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PHRM 501 > Exam 3: Oral dosing > Flashcards

Exam 3: Oral dosing Flashcards

1
Q

The Importance of Pharmacokinetics

A

Drug concentration does not reach toxic levels
• Drug concentration is in the therapeutic range
• The duration of effect leads to practical dosing

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2
Q

Which modes of diffusion are saturable?

A

Facilitated diffusion

Active transport

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3
Q

Which modes of diffusion are unsaturable?

A

Passive diffusion

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4
Q

An orally administered drug must be absorbed

A

into the systemic circulation from the GI tract

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5
Q

How does an orally administered drug get absorbed

A

if in a solid form, it must first be released from its dosage form (tablet, capsule, etc.) – (liberation)
• Then dissolve in body fluids

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6
Q

There are physicochemical considerations to liberation and dissolution

A

pH
• Presence of food
• Dilution with liquids, etc

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7
Q

kinetic considerations to liberation and dissolution

A
  • Immediate/controlled release formulations
  • Gastric emptying time
  • Small intestine transit time
  • whether the drug is taken up by saturable or not saturable mechanisms
  • Blood flow, surface area, etc
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8
Q

At the peak, the rate of drug absorption equals

A

the rate of elimination

  • according to graph
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9
Q

In the graph, once plasma drug conc. declines, the rate of elimination becomes

A

greater than the rate of absorption

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10
Q

A drug is not absorbed until

A

it reaches systemic circulation

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11
Q

rate of elimination formula

A

Ke * [C]

where [C] is conc.

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12
Q

Rate of absorption formula

A

Ke * [C]

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13
Q

The absorption rate constant is important for

A

extravascular routes of administration

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14
Q

After administration, what happens to plasma conc.

A

the plasma concentration rises until it reaches a

peak

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15
Q

When the drug is being absorbed it is also

A

being eliminated simultaneously

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16
Q

Kinetics of oral dosing
When we first administer an oral
dose,

A

the rate of absorption is
greater than the rate of
elimination

ka[C]GI>ke[C]plasma

more drug in GI than Urine

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17
Q

Kinetics of oral dosing

Rate of drug entering = Rate of drug leaving

A

ka[C]GI=ke[C]plasma

Equal amount of drug in GI and urine

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18
Q

Kinetics of oral dosing
Then, as the drug in the
stomach/small intestine is
depleted,

A

the rate of elimination is
greater than the rate of
absorption
ka*[C]GI

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19
Q

A greater Ke means

A

faster elimination

shorter half life

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20
Q

A greater Ka means

A

faster absorption

most likely higher Cmax

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21
Q

If Drug A has a larger ke than Drug B, which drug will be eliminated first?
A. Drug A
B. Drug B

A

Drug A

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22
Q

As clearance decreases, conc. at steady state

A

increases

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23
Q

A drug with a high Ka will

A

reach it’s conc. much faster

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24
Q

What is tmax

A

the time required to reach max plasma drug conc.

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25
Q

tmax formula

A

tmax = ln (Ka) - ln (Ke) / Ka - Ke

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26
Q

Onset of effect /Latency

A
  • Time between dosing and start of therapeutic effect

• Time to reach the MEC

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27
Q

(AUC)

A

Area Under the Curve

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28
Q

AUC

A

Monitor concentration of plasma [drug] over time
• Time
• Drug concentration

is indicative of the body’s actual exposure to the drug

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29
Q

Greater AUC means

A

greater systemic exposure

  • greater therapeutic effect
  • also potential for toxicity
30
Q

Trapezoidal rule

A
  • method of finding AUC
  • Measure concentration at multiple time points
  • Area = ((C2+C1)/2)*(t2-t1)
31
Q

How is AUC done?

