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VetMed Pharmacology4
VetMed Pharmacology - Metabolism
| Question | Answer |
|---|---|
| Importance of Pharm Metabolism | influences plasma drug concentrations facilitates improved excretion has a protective effect influence efficacy and side effects influenced by co-administration of multiple pharms influenced by disease |
| Goals of Pharm Metabolism | pharmaceutical inactivation enhanced pharm excretion convert "pro-drugs" to a biologically active form metabolized to a highly toxic metabolite(s) |
| Biotransformation Variables | species breed sex, repro status genetics stress and physiology diet age disease processes weight time of day hormonal/endocrine status absorption (PO vs. IV) induction of metabolism pathways by exogenous pharms or toxins inhibition of biochem |
| Objective of Phase I Metabolism | small chemical groups associated with a given pharm are biochemically transformed into a more polar form that increases their aqueous solubility |
| Effects of Phase I Metabolism | decreases pharm bio activity decreases volume of distribution enhances probability of being excreted creates chemical "handles" for Phase II |
| Types of Phase I Non-Synthetic Biotransformation Reactions | P450-dependent oxidation reactions P450 independent oxidation reactions Non-microsomal oxidation reactions Reduction reactions Hydrolysis reactions |
| Microsomal Mixed-Function Oxidases | the major enzyme systems responsible for pharm metabolization |
| P450 Independent Hydrolysis Reaction | common metabolic pathway for esters and amines |
| Phase II Metabolism | not required Phase I metabolite is synthetically conjugated to a relatively large MW moiety |
| Effects of Phase II Metabolism | increases MW which increases aqueous solubility increases polarity which increases aqueous solubility inactivates "parent" pharm |
| Results of Phase II Metabolism | decreased distribution of synthetic metabolites throughout body decreased passive diffusion across biliary tree decreased passive diffusion out of urinary filtrate |
| Glucuronidation | most common Phase II conjugation reaction |
| Glucuronyl Transferase | enzyme involved in glucuronidation deficient in cats, mammalian fetuses, early-age neonates |
| Anatomical Locations of Phase I Metabolism Reactions | liver (primary) kidney lung |
| "Pro-drug" Metabolism | pharm given is inactive and then metabolized to a biologically active form |
| Toxic Metabolite | the metabolite is more toxic than the parent pharm |
| Induction of Cytochrome P450 Enzyme | phenobarbital increases activity of cP450, thus increasing the rate of metabolism of the substrate (i.e. Warfarin) |
| Microsomal Mixed-Function Enzyme Systems | only class of enzyme systems that can be induced |
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