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Pharmacology > Pharmacokinetics & pharmacodynamics > Flashcards

Pharmacokinetics & pharmacodynamics Flashcards

1
Q

What is the definition of pharmacokinetics?

A

study of how drugs move into, through, and out of the body

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2
Q

What is the definition of pharmacodynamics?

A

study of how drugs produce their effects in the body

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3
Q

What is therapeutic range?

A
  • ideal range of drug concentration within the body
  • we need to maintain the correct drug levels over the entire time the animal is being treated with the drug
  • too much can be toxic, too little has no beneficial effects and can result in ABX resistance
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4
Q

What is maximum effective concentration?

A

top end of the normal therapeutic range

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5
Q

What is minimum effective concentration?

A

bottom end of the normal therapeutic range - subtherapeutic if below

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6
Q

What factors influence blood concentration level or a drug and patients response to it?

A
  • rate of absorption
  • amount absorbed
  • distribution throughout body
  • drug metabolism or biotransformation
  • rate and route of excretion
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7
Q

What are the 3 components of therapeutic administration of drugs?

A
  1. drug dose
  2. dose interval
  3. route of administration

altering any one of these will result in drug concentrations being too high or too low

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8
Q

What is the purpose of a loading dose?

A

to raise the drug concentration to the therapeutic range very quickly

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9
Q

What are the 4 steps of pharmacokinetics?

A
  1. Absorption
  2. Distribution
  3. Metabolism
  4. Excretion
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10
Q

What is drug absorption?

A

Movement of drug molecules form the site of administration to the systemic circulation

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11
Q

What factors affect absorption?

A
  1. Route of administration (IV fastest)
  2. Bioavailability (degree to which a drug is absorbed and enters general circulation)
  3. Drug properties (lipophilic vs hydrophilic)
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12
Q

How do lipophilic drug molecules move?

A

quickly into cell membranes - absorb more slowly
Oral drugs must be lipophilic

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13
Q

How do hydrophilic drug molecules move?

A

quickly in extracellular fluid- absorbed more rapidly when given SQ or IM because when injected IM or SQ it has to move through ECF to reach blood vessels to be absorbed

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14
Q

How does tissue perfusion affect IM/SQ absorption?

A

amount of blood determines rate and degree of absorption, well used muscles, vasodilation & vasoconstriction

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15
Q

What other factors can affect oral absorption?

A
  • form of the drug (liquid vs solid)
  • motility of intestines (hypomotile = greater absorption, hypermotile = less absorption)
  • pH differences (stomach vs SI)
  • microbes
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16
Q

What is the first pass effect?

A

When the liver removes most or all of the drug in the “first pass” through it - the drug will not reach circulation for distribution

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17
Q

What are xenobiotics?

A

drugs that the liver recognizes as foreign substances

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18
Q

What is drug distribution?

A

movement of the drug from the blood into tissues - capillaries deliver the blood to the tissues from the blood stream

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19
Q

What factors can affect drug distribution?

A
  1. plasma protein binding (normal proteins that are present in the blood can bind to drugs - too large to exit bloodstream and keep the drug “protein bound” w/i blood vessels)
  2. Perfusion of tissues (reach highly vascular tissues more easily)
  3. Barriers (blood brain barrier - drugs must be small and lipophilic to enter brain)
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20
Q

What are P-glycoprotein pumps?

A

present in the brain - help pump out any drugs that do enter - also in testis and GIT (collies have low levels = more sensitive)

21
Q

What is drug metabolism?

A

drugs must be metabolized before they can be eliminated - called biotransformation and the altered drug molecule is called a metabolite

majority of enzymes involved in biotransformation are found in the liver

22
Q

What are prodrugs?

A

drugs that require biotransformation to become active (prednisone > prednisolone)

23
Q

What factors can affect metabolism?

A
  1. giving multiple drugs together (competition for enzymes = slower metabolic rate)
  2. species differences (cats have deficiency of glucuronyl transferase)
  3. age differences (young & old = decreased ability to metabolize)
  4. nutritional/health status (malnourished = less proteins to produce enzymes, liver disease)
24
Q

What is drug excretion?

