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MT6314 (PCOL) > PHARMACOKINETICS > Flashcards

PHARMACOKINETICS Flashcards

1
Q

It is the effects of the biologic system on drugs

A

Pharmacokinetics

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2
Q

It deals with the processes of absorption, distribution and elimination of drugs

A

Pharmacokinetics

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3
Q

True or False

Pharmacokinetics makes possible the calculation of loading and maintenance doses

A

True

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4
Q

What are the 4 components of Pharmacokinetics?

A
  • Absorption
  • Metabolism
  • Distribution
  • Excretion
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5
Q

Acidic drugs bind to ______

A

Albumin

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6
Q

Basic drugs bind to ______

A

Alpha 1 Acid Glycoprotein

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7
Q

More highly protein bound drug will displace the ____ protein bound drug

A

Less protein bound drug

Drug A dislodges Drug B from inert binding site = higher efficacy of Drug B

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8
Q

What are the two basic parameters (known absorption)?

A
  • Volume of Distribution (Vd)
  • Clearance (CL)

  • It is unique for a particular drug in a particular patient
  • It is average values in large populations that can be used to predict concentration
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9
Q

What is the formula for Volume of Distribution?

A

Vd = amnt. of drug in the body / plasma drug conc.

Units: Liters or Vd/kg

  • plasma drug conc. or conc. of drug in the blood
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10
Q

It is the concentration of a drug at the receptor site (in contrast to drug concentrations that are more rapidly measured, eg, blood)

A

Effective Drug Concentration

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11
Q

What are the determining factors on Plasma Concentration

A
  • Rate of Input (absorption) into the plasma
  • Rate of distribution to peripheral tissue (includin target organ)
  • Rate of elimination, or loss, from the body
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12
Q

It is the measure of apparent space in the body available to contain the drug

A

Volume of Distribution (Vd)

- It is the amount of drug in the body to the plasma/serum concentration

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13
Q

When a drug is avidly bound in peripheral tissues, it’s concentration in plasma may drop to very low values even if the total amount in the body is large

A

High volume of distribution (Vd)

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14
Q

When a drug is completely retained in the plasma compartment

A

Volume of distribution is equal to the plasma volume

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15
Q

It is the rate of elimination compared to plasma concentration

It depends on the drug and the organs of elimination in the patient

A

Clearance (CL)

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16
Q

What is the formula for Clearance (CL)

A

Rate of elimination of drug / Plasma Drug Concentration (Cp)

units = volume/unit time

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17
Q

Drugs are eliminated with what order of kinetics

A

First-order kinetics

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18
Q

What is the formula for elimination rate

A

Elimination rate = clearance (constant) x plasma concentration

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19
Q

True or False

For most drugs, Clearance is constant over the concentration range

A

True

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20
Q

Rate of drug concentration is ____ proportional to the concentration

A

Directly proportional

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21
Q

Clearance depends on the following factors:

A
  • Drug (1st order or 0 order kinetics)
  • Blood flow
  • Condition of the organs of elimination (extraction capability of the organ and drug delivery to the organ)
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22
Q

True or False

Elimination will be rapid at first and slow as the concentration decreases

A

True

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23
Q

What order of elimination is this?

Clearance is constant over broad range of plasma concentration

A

First-order elimination

50% units/h is eliminated through time (e.g. 5 units/h, 2.5, 1.25)

  • faster
  • as the conc. increases = the rate of elimination increases (vice versa)
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24
Q

What order of elimination is this?

