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BMR 605 > Test 1 Pharmacokinetics > Flashcards

Test 1 Pharmacokinetics Flashcards

1
Q

What is the basic principle of pharmacokinetics?

A
  • The effect of a drug is related to the blood concentration of the drug.
    • Therefore, changes in blood concentration will modify the effect of the drug.
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2
Q

Define and describe Bioavailability

A
  • Fraction of unchanged drug reaching the systemic circulation after administration.
  • Drugs administered by intravenous route have a bioavailability of 1, all other routes are < 1.
  • Bioavailabilty is denoted in most formulas by “F”.
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3
Q

How is bioavailabilty determined?

A
  • Comparing plasma concentration of drug over time between IV route and other routes.
  • The area under the curve (AUC) vs. time is an index of the extent of drug that enters the bloodstream and thus the body.
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4
Q

What is the bioavailability equation?

A

F = AUCoral
AUCiv

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5
Q

Define and describe Half-life?

A
  • Half-life is the time needed for a 50% decrease in plasma drug concentration
  • Denoted as t1/2
  • Expressed in units of time (usually hr)
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6
Q

What is the Half-Life formula in a one compartment model when the elimination rate constant (ke) is known.

A

t1/2 = (Ln 2)/ke = (0.693)/ke

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7
Q

What is the four half lives rule?

A
  • A drug is considered essentially eliminated from the body after 4 half-lives.
  • 94% of the drug is eliminated and only 6% remains in the body.
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8
Q

Define and describe Volume of distribution

A
  • The apparent volume that a drug would be distributed within the body once an equilibrium is established with palsma.
  • Denoted by Vd
  • Expressed in Liters or Liters/kg
  • Volume of distribution is an apparent volume.
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9
Q

Large volumes of distribution are an indication of a drug that is?

A

Highly lipophilic or has low protein binding.

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10
Q

What is the formula for Vd?

A

Vd = Dose(iv)
C0

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11
Q

How can Vd be graphically determined?

A

Using Plasma concentration at time 0.

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12
Q

Define and describe Clearance?

A
  • Clearance is the volume of plasma from which a drug is totally removed per unit of time.
  • Usually expressed as L/hr or mL/min
  • Drug can be removed by metabolism or excretion
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13
Q

Total Body clearance definition

A

Sum of all clearance values for a drug and are additive.

CL total = CLrenal + CLhepatic + CLother

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14
Q

What is the formula for clearance?

A

CL = Ke x Vd

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15
Q

Formula for clearance, when Ke = 0.693/t1/2

A

CL = 0.693/t1/2 x Vd

Rearranged for halflife:

t1/2 = (0.693 x Vd) / CL

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16
Q

The half life of a drug is dependent on what?

A

Clearance and Vd

17
Q

If clearance decreases and Vd stays the same what happens to half-life?

A

Half-life increases.

18
Q

Assuming a single drug administration, plasma concentration is ______ _________ to the dose administered. Provide the formula for this aswell.

A
  • Directly proportional
  • A = C x Vd
    • A = amt of drug
    • C = plasma concentration
    • Vd = volume of distribution
19
Q

Define and describe First Order Elimination Kinetics?

A
  • Definition: The rate of decrease in drug concentration is directly proportional to the amount of drug in the body.
  • A constant fraction of the drug is eliminated.
  • Elimination rate (Ke) is a constant.
20
Q

Most drugs follow what order kinetics?

A

First order Kinetics

21
Q

In First Order Kinetics the elimination rate (Ke) is a constant.

What does this mean?

A
  • Fraction of drug removed at any given time is constant and independent of dose.
    • ​Constant fraction eliminated.
22
Q

What does a graphic examination of first order kinetics look like.

A

The semi-log plot for one compartment first order kinetics will be a straight linear line.

23
Q

Define and describe One Compartment model including what its graphical model looks like.

A
  • A drug rapidly equilibrates between plasma and tissue relative to its elimination rate. The body acts as a single compartment.
  • Semi-log plot of plasma concentration over time is a straight line when the drug follows first order kinetics.
  • Changes in plasma concentration reflect a proportional change in tissue concentration.
    • ​The plasma and tissue concentrations may be different.
    • The drug does not inherently distribute to all tissues.
24
Q

Define and describe the Two compartment model:

A
  • A drug takes a longer time period to establish equilibrium between plasma and tissue
    • Drug has two compartments for distribution:
      • Central and a peripheral compartment.
        • Drugs can move between these two freely.
      • Elimination occurs from the central compartment.
25
Graphically describe the semi-log for two compartment model
* The semi-log plot results in two phases when the drug follows first order kinetics. * Initial distribution phase (more rapid decline in plasma drug concentration over time * Elimination phase (less severe continous decrease.
26
Describe **Zero Order Kinetics**
* Definition: **A constant amount of a drug is eliminated _independent_ of dose; the enzymes involved in elimination are saturated.**
27
Define and describe **Concentration at steady state (CSS)**
* **The plasma plasma concentration maintained at Steady state** * **​Attained after 4 half-lives.** * **CSS: rate of administration = rate of elimination**
28
Define and describe **Maintenance Dose:**
* Dose taken at regular intervals to keep concentration within a trough and peak. * **The fluctuations between the peak and trough are dependent on the dosing interval.** * **The _longer_ the dosing interval the greater the variation in peak and trough values.**
29
Mathematical formula for CSS?
* *CSS = _MD_** * *CL**
30
Mathematical formula for maintanence dose
``` **MD = _Dose x F_ Dosing interval(t)** ``` **t = dosing interval (its actually a greek t)**
31
Equation for **CSS for constant IV infusion**
* *CSS = _Infusion rate_** * *CL**
32
# Define and describe a **loading dose**? Equation?
A single large dose that can be given to produce an immediate rise in plasma drug concentration. ## Footnote **Loading Dose = _CSS x Vd_ F**
33
What is the Ke for a drug with a half-life of 3 hours?
Ke = _0.693_ = 0.231 h-1 3h

BMR 605 (10 decks)

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