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ASC306 > L5: Pharmacokinetics II > Flashcards

L5: Pharmacokinetics II Flashcards

1
Q

What % is IV administration bioavailavable?

A

100%

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2
Q

What is meant by first pass metabolism?

A
  • pre-systemic elimination
  • drug is absorbed in GIT and goes into portal circulation and is metabolised by liver
  • Drug may no longer work
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3
Q

What is an exipient?

A

inactive substance used to carry an active substance (what drug is carried in)

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4
Q

Why would you use a hydrophilic dispersant (excipient), such as lactose?

A
  • Fast release as it is water soluble
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5
Q

Why would you use an inactive substance, such as talcum, as an excipient?

A
  • slow release (not water soluble)
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6
Q

Which is more important when considering drug absorption:
size of molecule or route of admin?

A
  • route of admin
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7
Q

Absorption of drugs by all routes is dependant on?

A
  • lipophilicity of drug (not an absolute though)
  • pH of drug and enviro
  • SA
  • 1st pass metabolism
  • vascularity and disease process
  • presence of ingesta
  • microbial metabolism (species dependent)
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8
Q

How are drugs absorbed?

A
  • Need to be lipophilic and hydrophilic, though more lipophilic
  • This is so they can pass through cell membranes and dissolve in our aqueous body fluids
  • Charged molecules leave circulation via phenustrates in capillaries => interstitial fluid => membrane => become uncharged => target organ
  • Non-polar lipophilic best at crossing membranes
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9
Q

Can strongly ionised compounds cross membranes?

A
  • helllll nawwww
  • The greater the difference b/w drug pH (pKa) and enviro pH, the more ionised the drug is
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10
Q

Drug distribution reflects?

A
  • ability of the drug to cross lipid membranes (lipophilicity)
  • the extent that the drug binds to tissue and fluid constituents
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11
Q

How do we calculate volume of distribution (Vd)?

A
  • Vd = Dose (mg/kg)/Co
  • Co is concentration at time zero
  • only time Co is accurately known is immediately after IV injection
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12
Q

How do we calculate a loading dose (LD)?

A
  • LD = Vd x target c (concentration steady state aka Css)
  • Target c is determined by dose-response curves
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13
Q

What is the pharmcokinetic definition of metabolism?

A
  • Essentially the conversion of a lipophilic compound to a more hydrophilic one in order to facilitate elimination
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14
Q

Describe phase I reactions (presynthetic)

A
  • Conjugation of a chemical group or molecule via hydroxylation, oxidation, reduction or hydrolysis
  • adding charge
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15
Q

Describe phase II reactions

A
  • Involves the conjugation of endogenous hydrophilic compound
  • no fucking idea what that actually means
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16
Q

What are the sites of drug metabolism for the different phases?

A
  • Phase I primarily hepatic
  • Phase II hepatic, renal and gut wall
  • For many drugs metabolism is proportional to hepatic blood flow
17
Q

What factors may affect drug metabolism?

A
  • species, breed
  • induction or inhibition of HME (hepatic microsomal enzymes)
  • hepatic function
  • age
  • diet
  • obesity
  • concurrent meds
18
Q

What are the major modes of elimination?

A
  • hepatic excretion -passed in faeces
  • renal excretion -passed in urine
  • miscellaneous -exhalation, sweat etc
19
Q

Will glomerular filtration remove those drugs or metabolites that are bound to proteins present in blood plasma?

A

No. Will only remove unbound drugs

20
Q

Only unbound drug is able to equilibrate across membranes

True or False?

A

True

21
Q

What is clearance?

A
  • the volume of blood (or plasma) from which a drugf would appear to be removed per unit time to account for its elimination
  • is the sum of all modes of metabolism/elimination
  • Usually expressed in units of mL/min/kg or L/hr/kg
  • affects half-life and accumulation
  • Cl = [urine] x rate of urine formation
    /
    [plasma]
22
Q

A drug candidate is very hydrophilic and does not bind to plasma proteins- is it likely to have a short or long half-life?

A
  • It will have a shorter half life
  • Lipophilic drugs may have an increased volume of distribution (Vd) with a prolonged half-life
  • Lipophilic = distributes through membranes with preference for adipose tissue and muscle (greater volume of distribution)
  • Hydrophilic = remains mostly in blood compartment until the drug is eliminated
  • An increase in the volume of distribution of a drug will generally increase its elimination half-life
  • A decrease in volume of distribution with an increase in elimination clearance will generally decrease elimination half-life
23
Q

Bioavailability is determined using? (parameter)

A
  • AUCt
  • “ratio of area under the curve”
24
Q
A

ASC306 (14 decks)

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