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Pharmacokinetics > Exam 1 Oral Dosing > Flashcards

Exam 1 Oral Dosing Flashcards

1
Q

What are the different routes of administration?

A
  1. IV bolus
  2. IV infusion
  3. extravascular
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2
Q

For an IV bolus dose, what is Cmax?

A

Cmax is t = 0

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3
Q

For an IV infusion, what is the Cmax?

A

the start of elimination → the maximum concentration of a given dose

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4
Q

The larger the AUC, the what?

A

the more exposure the patient has

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5
Q

What is tpeak of an IV infusion?

A

the time of Cmax (the max concentration of the given dose)

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6
Q

What are common extravascular routes?

A

oral, nasal, rectal, IM, SC, topical, aerosol bronchodilators, sublingual

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7
Q

What is unique about the extravascular concentration v time graph?

A

a time = 0, there is no drug in the body (starts out at 0 then rapidly increases, then reaches the Cmax, and then curves back down)

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8
Q

What is the most common extravascular route?

A

oral → need absorption of the drug before the drug concentration increases/shows up in the body

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9
Q

What is extravascular drug administration?

A

administration of a drug that is not put into the blood but still want it to reach systemic circulation

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10
Q

What is the advantage of extravascular drug administration?

A

ease of administration → especially with patient compliance

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11
Q

What are the disadvantages of extravascular drug administration?

A
  1. takes time for drug to enter systemic circulation following administration
  2. some drug may be lost during the absorption process
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12
Q

What is the relationship between drug variability and response variability?

A

variability of drug = variability in response

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13
Q

What are examples of immediate release products?

A
  1. solids → tablets and capsules (most common route of administration)
  2. liquids → syrups, elixirs, suspensions, and emulsions
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14
Q

What are examples of modified release products?

A
  1. extended release → controlled release (that approximates zero order release in which constant drug is released over time) and sustained release (maintains drug release but not at a constant rate)
  2. delayed release → delay before the drug is released (common example is enteric coated aspirin)
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15
Q

What are the different graphs of concentration v time for different oral drug formulations?

A
  1. immediate release → sharp slope early on, reaches Cmax the quickest
  2. sustained release → slope is a little less steep with decreased Cmax and takes longer to reach Cmax
  3. controlled release → looks like IV infusion with a steady state
  4. delayed release → looks exactly like immediate release but with a lag time
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16
Q

What is the comparison between an oral dose and IV bolus dose?

A

oral dose has absorption delays and reduced magnitude of the peak compared with an equal IV bolus dose → Cmax is affected by absorption which is why oral route has a decreased Cmax because it takes longer for absorption

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17
Q

What are the different phases of oral administration?

A
  1. absorption phase → rate coming into the body is faster than rate coming out
  2. postabsorption/distribution phase → right past the peak
  3. elimination phase → rate leaving the body is faster than going in
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18
Q

What happens at the peak (Cmax) of an oral administration?

A

elimination rate = absorption rate

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19
Q

What are the PK parameters of absorption?

A
  1. 1st order absorption rate constant (ka)
  2. lag time of absorption (tlag)
  3. extent of absorption (F)
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20
Q

For an IV bolus dose, what is the rate of elimination?

A

dA/dt = -kel*A (in which kel is first order and units are /time and A is the amount in the body which changes with time) → all of drug is put in at t=0

21
Q

For an IV infusion, what is the rate of elimination?

A

dA/dt = Rinf-kel*A (in which Rinf is the rate of infusion and follows zero order) → not all of drug is put in at once

22
Q

For oral administration, what is the rate of elimination?

A

dA/dt = rate of absorption - kelA = kaAabs - kel*A (in which ka is first order and Aabs is the amount in absorption compartment that changes with time)

23
Q

For oral administration, when is the fastest rate of absorption?

A

t=0

24
Q

Rate of absorption is given by what?

A

ka*Aabs

25
Q

Rate of elimination is given by what?

