance? regular drugs prodrugs ee Foye s Table 8.13 ow vercome? Principle ites of Drug Metabolism GI Tract Epithelium very rich in drug-metabolizing enzymes; phase-1 and phase-2 (significant contribution oral bioavail) Gut flora Reduction (e.g. azulfidine) deconjugation (e.g. premarin) enterohepatic recycling (EC) Endobiotic = bile salt recycling Xenobiotic = conjugates >500 MW excreted by p- glycoprotein and MDR-2 transport systems into bile. Principle ites of Drug Metabolism Liver GI Tract Kidneys, Lungs, Brain, etc localized bioactivation (e.g. PA s in cigarette smoke) localized toxicity (e.g. MPTP) 11

12 Phase-1 vs. Phase-2 Metabolism Prof. Patrick Davis Basic Medicinal Chemical Principles PR 143M Fall-07 12