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2a- Pharmacology > Principles of pharmacokinetics > Flashcards

Principles of pharmacokinetics Flashcards

1
Q

What is pharmacology?

A

The study of how medicines work and how they affect our bodies

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2
Q

What are the 2 branches of pharmacology?

A

Pharmacokinetics
Pharmacodynamics

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3
Q

What is pharmacokinetics?

A
  • The fate of a chemical substance administered to a living organism
  • What the body does to the drug
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4
Q

What is pharmacodynamics?

A
  • The biochemical, physiological and molecular effects of a drug on the body
  • What the drug does to the body
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5
Q

What is the process of pharmacokinetics?

A
  1. Absorption
  2. Distribution
  3. Metabolism
  4. Excretion
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6
Q

What is absorption?

A

Transfer of a drug molecule from site of administration to systemic circulation

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7
Q

What are different routes of administration?

A
  • IV (intravenous)
  • IA (intra-arterial)
  • IM (intramuscular)
  • SC (subcutaneous)
  • PO (oral)
  • SL (sublingual)
  • INH (inhaled)
  • PR (rectal)
  • PV (vaginal)
  • TOP (topical)
  • TD (transdermal)
  • IT (intrathecal)
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8
Q

Which methods of administration does 100% of it reach the systemic circulation?

A

IV or IA

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9
Q

Why does every route except IV and IA not have 100% of the dose reach systemic circulation?

A

For any other route, drugs must cross at least one membrane to reach systemic circulation

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10
Q

What are 4 mechanisms for drugs to permeate membranes?

A
  1. Passive diffusion through hydrophobic membrane
  2. Passive diffusion aqueous pores
  3. Carrier mediated transport
  4. Pinocytosis
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11
Q

Which type of molecules enter by passive diffusion through hydrophobic membranes?

A

Lipid soluble molecules

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12
Q

Which type of molecules enter by passive diffusion through aqueous pores?

A
  • Very small water soluble drugs (eg. lithium in drugs to treat BPD)
  • Most drug molecules are too big
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13
Q

Which type of molecules enter through carrier mediated transport?

A

Proteins which transport sugars, amino acids, neurotransmitters and trace metals (and some drugs)

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14
Q

What 2 factors affect drug absorption?

A
  1. Lipid solubility
  2. Drug ionisation
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15
Q

Are ionised drugs more or less absorbed?

A

Less

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16
Q

Are lipid soluble drugs more or less absorbed?

A

More

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17
Q

Why are ionised drugs less absorbed?

A
  • Most drugs are weak acids or weak bases with ionisable groups
  • Ionised drug has poor lipid solubility and therefore is poorly absorbed
  • Proportion of ionisation depends on pH of the aqueous environment
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18
Q

Why are so many drugs taken orally?

A

Convenient, cost effective

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19
Q

What factors of the stomach affect oral drug absorption?

A
  • Gastric enzymes - drug molecule may be digested (peptides, proteins)
    • Eg. insulin and biologicals not given orally
  • Low pH - molecule may be degraded (benzylpenicillin, has to be given as injection)
  • Food (full stomach will generally slow absorption)
  • Gastric motility (altered by drugs and disease state)
  • Previous surgery reduce absorption and transit time (eg gastrectomy)
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20
Q

What factors of the intestine affect oral drug absorption?

A
  • Drug structure:
    • Lipid soluble/unionised
      molecules diffuse down
      concentration gradient
    • Large or hydrophilic molecules
      are poorly absorbed
  • Medicine formulation:
    • Capsule/tablet coating can
      control time between
      administration and drug
      release
    • Modified release controls
      (slows) the rate of absorption
      (less frequent dosing)
  • P-glycoprotein:
    • Protective protein
    • Removes substrates from
      intestinal endothelial cells back
      into lumen
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21
Q

What is first pass metabolism?

A

Metabolism of drugs preventing them reaching systemic circulation

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22
Q

What are the 4 main barriers in first pass metabolism?

A

▪ Intestinal lumen
▪ Intestinal wall
▪ Liver
▪ Lungs

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23
Q

What is bioavailability?

A

proportion of administered dose which reaches the systemic circulation

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24
Q

What is bioavailability affected by?

A
  • Dependent on extent of drug absorption and extent of first pass metabolism
  • NOT affected by rate of absorption
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25
Q

What are pros of Rectal (PR) administration?

A
  • Local administration
  • Avoids first pass metabolism
  • Good when nausea and vomiting and oral isn’t possible
26
Q

What are cons of rectal (PR) administration?

A
  • Absorption can be variable
  • Patient preference
27
Q

What are features of inhaled (Inh) administration?

A
  • Large SA and blood flow but limited by risks of toxicity to alveoli and delivery of non-volatile drugs
  • Largely restricted to volatiles such as general anaesthetics and locally acting drugs such as bronchodilators in asthma
  • Asthma drugs non-volatile so given as aerosol or dry powder
28
Q

What are features of intramuscular (IM) administration?

