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Pharm > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

Concentration [C] =

A

Mass/Vol

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2
Q

Conventional PK measured in

A

Plasma

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3
Q

Serum =

A

Plasma minus coag factors

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4
Q

Total =

A

Protein bound and free drug

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5
Q

Usually Cb =

A

Cp

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6
Q

________ are concentrated in RBCs

A

High lipophilic drugs (cyclosporine/chloroquine)

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7
Q

Dose of drug administered –>

A

ADME

Absorption, Distribution, Metabolism, Elimination

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8
Q

Predictable relationship between…

A

plasma or serum concentration of drug and its effect

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9
Q

Three general goals of PK

A
  1. Establishing/adjusting dosage
  2. Dx of toxicoses
  3. Withdrawal times for food safety in babies
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10
Q

Distribution =

A

the dispersion of a drug through the fluids and tissues of the body

Vascular space/plasma –> extravascular space

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11
Q

Movement of drugs in the body…what are the three big locations?

A

Site of administration

Site of action

Site of excretion

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12
Q

AUC refers to what kind of plot?

A

Concentration-Time (C-T) ; During a single dose interval!

Describes the behavior (exposure) of the drug moving through the body

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13
Q

What are the two compartments we consider in absorption and distribution

A

Compartment 1 = Plasma/circulation

Compartment 2 = TIssue/system

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14
Q

Absorption is the process of a drug entering _________

A

the blood/systemic circulation

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15
Q

Bioability (F) =

A

The fraction of the drug entering into the circulating system

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16
Q

Oral absorption

A

Low absorption, low F

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17
Q

IV absorption

A

Instant, 100% absorption (F=1)

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18
Q

Intramuscular is __ than oral, with a…

A

Faster

Higher F

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19
Q

Subcutaneous vs IM absorption rate?

A

SubQ is slower

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20
Q

What two factors can influence the absorption of the drug?

A
  • Blood flow
  • Drug concentration at the site of administration
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21
Q

What is “F”?

Is there an equation to determine it?

A

Bioavailability

Equation:

Amount of drug absorbed into systemic circulation / Amount of drug administered

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22
Q

Oral bioavailability equation

A

F = (fraction % absorbed from gut lumen into the portal vein) * (Fraction excaping firstpass metabolism)

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23
Q

What is Eh?

A

Hepatic extraction ratio = fraction of drug extracted by the liver in first pass metabolism

Eh = (C1-C2) / C1

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24
Q

how to find (F) from comparing absorption routes?

A

F = AUC (PO) / AUC (IV)

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25
Q

Effect of Hepatic Extraction on Bioavailability

A

F = 1-Eh

(assuming 100% absorption into the portal vein from the gut)

26
Q

Alteration of the hepatic enzyme activity would most significantly alter a drug with a ______ Eh

A

High Eh

Most dose is eliminated by the liver, and the change in enzyme activity would change the bioavailibility to a greater percent of the original than if the BA were already very high.

i.e. You can’t accidentally double the BA of a drug when it’s already at 90+%

27
Q

Examples of drugs with high and low Eh

A

Low Eh = Throphylline

High Eh = Verapimil

28
Q

Formulations are considered bioequivalent when…

A

the extents and rates of absorption from them are so similar that there is likely to be no clinically important difference between their effects, either therapeutic or adverse

29
Q

Two products are considered bioequivalent if the….

A

90% CI of the AUC ratio is within the range of 0.8-1.25

30
Q

Equation for relative bioavilability

A

Fr = AUCgeneric/AUCbrand

0.8 < Fr < 1.25

31
Q

Factors that affect drug distribution (5)

A
  1. Size of organ
  2. Blood flow
  3. Solubility
  4. Binding (albumin, A1 acid glycoprotien, liproteins)
  5. Molecular Weight of drug
32
Q

Percent of total volume:

  • Intravascular volume
  • intracellular volume
  • interstitial volume
  • Adipose
A
  • Intravascular = 5
  • Intraceullular = 40
  • Interstitial = 15
  • Adipose = several percent
33
Q

Equation to find body volume

A

V = Mass/[C]

Assuming the drug is 100% absorbed into systemic circ., EVENLY distributed, and not excreted yet.