A 
- AUC is often done from t=0 to infinity
AUC0-inf
- AUC is sometimes done to the last measurable time
point
AUC0-t
- For steady state, AUC is usually done over the dosing
interval
AUC0-τ
32
Q

AUC formula

A

Dose administered / Cl

units are mg/ L/ hr

33
Q

Clearance formula

A

Ke * Vd

units are L/ hr

34
Q

If our clearance increases, our AUC will

A

decrease

35
Q

Larger clearace means

A

lower AUC

36
Q

Lower AUC means

A

less exposure to drug

37
Q

Lower clearance

A

high AUC, more exposure to drug

38
Q

A dosage form with slow absorption could yield plasma concentrations

A

to low to yield a therapeutic effect

39
Q

A dosage form with rapid absorption could

yield plasma concentrations

A

in the toxic range

40
Q

All of dose administered intravenously reaches

A

systemic circulation

41
Q

Bioavailability

A

amount of drug reaching systemic circulation versus the total amount of drug
administered

represented by F

42
Q

Bioavailability formula

A

amount of drug reaching circulation / dose administered

43
Q

Oral route of administration characteristics

A
  • Incomplete dissolution
  • Acidic pH
  • Destruction by digestive enzymes
  • Metabolism by intestinal enzymes
  • Biliary excretion to feces
  • Metabolism by the liver
44
Q

Other doses of administration may not reach systemic circulation bc:

A
  • Diffusion down concentration gradient
    • Limited by surface area
    • Limited by solubility
45
Q

Oral bioavailability is usually due to

A

to poor absorption or significant 1st pass

effect

46
Q

First pass metabolism

A

drug is metabolized before it reachers systemic circulation

47
Q

Routes when it comes to bioavailability

A

IV is 100 % by definition
Intramuscular and subcutaneous - 75-100%
Oral - 5-100% bc of 1st pass effect
Rectal 30-100%- less 1st pass effect than oral

48
Q

AUCiv

A

amount of drug in plasma if 100% had been
absorbed
Total amount of drug administered directly into the systemic
circulation
• Dose bypassing absorption (

49
Q

If a drug is administered by IV, which part of ADME is skipped

A

Absorption

50
Q

AUCroute

A

actual amount of drug that gets into plasma

• Mass after absorption

51
Q

Massafter absorption =

A

Mtotal mass administered * Froute

52
Q

Greater bioavailability(F) means

A
  • more potential for toxic effects

- most likely higher Cmax

53
Q

The AUC for IV is

A

dose/clearance

54
Q

The AUC for other routes of administration

A

has to take into account bioavailability

dose *F / Cl other

55
Q

Bioequivalence

A
  • A generic drug must have the same quality, strength, and safety as its brand name equivalent
  • Lack of significant difference in the rate and extent to which the active ingredient of a drug
    becomes available at the site of action when administered at the same dosage and under the
    same conditions
56
Q

In-vivo performance

A
  • PK studies

- Bioavailability

57
Q

In-vitro performance

A
  • Dissolution rate

- Drug release rate

58
Q

Cmax indicative of

A

rate of absorption
Peak exposure
• May vary depending on ka

59
Q

The peak concentration is known

A

as Cmax

60
Q

The trough concentration is known

A

as Cmin

61
Q

The dosing interval (τ)

A

is the time which we allow to elapse between doses

62
Q

For orally administered drugs, dosing intervals are typically every

A

6, 8, 12, or 24 hours

63
Q

The fewer number of times a drug has to be taken per day

A

the more likely the patient will be to stick with the

regimen

64
Q

Appropriate dosing intervals are dependent on the half-life of a drug and the therapeutic range

A

If your drug has a half-life of 8 hours, a patient’s symptoms may return if taken only once daily
• If your drug has a half-life of 24 hours, a patient may experience symptoms of toxicity if taken 3x daily

65
Q

IV administration, plasma drug concentrations will also reach a steady state

A

Css = (dose*F)/(Cl * τ)

66
Q

IV administration, plasma drug concentrations will be dependent

A

on the dose, bioavailability, clearance, and dosing interval

67
Q

Calculating Drug Accumulation

A

The concentration remaining after the 1st dose is additive with the concentration of the second dose

Cmax2 = Cmax1*(1+e-k τ
)

Cmax2= Cmin1 + Cmax1

68
Q

When a steady state concentration is reached

A

the equivalent of one dose is removed every dosing interval

69
Q

If dosing interval=half life

A

the plasma concentration of

drug fluctuates 2-fold over the dosing interval

70
Q

Rate of administration formula

A

Ra = dose / time

PHRM 501 (21 decks)

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