A
  • Depends on blood flow and water solubility
    • Increase in either enhances
      removal of drug from injection
      site
  • Can make a depot injection by incorporating drug into lipophilic formulation which releases drug over days or weeks
29
Q

What are features of intradermal and subcutaneous (S/C) administration?

A
  • Avoids barrier of stratum corneum
  • Mainly limited by blood flow
  • Small volume can be given
  • Use for local effect or to deliberately limit rate of absorption
30
Q

What are pros of subcutaneous (S/C) administration?

A
  • Faster onset than PO
  • Formulation can be changed to
    control rate of absorption
31
Q

What is the con of subcutaneous (S/C) administration?

A

Not as rapid as IV

32
Q

What are the pros of transdermal (TD) administration?

A
  • Provides continuous drug release
  • Avoids first pass metabolism
33
Q

What are the cons of transdermal (TD) administration?

A
  • Only suitable for lipid soluble drugs
  • Slow onset of action
34
Q

When a drug first enters systemic circulation where is it?

A

In plasma

35
Q

What are the 4 compartments in the body?

A
  • Fat
  • Plasma
  • Interstitial fluid
  • Intracellular fluid
36
Q

What 3 properties of drugs influences their distribution?

A
  • Molecule size
  • Lipid solubility
  • Protein binding
37
Q

How does molecule size affect distribution?

A

smaller molecule more able to distribute

38
Q

How does lipid solubility affect distribution?

A

lipid soluble drugs able to permeate across membranes and distribute into tissues

38
Q

How does protein binding affect distribution?

A
  • greater affinity to proteins (albumin) so cannot permeate membranes and distribute
  • Binding lowers the free concentration of drug and can act as a depot releasing the bound drug when the plasma concentration drops through redistribution or elimination
  • Some drugs bind irreversibly and cannot re-enter the circulation and is equivalent to
    elimination
39
Q

Is binding to albumin for drugs reversible or irreversible?

A

Reversible

40
Q

What is volume of distribution (Vd)?

A
  • Theoretical volume a drug will be distributed in the body (apparent volume of distribution)
  • Volume of plasma required to contain the total administered dose
41
Q

Do drugs that are well distributed have a high or low Vd?

A

High

42
Q

What 3 ways can drugs reach the CNS through the BBB?

A
  • High lipid solubility. e.g. Ѱ drugs usually very lipid soluble (therefore large Vd)
  • Intrathecal administration (e.g. baclofen in MS and spinal cord injury, chemotherapy)
  • Inflammation (causes barrier to become leaky)
43
Q

What are adaptations of the BBB to protect the CNS?

A
  • Continuous layer of endothelial cells with tight junctions
  • Efflux pumps remove water soluble molecules
44
Q

What type of drugs can easily cross the placenta?

A

Lipid soluble drugs readily cross placenta

45
Q

What type of molecules can’t pass the placenta?

A

Large molecules do not cross placenta

46
Q

What is the method of elimination in foetuses?

A

Foetal liver has low levels of drug metabolizing enzymes, so relies on maternal elimination

47
Q

What is elimination?

A

the process by which the drug becomes no longer available to exert its effect on the body

48
Q

What are the 2 forms of elimination?

A
  • Excretion
  • Metabolism
49
Q

Which type of drugs are excreted?

A

unchanged drugs (hydrophillic, polar molecules)

50
Q

What is metabolism?

A

modification of chemical structure to form new chemical entity

51
Q

What are the steps in metabolism?

A

Phase 1
Phase 2

52
Q

What happens in phase 1?

A

Oxidation/reduction/hydrolysis to introduce reactive group to chemical structure

53
Q

What happens in phase 2?

A

Conjugation of endogenous functional group to produce hydrophilic, inert polar molecule involving formation of covalent bond

54
Q

What type of molecules is metabolism needed for?

A

Necessary for the elimination of lipid soluble drugs to then be excreted

55
Q

What enzyme is used in phase 1 reactions?

A

CYP450 enzyme

56
Q

How are drugs and metabolites excreted?

A
  • Liquids (small, polar molecules): URINE, bile, sweat, tears, breast milk
  • Solids (large molecules): faeces (through biliary excretion)
  • Gases (volatiles): expired air
57
Q

What are the 3 processes in renal excretion?

A
  1. Glomerular filtration
  2. Active tubular secretion
  3. Passive reabsorption
58
Q

What happens in glomerular filtration?

A
  • 20% of plasma filtered
  • Free/unbound drug molecules
  • Very large molecules excluded
59
Q

What happens in active tubular secretion?

A
  • 80% of renal blood flow passes on
    to peritubular capillaries
  • Drug molecules transported by carrier systems:
    • Organic anion transporter (OAT)
    • Organic cation transporter
      (OCT)
  • Can clear protein bound drug
  • Most effective renal clearance
    mechanism
60
Q

What happens in passive reabsorption?

A
  • Diffusion down the concentration gradient from tubule into peritubular capillaries
  • Hydrophobic drugs will diffuse easily
  • Highly polar drugs will be excreted

2a- Pharmacology (10 decks)

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