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intro to clinical sciences phase 2 > principles of pharmacokinetics > Flashcards

principles of pharmacokinetics Flashcards

1
Q

define pharmacology

A

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

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2
Q

what is pharmacology split into

A
  • pharmacodynamics
  • pharmacokinetics
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3
Q

define pharmacodynamics

A

the biochemical, physiological and molecular effects of a drug on the body

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4
Q

define pharmacokinetics

A

the fate of a chemical substance administered to a living organism

the action of drugs in the body

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5
Q

whats the difference between pharmacodynamics and pharmacokinetics

A

pharmacodynamics is what the drug does to the body whereas pharmacokinetics is what the body does to the drug

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6
Q

define sub competency

A

the general skills and behaviours that are required to be able to complete a particular competency

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7
Q

what are the 4 sub-competencies of prescribing to ensure safe and effective decisions

A
  1. understand the actions of drugs (and medicines) on the body
  2. make prescribing decisions appropriate for individual patients
  3. undertake appropriate monitoring - for efficacy and adverse reactions
  4. avoid/anticipate drug interactions
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8
Q

what are the 4 processes of pharmacokinetics

A

absorption

distribution

metabolism

excretion

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9
Q

define absorption

A

the process of transfer from the site of administration into the general or systemic circulation

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10
Q

give all the routes of drug administration

A
  • oral
  • intravenous
  • intra - arterial
  • intramuscular
  • subcutaneous
  • inhalational
  • tropical
  • sublingual
  • rectal
  • intrathecal
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11
Q

whats different about IV and IA administration

A

100% of the dose reaches systemic circulation without crossing any membranes whereas for any other route the drugs most cross at least one membrane to reach systemic circulation

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12
Q

what are the 4 mechanisms for drugs to pass across membranes

A
  1. passive diffusion through the lipid layer
  2. diffusion through pores or ion channels
  3. carrier-mediated processes
  4. pinocytosis
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13
Q

which drugs use passive diffusion

A

lipid-soluble drugs

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14
Q

which drugs use diffusion through ion channels

A

small molecules, water-soluble drugs

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15
Q

which drugs use facilitated diffusion using carrier proteins

A

nutrients eg glucose and some amine neurotransmitters

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16
Q

which drugs use active transports

A

lots of them

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17
Q

which 2 factors affect drug absoprtion

A
  1. lipid solubility
  2. drug ionisation
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18
Q

define ionisation

A

a basic property of most drugs that are either weak acids or weak bases

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19
Q

why are ionisable groups essential for drug action

A

as ionic forces are part of the ligand-receptor interaction

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20
Q

which form of drugs are regarded as more water soluble

A

ionised = because has poor lipid solubility and therefore is poorly absorbed

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21
Q

which form of drugs are regarded as more lipid soluble

A

un ionised

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22
Q

what does the proportion of ionisation depend on

A

the ph of the aqueous environment

23
Q

what gives rapid and complete absorption of oral drugs

A

large SA and high blood flow of small intestine

24
Q

give 4 obstacles a drug needs to overcome to reach systemic circulation

A

drug structure

drug formulation

gastric emptying

first pass metabolism

25
Q

why is drug structure an obstacle

A

drugs need to be lipid soluble to be absorbed from the gut

;ipid soluble molecules diffuse down conc gradient

some drugs are unstable at low pH or in the presence of digestive enzymes so have to be given by alternative route

large or hydrophilic molecules are poorly absorbed

26
Q

why is drug formulation an obstacle

A

the capsule/tablet must disintegrate and dissolve to be absorbed

some are formulated to dissolve slowly or have a coating that is resistant to the acidity of the stomach

27
Q

why is gastric emptying an obstacle

A

the rate of gastric emptying determines how soon a drug taken orally is delivered to small intestine

can be slowed down via food and drugs or sped up via gastric surgery

28
Q

why is first pass metabolsim an obstacle

A

drugs taken orally have to pass 4 major metabolic barriers to reach circulation
1. intestinal lumen
2. intestinal wall
3. liver
4. lungs