Elimination rate is constant on plasma concentration

A

Zero-order elimination

e.g. 2.5 units/h is eliminated through time

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25
It is the time it takes for the amount of concentration of a drug to fall to 50% of an earlier measurement
Half Life (t 1/2)
26
# True or False Half-life is dependent to the volume of distribution
True
27
Determines the rate at which blood concentration rises during a constant infusion and falls after administration is stopped
Half life (t 1/2)
27
# True or False Half life is a derived parameter from the volume of distribution and clearance
True
28
What is the formula of Half life?
t 1/2 = 0.693 x Vd / CL | Unit: time (hrs)
29
It is the average total amount of drug in the body which does not change over multiple dosing cycles
Steady State
30
The rate of drug administration is equal to rate of elimination
Steady State | Dose in = dose out
31
Fraction/percentage of the administered dose of the drug that reaches the systemic circulation
Bioavalability (F)
32
What is the formula for Bioavailability?
F = amnt of drug in the plasma / dose of drug administered
33
What is a common measure of the extent of F?
area under the blood conc.-time curve (AUC)
34
What is the bioavailability for Intravenous Administration (IV)?
F = 100% or unity
35
What are the effects when drug is administered through other routes?
- Reduced by incomplete absorption - 1st-pass metabolism - Distribution into other tissues before the target organ - Drug enters the systemic circulation
36
# True Drugs are more absorbed in the small intestines because it has a larger surface area
True
37
What are the factors affecting bioavailability?
- Extent of absorption - First-pass effect (measured as the extraction ratio and is avoided by sublingual, transdermal, & rectal supp.) - Rate of absoroption (site of administration and formulation of drug)
38
The following are to offset low bioavailability
- Sublingual - Rectal-50% probability of bypassing the 1st-pass effect - Inhalation or nasal - Transdermal patches
39
The AUC can be derived from?
- single-dose studies - multiple-dose measurements
40
What are the bioavailability of the following: - Intravenous - Subcutaneous - Intramuscular - Oral ingestion
- Intravenous: F = 1 (by definition) - Subcutaneous: 0.75 < F < 1 - Intramuscular: 0.75 < F < 1 - Oral Ingestion: .05 < F < 1
41
What is the absorption pattern of Intravenous route?
- Absorption circumvented - Potentially immediate effects - Suitable for large volumes and for irritating substances, or complex mixtures, when diluted
42
What is the absorption pattern of Subcutaneous route?
- Prompt from aqueous solution - Slow and sustained from repository preparations
43
What is the absorption pattern of Intramuscular route?
- Prompt from aqueous solution - Slow and sustained from repository preparations
44
What is the absorption pattern of Oral Ingestion route?
- Variable, depends on many factors
45
# Time Course of Drug Effects It is directly related to concentration e.g. anticoagulants
Immediate Effect
46
# Time Course of Drug Effects - This happens due to distributional delay - Delayed expression of the physiologic - substance needed for the effect
Delayed Effect
47
# Time Course of Drug Effects - Constant infusion - Aminoglycosides causes renal toxicity if given constantly - Intermittent dosing only
Cumulative Effects
48
Fraction or percentage of the drug removed from the perfusing blood during passage through the organ
Extraction ratio | Measure of the elimination of the drug by that organ
49
Drugs with **high hepatic extraction** ratio have a large ______
1st-pass effect
50
Desired therapeutic effects are produced in the _____
Target Concentration
51
Goal is to achieve therapeutic levels: maximal effect, least toxicities | Plan for drug administration over a period of time
Dosing Regimen
52
- Dose needed to maintain a steady state of concentration - It is to maintain plasma concentration over periods of time - Enough drugs to replace eliminated drugs
Maintenance Doses
53
Achievement of therapeutic levels of the drug in the body without exceeding the minimum toxic concentration
Dosing Regimen
54
- For drugs with long half-lives and longer time to reach a steady state - It is to achieve target plasma level rapidly/promptly | Volume of distribution (Vd) is important
Loading Dose
55
What is the most important parameter in defining rational drug dosage?
Clearance
56
# Maintenance Dosage What is the formula for Dosing Rate?
**CL** x desired plasma concentration / bioavailability
57
Doses per day is determined by?
- Half life - Therapeutic window | Maintain concentration higher than minimum therapeutic level at all time
58
What is the formula for Loading Dose?
**Vd** x desired plasma concentration / bioavailability ## Footnote If loading dose is large, the dose should be given slowly to prevent toxicity due to excessively high plasma levels during distribution phase
59
In ____ , drugs are eliminated unchanged or as metabolites | Polar compounds are more efficiently eliminated
Excretion
60
What is the most important organ in excretion?
Kidney | As well as Liver, GIT, Breast, Lungs
61
It is the safe "opening" or range between the: - Minimum therapeutic concentration - Minimum toxic concentration
Therapeutic Window
62
What determines the trough?
Minimum Therapeutic Concentration
63
What determines the peak?
Minimum Toxic Concentration
64
What are the variables of Pharmacokinetics?
- Absorption - Clearance - Volume of Distribution - Half Life
65
# What pharmacokinetic variable is this? - Compliance of patient is important - Variation in bioavailability are usually due to variation in metabolism during absorption
Absorption
66
# What pharmacokinetic variable is this? - Most important parameter in designing dosage regimen - Creatinine clearance: - CREATININE CLEARANCE: - Good indicator of renal function - Adjust the dosage of the drug - Not reliable indicator for liver function - Estimated GFR as surrogate for Creatinine Clearance tests
Clearance
67
# Volume of Distribution - decreased Vd: - increased Vd: - increased Vd:
- decreased Vd = binding to plasma proteins - increased Vd = binding to tissues * increased Vd = drug distributed to body waters, extracellular accumulation of body fluids
68
No more increase in effect even if the concentration is increasing
Maximum Effect (Emax)
69
- Reflected by EC50 – concentration required to produce 50% of maximum effect - Increased, exaggerated response to small doses
Sensitivity
70
When is the most appropriate time to measure drug concentration
- Absorption is complete - 2 hours after the dose
71
# True or False Under steady state concentration, condition in **3 to 4 t ½ must elapse** before checking drug blood concentration
True
72
Drugs given intermittently are in ______
steady state of concentration
73
It used to determine the range of plasma levels that is acceptable when designing a dosing regimen
Therapeutic Window
74
What is the absorption pattern of Oral Ingestion route?
- Variable, depends on many factors

MT6314 (PCOL) (6 decks)

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