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Pharm I > test 2 > Flashcards

test 2 Flashcards

1
Q

Distribution

A
  • After absorption, drugs must be distributed throughout the body
  • Accomplished through circulation via the bloodstream
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2
Q

Factors That Affect Distribution Dependent on

A
  • Blood flow (CO)
  • Capillary permeability
  • Protein binding
  • Lipophilicity
  • Tissue volume
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3
Q

Blood Flow affecting distribution

A

•Organs that receive higher flow receive higher drug concentrations
•High flow organs
-Heart, brain, kidneys, liver, skeletal muscles
•Low flow organs
- Adipose tissue
- Skin

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4
Q

Capillary Permeability affecting distribution

A

•Determined by capillary structure

-Varies in how much of the basement membrane is exposed by slit junctions between endothelial cells

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5
Q

Lipid solubility affecting distribution

A

•Move readily across most cell membranes
•Hydrophilic drugs do not penetrate the cell membrane
-Need slit junctions

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6
Q

Plasma Protein Binding affecting distribution

A

•Reversible binding of drug to plasma proteins

  • Sequesters drug
  • Nondiffusible form
  • Slows transfer out of the vascular compartment
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7
Q

when does protein binding occur

A

•Occurs when a portion of drug is bound to protein and is therefore not able to be free to bind to active sites and produce an effect

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8
Q

Albumin in the plasma

A
  • Major drug binding protein
  • Acts as a drug reservoir
  • Concentration of free drug decreases due to elimination, bound drug will dissociate from protein
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9
Q

less albumin leads to

A

-more free drug in the plasma that can cause an effect

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10
Q

Competing drug in the plasma

A
  • the competing drug takes up binding sites on the proteins allowing more free drug to cause more of an effect
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11
Q

Tissue Protein Binding affecting distribution

A

•Higher concentration of drug in tissues than in the extracellular fluid and blood
-Due to drug binding to lipids, proteins, and nucleic acids
-Due to active transportation of drug
•Drugs sequestered in the tissues
- Prolong drug action
- Cause local toxicity

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12
Q

what is Volume of Distribution (Vd)

A

•Fluid volume required to contain the entire drug in the body at the same concentration measured in the plasma

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13
Q

Volume of Distribution equation

A

Volume of Distribution = [amount of drug in the body] / [serum concentration]
OR
volume (L) = dose (mg) / [plasma drug] (mg/L)

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14
Q

what makes up the extracellular fluid

A
  • intravascular fluid

- interstitial fluid

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15
Q

what compartments do the drugs tend to be in

A
  • intracellular fluid
  • intravascular fluid
  • interstitial fluid
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16
Q

Plasma Compartment

A 
•4% of body weight
•High MW drugs
•Extensive protein bound drugs
•Drugs with a low Vd
are confined in plasma (intravascular fluid)
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17
Q

Extracellular Fluid Compartment

A

•20% of body weight
•Low MW drugs
•Hydrophilic drugs
-Confine in extracellular fluid (interstitial and plasma)
•Drugs confined to interstitial fluid have high Vd

18
Q

Volume of Distribution based on compartments

A
  • Drugs that are mostly confined to the intravascular space have a smaller volume of distribution
  • Drugs that have extensive distribution outside the plasma have a larger volume of distribution
19
Q

Calculating Vd:
500 mg of drug was added to a beaker with ? L of water. After mixing, measured drug concentration was 5mg/L.
What is the volume of distribution?

A

Vd = 500mg / 5 mg/L = 100 L

20
Q

Calculating Vd:
Patient weighing 70kg is given 1000mg of Drug A. Measured plasma concentration is 2mg/L.
What is the volume of distribution?

A

Vd (L)= 1000 mg / 2 mg/L = 500 L
500 L / 70 kg = 7.1 L/Kg
- a high Vd = low plasma concentration which means mainly extracellular
- you would need to put in 1000 mg of drug into a container that contains 500 L of water in order to get the measured concentration of 2 mg/L

21
Q

Calculating Vd:
Patient weighing 70kg is given 350mg of Drug B. Measured plasma concentration is 25mg/L.
What is the volume of distribution?