29
Q

give 5 factors that affect oral drug absoprtion in the stomach

A
  1. gastric enzymes - drug molecule may be digested (peptides, proteins)
  2. low pH - molecule may be degraded
  3. food - full stomach will slow it down
  4. gastric motility - altered by drugs and disease state
  5. previous surgery - eg gastrectomy
30
Q

give 3 factors that affect oral drug absorption in the intestine

A
  1. drug struture
  2. medicine formulation
  3. P - glycoprotein
31
Q

give 3 types of absoprtion

A

intradermal and subcutaenous absoprtion

intramuscular absoprtion

inhalational absoprtion

32
Q

what does P glycoprotein do

A

substrates are removed from intestinal endothelial cells back into lumen

33
Q

describe Intradermal and subcutaneous absorption

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
34
Q

describe intramuscular absoprtion

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
35
Q

describe inhalational absorption

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 anesthetics and locally acting drugs such as bronchodilators in asthma
  • Asthma drugs non-volatile so given as aerosol or dry powder
36
Q

describe protein binding

A
  • Many drugs can bind to plasma or tissue proteins
  • may be reversible or irreversible
    -The most common reversible binding occurs with the plasma protein albumin
  • 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
37
Q

describe drug distribution

A
  • Lipid soluble drugs easily pass from blood to brain
  • The brain does little metabolizing and drugs are removed by diffusion into plasma, active transport in the choroid plexus or elimination in the CSF
  • Lipid soluble drugs readily cross placenta
  • Large molecules do not cross placenta
  • Foetal liver has low levels of drug metabolizing enzymes, so relies on maternal elimination
38
Q

describe elimination

A
  • The removal of a drugs activity from the body
  • May involve metabolism – the transformation of the drug molecule into a different molecule
  • Or excretion – the molecule is expelled in liquid, solid or gaseous waste
39
Q

describe metabolism

A
  • Necessary for the elimination of lipid soluble drugs
  • They are converted to water soluble products that are readily removed in the urine (if they remained lipid soluble they would be reabsorbed)
  • Metabolism produces one or more new compounds which may show differences from the patent drug
  • Drug metabolism may be divided into two phases
40
Q

what are phase 1 metabolism reactions

A

these reactions involve the transformation of the drug to a more polar metabolite

  • done by unmasking or adding a functional group
  • oxidations are the commonest reactions catalyzed by CP450
41
Q

what are phase 2 metabolism reactions

A

involves the formation of a covalent bond between the drug or its phase 1 metabolite and an endogenous substrate

  • Resulting products are usually less active and readily excreted by the kidneys
42
Q

what 3 things can drugs and metabolites be excreted in

A

fluids
solids
gases

43
Q

whats excreted in fluids

A

important for low molecular weight polar compounds (urine, bile, sweat, tears, breast milk)

Urine excretion: Total excretion = glomerular filtration + tubular secretion – reabsorption

44
Q

whats excreted in solids

A

faecal elimination

45
Q

whats excreted in gases

A

expired air important for volatiles

46
Q

what is the blood brain barrier

A

a membrane that seperated foreign substances in the blood from the CNS

it is a continuous layer of endothelial cells with tight junctions

efflux pump removes water soluble molecules

47
Q

role of BBB

A

maintains a stable environment and protects the brain but poses a challenge for treating CNS conditions

48
Q

give 3 ways for drugs to reach the CNS

A
  1. high lipid solubility
  2. intrathecal administration
  3. inflammation - causes barrier to become leaky
49
Q

what are the 4 compartments in the body

A

fat
plasma
interstital fluid
intracellular fluid

50
Q

which drug properties will influence ability to move between compartments

A

molecule size
lipid solubility
protein binding

51
Q

define volume of distribution

A

the theoretical volume a drug will be distributed in the body

it is the volume of plasma required to contain the administered dose

52
Q

which drugs will have a high Vd

A

drugs that are well distrbuted

53
Q

which drugs will have a low Vd

A

drugs that are poorly distributed

intro to clinical sciences phase 2 (48 decks)

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