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Flashcards

Pharmacokinetics & Pharmacodynamics 5

Florence Edwards Animal Disease 1 English 43 cards

Cards in this deck (43)

  1. 1What is an alternative term for metabolism?Biotransformation
  2. 2Where does drug metabolism occur?Primarily in the liver
    For some drugs metabolism can also occur in the plasma and intestines
  3. 3What are the 4 types of drug metabolite that can be formed?Inactive metabolites
    Active metabolites
    Toxic metabolites
    Pro-drug converted into active drug
  4. 4What are pro-drugs used for?Enhance bioavailability
  5. 5Give the 3 steps in hepatic drug metabolismDrug
    Converted to derivative in phase I
    Converted to conjugate in phase II
  6. 6What is the function of hepatic metabolism?Produce polar molecules which are not passively reabsorbed so the metabolite is more likely to be excreted by the kidney
  7. 7What is a phase I reaction in hepatic drug metabolism?Drug derivative formed by oxidation, reduction or hydrolysis
    Often introduce a reactive site into the drug molecule so it is more likely to undergo phase II
  8. 8What is a phase II reaction in drug metabolism?Conjugation of species formed in phase I with polar molecules
    This makes the metabolite water soluble (non-lipid soluble) so it is not passively reabsorbed
  9. 9Give 3 types of reaction that can occur in phase IOxidation
    Reduction
    Hydrolysis
  10. 10What type of reaction occurs in phase II?Conjugation
  11. 11Do all drugs undergo phase I reactions during their metabolism?No, some drugs undergo phase II reactions only
  12. 12What is an oxidation reaction?Addition of molecular oxygen
  13. 13What is the function of the drug phenytoin?Used to treat epilepsy
  14. 14Where are drug metabolising enzymes found in the liver?Endoplasmic reticulum
  15. 15What is the name for drug metabolising enzymes found in the liver?Microsomal enzymes
  16. 16Why is cytochrome P450 important in hepatic metabolism?Example of a mixed function oxidase enzyme
    Important for the oxidation reactions that occur during phase I hepatic drug metabolism
  17. 17Are drugs always metabolised by the same P450 enzymes?No - different cytochrome P450 enzymes have different specificities
    These are called cytochrome P450 enzyme isoforms
  18. 18Give an example of an important phase II reactionGlucuronide conjugation
  19. 19What is the phase I reaction in aspirin metabolism?Hydrolysis
  20. 20What is the phase II reaction in aspirin metabolism?Glucuronide conjugation
  21. 21What are the 5 factors that affect drug metabolism?Enzyme induction
    Enzyme inhibition
    Genetic polymorphisms
    Disease
    Age
  22. 22How does enzyme induction occur?Some drugs or environmental pollutants induce increased synthesis of cytochrome P450 over a number of days
  23. 23How can enzyme induction affect drug metabolism?Failure of drugs to produce therapeutic effect
    This is because clearance rate increases so half-life decreases, meaning an insufficient plasma concentration of the drug is reached
  24. 24Give the equation to calculate half-lifet0.5 = (0.693 x volume of distribution)/ clearance
  25. 25Describe how a Cp versus time graph for an IV drug bolus changes with enzyme inductionIncreased clearance means the concentration decreases more rapidly and the concentration of drug reaches zero after a shorter time period
  26. 26Describe how a Cp versus time graph for an IV drug infusion changes with enzyme inductionLower Css reached
    Also a lower half life so the Css is reached faster
  27. 27Give 2 examples of drugs that inhibit cytochrome P450 enzymesKetoconazole (anti-fungal)
    Cimetidine (treatment of stomach ulcers)
  28. 28How does enzyme inhibition affect drug metabolism?Drugs which inhibit cytochrome P450 may prolong the effects of other drugs metabolised by cytochrome P450
  29. 29Describe how a Cp versus time graph for an IV drug bolus changes with enzyme inhibitionConcentration decreases more slowly and takes longer to reach zero
  30. 30Describe how a Cp versus time graph for an IV drug infusion changes with enzyme inhibitionIncreased Css
    Longer half-life hence longer time to reach Css
  31. 31How do genetic polymorphisms affect drug metabolism?Poor ability to metabolise drugs by a proportion of the population due to genetic mutations which inhibit the action of certain enzymes
  32. 32How can cardiac disease inhibit hepatic metabolism?Inhibit metabolism of drugs which are rapidly metabolised by the liver, meaning their clearance is limited by blood flow
  33. 33How does an overactive thyroid affect hepatic metabolism?Induction of liver enzymes = enhanced metabolism
    Opposite occurs in hypothyroidism
  34. 34Give 3 examples of drugs that are excreted UNCHANGED via the kidneyPenicillin
    Digoxin (treatment for heart failure)
    Antenolol (beta blocker for treatment of high blood pressure)
  35. 35How does age affect drug metabolism?Liver capacity for drug metabolism lower in newborn and elderly animals, so these animals may require a lower
  36. 36Why is paracetamol toxic to cats?Limited glucoronidase enzyme so quickly becomes saturated
    Converted by P450 to toxic intermediate
    This can be conjugated with glutathione but this becomes depleted
    Reacts with cell macromolecules such as proteins causing cell death
  37. 37How is paracetamol normally metabolised?Phase II reactions only
    However, oxidation to toxic intermediate is a phase I reaction
  38. 38Why is N-acetyl-cysteine used to treat paracetamol toxicity?Replenishes glutathione which can react with and remove toxic intermediate
  39. 39What are pharmacodynamic drug interactions?2 drugs interact due to the effect they have on the body
    For example, aspirin and warfarin are anti-coagulants so synergise to cause haemorrhage
  40. 40What are the 4 types of pharmcokinetic drug interaction?Absorption
    Distribution/displacement
    Metabolism
    Excretion
  41. 41Give an example of a drug interaction that affects absorptionTetracycline and Ca2+/Mg2+ ions
    Ions coagulate with tetracycline and prevent its absorption
  42. 42Give an example of a drug interaction that affects metabolismEnzyme induction/inhibition
  43. 43Give an example of a drug interaction that affects excretionMethotrexate is a drug used to treat cancer
    NSAIDs inhibit excretion = toxic effects

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Animal Disease 1 (Pharmacokinetics & Pharmacodynamics) Flashcards on Pharmacokinetics & Pharmacodynamics 5, created by Florence Edwards on 23/10/2016.
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