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Pharmacology > Principles Of Drug Therapy 4 > Flashcards

Principles Of Drug Therapy 4 Flashcards

1
Q

What are Ke and K?

A

Ke: measure of ability to elim
K: measure of the size of the hole

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2
Q

What is 1st order elimination?

A

The rate of ⬇️ in plasma drug conc is prop to the plasma drug conc

The rate of ⬇️ of height in bucket is prop to height of water column

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3
Q

How does the plasma drug conc change as func of time?

A

Exponentially, takes same amount of time for conc to drop to half its value

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4
Q

When does a 1st order process yield a straight line?

A

Log of drug vs time

ln[X]t = ln[X]0 - ke x t

Slope = ke, if log to base e is plotted

Ke x t1/2 = 0.69, a constant

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5
Q

What is elim 1/2 life?

A

How long after admin will drug fall to 50%.

4-5 half lives

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6
Q

Re: elim rate, what’s the prop constant?

A

Clearance, vol/min

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7
Q

What’s the relationship between k and CL?

A

Same as that of between amount of drug in body and plasma drug conc

Related via Vd

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8
Q

Relating CL and k and 1/2 life?

A

t1/2 = 0.69 x Vd/CL

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9
Q

What are t1/2 and k dependent on?

A

CL and Vd

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10
Q

What’s the leaky bucket model?

A

If heights and hole sizes are = then the rates of leakage from 2 buckets are =

But level falls slower in wider bucket (⬆️Vd)

So, t1/2 is longer and ke is smaller

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11
Q

What’s the RE (rate of elim) formula? Why’s it important?

A

RE = CLtotal x [X]blood

Helps us to determine dose to maintain desired [drug]blood

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12
Q

CLtotal?

A

= CLkidney + CLliver + CLother

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13
Q

Diff between 1st and 0 order?

A

1st: rate ⬇️ linearly with pressure/con
0: “” independent of “”

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14
Q

How might a drug be 1st order then 0 order?

A

Some drugs elim by biotransformation or active secretion

May use enz/pumps, so can become saturated (reach Rmax)

1st order at low dose, approach 0 at higher

Blood levels of drugs elim by 0 order kinetics are difficult to control

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15
Q

What order is abs and what does it lead to?

A

1st order

⬆️ plasma drug conc

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16
Q

Xblood formula?

A

[X]blood = Xadm/Vblood

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17
Q

What order is distribution and what does it lead to?

A

1st
⬇️ in plasma conc
Very evident for IV drugs or if abs is really fast

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18
Q

How does conc of drug in blood vary with time after admin OF A SINGLE DOSE?

A

Depends on rates of abs, elim and distribution

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19
Q

What are the kinetics of distr + elim?

A

Rapid admin of IV:

Xplasma = Xad/Vplasma

No elim:
Xplasma = Xad/Vdistr

After distr: conc falls b/c of elim

Semi log plot of elim is linear for 1st order

20
Q

What are the kinetics of abs and elim for IV and oral?

A

After IV:
conc ⬆️ fast then decline and elim

After oral:
Conc ⬆️ as abs happens, when abs ⬇️, elim ⬆️

Abs delays elim

21
Q

What is Cmax? Tmax? AUC?

A

Cmax = max plasma conc after single dose

Tmax = time to reach Cmax

AUC = dose(ad) x f/CL (exposure to drug)

22
Q

What’s determination of Vd(area)?

A

CL = 0.69Vd/t1/2

AUC can be used to calc Vd

23
Q

Bioavailability formula? CL? Vd (area)?

A

AUC(oral)/AUC(IV) = f

f=1 if abs is complete and clearance is same

CL = (dose x f)/AUC

Vd(area) = CL x t1/2/0.69

24
Q

The effects of dose on Cmax, AUC, Tmax, and DOA?

A

Cmax and AUC are prop to dose

Tmax and 1/2life are NOT PROP TO DOSE!!

DOA ⬆️ w/ dose, but NOT PROP TO DOSE!!

At certain dose the plasma come will fail to react MEC and DOA will be 0

25
Q

What’s the effect of ⬆️ CL for fixed dose w/ constant abs (ka)?

A

⬇️: AUC, half life, Cmax, Tmax

Term of action is sooner w/ little effect on onset

DOA⬇️

26
Q

What factors may affect CL?

A

Interactions: I- of secretion, changes in ENTEROHEPATIC cycling

Polymorphisms

Age/sex

Urine pH change affecting reab rates of weak a+bs

Disease

27
Q

Is DOA diff for oral v IV?

A

No

28
Q

When is the diff larger between plasma conc of IV and oral?

A

IV is much higher

Diff is larger when distribution is significant and slow

29
Q

What happens when you ⬇️ abs rate w/ fixed dose and constant clearance and t1/2?

A

Abs rates: 1, 1/2, 1/4, 1/8

AUC constant, Cmax ⬇️, Tmax ⬆️
DOA change is complex if MEC is 35
DOA values: 1.6, 1.74, 1.75 and 0

Cmax ⬇️ leads to DOA ⬇️ while TOA⬆️ leads to ⬆️DOA

30
Q

What are the effects of slowing abs?

A
  • ⬇️ avg blood conc
  • Will have small effect on DOA over certain range
  • if ka is slower than ke, elim will not reflect half life (since abs and elim phases overlap thru curve)
31
Q

What factors affect abs rate?

A

Site of admin
Formulation
Drug properties

32
Q

W/ slow release, if you ⬆️ the dose w/ 1/16th abs rate, w/ normal CL and 1/2life, what happens?

A

⬆️ plasma drug conc, DOA

33
Q

DOA of slow vs reg abs drug?

A

Slow release drug has ⬆️ DOA (5.4 v 1.6) AND onset

Same plasma conc

34
Q

Why do some drugs combine rapid and delayed release forms?

A

For fast onset and longer DOA

35
Q

What happens if a high dose formulation is abs rapidly? As in given via IV?

A

Longer DOA but plasma conc in toxic or lethal range

36
Q

What does the steady state drug conc (Css) depend on?

A

The fill rate and size of hole (CL)

37
Q

What’s infusion rate?

A

= CL x Css

For 1st order, CL is a constant

38
Q

When elim is saturated what’s the Css rise relationship to dose ⬆️?

A

It’s NOT PROP!

39
Q

The safe and effective dose range is wider for?

A

Drug elim by 1st order

40
Q

The time taken to reach steady state conc depends on?

A

Elim 1/2 life/clearance

Usually 5 half lives

41
Q

With mult dosing, plasma conc fluctuate and the choice of dosing interval depends on?

A

t1/2, MTC, MEC

narrower therapeutic range requires more frequent dosing of smaller doses

42
Q

For intermittent dosing, when do the fluctuations in [D]plasma ⬆️?

A

If the dosing interval ⬆️ (larger doses) and the rate of abs ⬆️ or Vd ⬇️

43
Q

What’s a loading dose? Formula?

A

Time taken to reach therapeutic range can be ⬇️ by giving a loading dose

**for peak Css max
LD = 2 x MD (maintenance dose)

**for mean Css max
LD = (Css mean) x Vd

44
Q

Why use loading doses? When might it be harmful?

A

For slow elim drugs to get into good range quickly

Harmful when rate of distribution is slow relative to abs

45
Q

What does t1/2 depend on?

A

CL and Vd

Pharmacology (7 decks)

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