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PHA222 > ADME > Flashcards

ADME Flashcards

1
Q

What is a drug?

A

chemical substance that affects physiological function in the body

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2
Q

why are drugs administered?

A

to restore homeostasis - process maintaining a constant internal environment despite external changes

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3
Q

Define pharmacodynamics.

A

what the drug dose to the body

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4
Q

Define pharmacokinetics.

A

what the body does to the drug

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5
Q

What is bioavailiablity?

A

fraction of administered dose dose of intact drug that reaches systemic circulation

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6
Q

what does bioavailability depend one?

A

absorption

metabolism

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7
Q

What is absorption?

A

extent to which the intact drug is absorbed from the gut into circulation

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8
Q

Drugs cross through a bio-membrane via what?

A

Paracellular
- conective absorption

Transcellular

  • passive diffusion
  • facilitated diffusion
  • active transport
  • ion-pair absorption
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9
Q

Describe conective absorption

A
  • small molecules e.g. water urea

- sieving effect - if molecule is small enough, ti will pass through small pores

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10
Q

Describe passive diffusion

A
  • non-charged species

- down a concentration gradient

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11
Q

Describe facilitated diffusion

A
  • Spontaneous passage of molecules/ions e.g. Na+/glucose using ion channel/carrier proteins
  • small/charged molecules
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12
Q

Describe active transport

A
  • molecules transported AGAINST concentration gradient using ATP
  • structurally specific to carrier molecules
  • Na+/K+ ATPase - Na+ OUT , K+ IN
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13
Q

Describe ion pair absorption

A
  • ionised compounds form complexes with oppositely charges ions resulting in neutral species
  • move through membrane as a pair
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14
Q

State Lipinski’s rule

A
  • Log P <5
  • Mw <500amu
  • MAX 10 HBAS
  • MAX 5 HBDs

Polar drugs that break these rules are poorly absorbed

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15
Q

State Fick’s Law

A

Rate of diffusion is directly proportional to the membrane SA concentration gradient is inversely proportional to membrane thickness

  • If A (SA) increase
  • If C2/C1 increase = faster drug absorption
  • If P increase
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16
Q

What is pH partition hypothesis

A

If pH differs on either side of membrane, the drug will be ionised to different extents

17
Q

What does hydrophilicity mean?

A

drugs must be in solution to be absorbed

18
Q

what does lipophilicity mean?

A

drugs need to reach active site and cross membrane

19
Q

Define partition coefficient.

A

equilibrium between 2 phases depends on affinity for each

  • If P increase - drug highly lipophilic
  • influenced by - temp and solvent
20
Q

Describe the simple partition law

A

Ratio of conc between phases is not the same as predicted for unionised drug

  • ionised in aq layer
  • unionised in aq and org

Papp = Ptrue x fu

Papp = apparent P at pH
Ptrue - P of unionised drug

21
Q

What is the distribution equation?

A

Vd = Q/Cp

Q - total amount of drug in body
Cp - plasma drug conc
Vd - measure of a drug’s tendency to move from blood plasma to another site

22
Q

Equilibrium depends on what?

A

P
pH
permeability

23
Q

Describe Evan’s blue dye

A

high affinity for plasma albumin that enters intravascular space

  • Vd measures plasma volume
  • Assess permeability of BBB to macromolecules
  • When BBB compromised, albumin bound Evan’s blue enters CNS
24
Q

What does the amount of protein bound drugs depend on?

A

free drug conc
protein conc
drug affinity for binding site

25
Q

What are the effects of extensive plasma protein binding?

A
  • increase amount of drug absorbed

- increased competition for protein binding sites

26
Q

Describe drug metabolism.

A
  • aids elimination in liver and kidney
  • detoxification
  • metabolism introduces hydrophilic functionality - excretion in urine results in loss of pharmacological activity
  • increase therapeutic action
27
Q

When the If rate of metabolism decreases what happens?

A
  • increase intensity + duration of drug action

- increased amount of parent drug in plasma - increases toxicity

28
Q

When the If rate of metabolism increases when happens?

A
  • decrease intensity and duration

- increase toxicity due to production of toxic metabolites

29
Q

Describe Phase I drug metabolism

A

Introduces polar functional groups to molecules and provides site for Phase II

Oxidation (+ O atom)

  • oxidases located in liver
  • enzyme - CYP450
30
Q

Describe the enzyme CYP450

A

induction/inhibtion of metabolism of one drug by co-admin of another

31
Q

What does a CYP450 inducer do and give an example?

A
  • increase activity
  • rate of metabolism increase

example - carbamazepine

32
Q

What does a CYP450 inhibitor do and give an example?

A
  • decreases activity
  • rate of metabolism decreases

example - erythromycin

33
Q

Describe Phase II drug metabolism

A

Detoxification

Attach polar molecules to Phase I metabolites via transferases

increase hydrophilicity

  • increase H-bonding via -OH groups
  • conjugated excreted in bite liberating free drug

Via conjugated reaction

  • most common - glucuronic acid
  • sulphate
  • glycine
  • glucathione
  • methyl
  • acetyl

PHA222 (13 decks)

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