A

movement of drug molecules out of the body - from the moment it enters the body, the body is trying to eliminate it

25
Q

What are the routes of elimination?

A
  1. kidney > urine
  2. liver > bile > feces
  3. milk/sweat
  4. lungs > inhalant anesthetics
26
Q

What is the most significant route of drug elimination?

A

through the kidneys via glomerular filtration

27
Q

What factors affect drug elimination?

A
  1. decreased blood flow to kidneys = decreased renal perfusion (hypotension - decreases blood flow into glomerulus = slower elimination, CHF - decreased blood flow to kidneys)
  2. increased blood flow to kidneys = increase renal perfusion (IVFT, drugs that increase perfusion = increased rate of elimination)
  3. kidney or liver compromise (decreased rate of elimination, hypoalbuminemia (low protein) = faster uptake of drug)
28
Q

How does biliary excretion work?

A

liver filters blood from systemic circulation as well as hepatic portal system - drugs excreted by liver move into bile and into duodenum

29
Q

What is half life (T1/2) of elimination?

A

the rate at which drugs leave the body is expressed as the drugs clearance, or half life of elimination

T 1/2 = the time it takes for the drug concentration in the blood to decrease by 50%

Lipophilic drugs typically have longer half lives

30
Q

What does a drugs half life determine?

A

dosage interval to maintain therapeutic concentrations

31
Q

What can affect a drugs half life?

A

liver and kidney function/impairment - results in longer T 1/2

32
Q

What is a steady state?

A

the point at which drug accumulation and elimination are balanced - correct interval and administration in healthy animals should allow the blood levels to stay steady in the therapeutic range

33
Q

What determines how quickly a drug reaches a steady state?

A

drugs elimination rate - the time from the beginning of therapy to the time the steady rate is reached equals 5 times the half life

34
Q

What types of drugs would we give a loading dose of?

A

Those that have a long half life because they take a long time to reach a steady state

35
Q

How are WT and T 1/2 related?

A

WT is based on half life of a drug, WT takes 10-11 half lives

36
Q

What is therapeutic index?

A

measure of how safe a drug is - need to know the dosage that will produce toxicity

37
Q

How do we calculate therapeutic index?

A

LD 50 = lethal dose in 50% of animals tx
ED 50 = effective dose in 50% of animals tx

TI= LD50/ED50

38
Q

What is the minimum TI to be licensed as a vet drug?

A

4

39
Q

What is the latent period?

A

the delay between administration of a drug and when the effects of the drug are seen

40
Q

What is efficacy?

A

represents the degree to which a drug produces its desired response, once efficacy is reached increasing the dose does not improve effect

41
Q

What are receptors?

A

components of a cell membrane that drug molecules combine with and alter the cell function (depression, stimulation, irritation, or death)

42
Q

What is affinity?

A

tendency of a drug to combine with a receptor

43
Q

What is an agonist?

A

drug with high level of affinity and efficacy - causes a specific action

44
Q

What is a partial agonist?

A

Drug with less affinity and efficacy

45
Q

What is an antagonist?

A

drug that blocks another drug from combining with a receptor

46
Q

What is an idiosyncratic drug reaction?

A

a reaction that is unusual or unsuspected

47
Q

What are some common adverse drug reactions?

A
  1. hypersensitivities - allergic reaction (anaphylaxis, swelling/hives, pruritis)
  2. Carcinogens (damage to DNA of a cell)
  3. Teratogens (cause birth defects if administered to pregnant animals - no real placental barrier)
  4. Organ toxicity (acute damage to heart or liver, chronic (copper in sheep - liver))
  5. CNS - blood brain barrier fairly effective (toxicity an issue with anesthetics or poisons
  6. blood cells and bone marrow (acetominophen, estrogen)
48
Q

What is TDM?

A

Therapeutic drug monitoring - periodically measure blood levels for certain drugs

49
Q

What are the 3 types of drug interactions?

A
  1. chemical/physical - may precipitate when mixed together
  2. pharmacokinetic - altered absorption, altered metabolism and elimination
  3. pharmacodynamic - interaction at site of drug action (agonist & antagonist)

Pharmacology (9 decks)

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