34
Q

What is Vd?

A

Apparent volume of distribution

= the theoretical volume that would be necessary to contain the total amount of an administered drug at the same concentration that it is observed in the blood plasma.

35
Q

Equation for apparent volume of distribution

A

Vd = Total amound of drug in body (A) / Plasma drug concentration (Cp)

36
Q

What might cause an inaccurate Vd?

A

Uneven distribution in body compartments

37
Q

Which example molecule had the highest/lowest Vd’s?

A

Highest = Imipramine

Lowest = IgG

38
Q

For a specific drug and a specific patient, Vd is ____

A

a constant

39
Q

Steady state =

A

Css

the condition in which the avg total amound of drug in the body remains stable over time of dosing

(rate of input equals rate of elimination)

40
Q

Maint. dose rate =

A

DR

rate (mass/time) of drug input to maintain the drug concentration at the steady state

41
Q

Loading dose is used to…

A

reach the Css more quickly

42
Q

Assuming a continuous I.V. administration,

A

It takes the same time for all doses to reach the steady state

43
Q

___ is important for calculating loading dose

A

Vd

Loading dose = Vd x Target plasma concentration

44
Q

Metabolism:

A

The irreversibletransformation of parent compounds into daughter compounds

45
Q

Most drugs are excreted by way of the

A

Kidney

46
Q

Definition of clearance

A

the efficiency that the drug volume is irreversibly eliminated from the volume of distribution

(The volume of plasma that has been cleared of a drug per unit time)

47
Q

Definition of Elimination rate

A

the amount of drug (mass) is irreversibly eliminated from the dose per unit time

How much (mass) of the drug eliminated per unit time

48
Q

Elimination rate constant definition

A

(K) the fraction of the drug volume is irreversibly eliminated from the volume of distribution per unnit time

PERCENT of drug eliminated per unit time

49
Q

Calculate Elimination Rate (ER)

A

ER = Clearance (CL) x Plasma concentration (Cp)

50
Q

Elimination rate constant equation

A

K = Clearance/ Volume of distribution

CL / Vd

51
Q

Increasing the drug plasma concentration will proportionately…

A

increase the elimination rate

52
Q

At steady state…

A

elimination rate = maintenance dose rate

53
Q

Equation for maintenance dose rate

A

Maintenance dose rate = clearance * Steady state []

DR = CL * Css

54
Q

When maintenance dose rate remains the same, changing the clearance will ______________ the Css

A

Proportionately and inversely change

55
Q

What is the only factor for calculating the maintenance dose rate?

A

Clearance

56
Q

How is the clearance affected? (what factors)

A

Induction/inhibition of the hepatic enzymes

Increased/decreased renal excretion

57
Q

When CL remains stable, what happens when we increase the DR?

A

The Css will be proportionately increased as well

58
Q

Measurement of total clearance (two ways)

A

CL = DR/Css

OR

CL = Dosemg/AUCmg*hr/L

(because DR = CL*Css)

59
Q

Organ extraction (Organ clearance) equation

A

Organ Clearance = Organ Extraction ratio (E) x Organ blood flow (Q)

CLH = Eh x QH

60
Q

For drugs extensively metabolized by the liver (high extraction ratio), EH is…

A

almost fixed, and will not effect clearance much. Therefore, clearance will be mostly based on organ blood flow (QH)

This is important for:

  • DDI when hepatic drug metabolism is reduced
  • Conditions that affect blood flow
61
Q

For drugs with high EH
increasing the hepatic metabolism will…

A

Reduce F

NOT change clearance

62
Q

For drug with low EH, increasing the hepatic metabolism will…

A

NOT change F

Increase the clearance

Pharm (4 decks)

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