A

Vd = 350 mg / 25 mg/L = 14 L
14 L / 70 kg = 0.2 L/Kg OR 200 mL/Kg
- low Vd = high concentration in plasma which means mainly intravascular

22
Q

Affect of Vd on Drug Half-life

A

•High Vd increases drug half-life
•Drug bound to tissue (low plasma concentration) so not available to excretory organs
•Factors than increase Vd
increase half-life

23
Q

Half-life (t1/2)

A
  • Time it takes for the drug concentration to decrease by ½ (once administered)
  • Used to determine drug dosing frequency
  • Depends on how quickly a drug is eliminated from plasma
  • Determines length of drug effect
24
Q

•If a drug has a plasma concentration of 1000mg/L and the drug has a half-life of one hour. How much of the drug is present after:

  • One hour?
  • Two hours
  • Three hours
  • Four hours
A

1 hour: 500
2 hours: 250
3 hours: 125
4 hours: 62.5

25
Q

Three major routes of elimination

A
  • Hepatic metabolism
  • Biliary elimination
  • Urinary elimination
26
Q

Most drugs are eliminated according to

A
  • Firstorder kinetics
  • A constant fraction of drug is eliminated in a given unit of time
  • Drug half-life is used to measure drug clearance
27
Q

Clearance equation

A

CL = (0.639 x Vd) / t½

28
Q

Clearance Example:
A 100kg patient is taking Lisinopril which exhibits first order elimination kinetics with a half-life of 12 hours and its distribution appears to be limited to the intravascular space. What is the clearance rate for Lisinopril in this patient?

A

CL = (0.639 x (4% of 100)) / 12 hr = 0.213 L/1 hr

29
Q

First-order kinetics

A
  • increase the plasma concentration of the drug = increase in rate of elimination
  • rate of elimination is proportional to drug concentration
  • constant proportion being eliminated
  • dependent on initial drug concentration
  • half life is constant
  • 95% of the drug follow first order kinetics
30
Q

Zero-order kinetics

A
  • increase plasma concentration of the drug = no increase in rate of metabolism
  • rate of elimination becomes independent of concentration
  • a constant rate being eliminated
  • 5% of the drug follow zero-order kinetics
31
Q

A patient was given 100mg of Drug A orally. Assume that the drug metabolism follows first-order kinetics at a rate of 10% per minute

  1. dose given
  2. proportion being metabolized
  3. drug metabolized in the first min?
  4. 2nd
  5. 3rd
  6. 4th
A
  1. 100 mg
  2. 10%/min
  3. 10 mg
  4. 9 mg
  5. 8.1 mg
  6. 7.29 mg
32
Q

A patient was given 100mg of Drug B orally. Assume that the drug metabolism follows zero-order kinetics at a rate of 10mg/min

  1. How much drug is metabolized every minute?
  2. drug is metabolized after 5 minutes?
  3. 8 minutes
  4. How long will it take for all of the drug to be metabolized?
  5. How long will it take for 200mg of drug to be metabolized?
A
  1. 10 mg
  2. 50 mg
  3. 80 mg
  4. 10 minutes
  5. 20 minutes
33
Q

Drug Metabolism

A
  • Breaks drug down into metabolites
    • more water-soluble components
    • Aids in excretion of drug
  • Occurs by chemical reactions
    • Oxidation
    • Conjugation
    • Acetylation
    • Glucuronidation
  • Liver is the major organ for drug metabolism
34
Q

Liver Drug Metabolism

A 
•Contains a microsomal drug oxidation system called the cytochrome P-450 system (CYP-450)
- enzyme system
  •Induced
      •Increased activity
  •Inhibited
      •Decreased activity
35
Q

Phase I Biotransformations (breaks down the metabolites)

A
  • Converts lipophilic drugs into more water soluble molecules
    • Introducing or unmasking polar groups
    • OH or NH2
  • Chemical reactions involved:
    • Reduction
    • Oxidation
    • Hydrolysis
  • Metabolites often still too lipophilic
36
Q

Phase II Biotransformations (breaks down the metabolites)

A
  • Consists of conjugation reactions
    • Linking an acid (glucuronic, acetic, amino, sulfuric) to phase I metabolite
  • Resulting in a more water-soluble compound
    • Often therapeutically inactive
37
Q

Inducers of cytochrome P-450

A
  • Increase activity of CYP 450 enzymes
  • Increased biotransformation
  • Decreases plasma drug concentration and loss of therapeutic effect
38
Q

Inhibitors of cytochrome P-450

A
  • Decrease CYP 450 enzymes
  • Can lead to adverse side effects
  • Prolongs therapeutic drug effect
  • Decreases elimination
  • Lead to toxicity
39
Q

Drug Clearance by the Kidneys

A
  • Most important route of drug elimination
  • Renal elimination involves
    • Glomerular filtration
    • Tubular secretion
    • Tubular reabsorption
40
Q

Renal Elimination

A

Urine excretion = filtration + secretion - reabsorption

Pharm I (15 decks)

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