A

kel*A

26
Q

At the different phases, what is the absorption rate compared to the elimination rate?

A
  1. absorption phase → kaAabs > kelA
  2. Cmax → kaAabs = kelA
  3. post absorption phase → kaAabs < kelA
27
Q

What is the complexity of drug absorption following an oral dose?

A
  1. drug needs to be dissolved in GI to be absorbed
  2. drug needs to pass the gut wall to get into systemic circulation
  3. the rate of drug absorption represents the net result of all of these processes!!
28
Q

Both ka and kel are what?

A

they are both constants so they don’t change over time

29
Q

What happens when ka decreases (slower rate of absorption)?

A
  1. delays tpeak and decreases Cmax
  2. bioavailability and CL are unchanged
  3. AUCs are identical
30
Q

What happens when ka < kel?

A
  1. absorption rate limits elimination → the decline of drug in plasma reflects absorption rather than elimination
  2. flip flop kinetics (like sustained release products) → since elimination is faster, elimination cannot be faster than what is being absorbed so when Cmax is passed, what determined the rate of elimination is the rate of absorption (half life of elimination is half life of absorption)
31
Q

What is the lag time of absorption (tlag)?

A
  1. absorption of drug after a single oral dose may not start immediately (the lag time is when the concentration is 0 at the beginning)
  2. the lag time (tlag) can be anywhere from a few minutes to many hours
32
Q

What are some complexities that alter tlag and alter drug absorption?

A
  1. disintegration/dissolution
  2. GI motility
  3. blood flow
  4. drug transport
33
Q

Why is Cmax lower for the oral dose compared to IV administration?

A

the oral dose takes longer to be absorbed and Cmax is affected by absorption

34
Q

Why is the AUC lower for the oral dose?

A

oral doses have a decreased Cmax because of the longer absorption time which means AUC would also be decreased

35
Q

Is ka less than or greater than kel following the oral dose of aspirin?

A

During the absorption phase, ka is greater. At Cmax, ka = kel. During the post absorption phase, kel is greater.

36
Q

What is the fraction of drug absorbed (F)?

A
  1. the portion of dose administered that reaches the systemic circulation (aka fraction of dose that makes it to the systemic circulation and can be greater than 1)
  2. IV administration → F=1
  3. extravascular route → F can range from 0 to 1
37
Q

What are some factors that can affect F?

A
  1. dissolution
  2. gut wall permeation
  3. active transport
  4. metabolism
  5. biliary excretion
38
Q

What is the main source that transports the drug throughout the body?

A

portal vein

39
Q

What are some terms that are often used to describe F (fraction of drug absorbed)?

A
  1. fraction of drug absorbed → best definition
  2. available drug
  3. bioavailability (technically incorrect)
40
Q

What is the FDA definition of bioavailability?

A

the rate and extent to which the active ingredient or active moiety is absorbed from a drug product and becomes available at the site of action → the fraction of drug absorbed is NOT a measure for the rate of absorption

41
Q

What is bioavailability?

A
  1. an important component of bioequivalence assessments
  2. bioequivalence is part of the approval process for generic drugs
  3. cmax, tpeak, and F are the primary PK parameters assessed for bioavailability studies
42
Q

What is the most important thing to note about F?

A

it tells you extent, not the rate!!

43
Q

How is F calculated?

A

from IV bolus dose → CL = kelVd = dose/AUC
for dose following extravascular administration → CL = Fdose / AUC
AND since CL is the same following oral or IV dose, the equations can be combined

44
Q

What is the equation for absolute bioavailability (aka fraction of drug absorbed, F)?

A

F = (AUCoral/doseoral) / (AUCiv/doseiv)

45
Q

What can be used to estimate F?

A

cumulative urine data can be used

46
Q

How is relative bioavailability calculated?

A

Relative F = (AUCgeneric/dosegeneric) / (AUCbrand/dosebrand)
(if plasma concentrations are measured to show generic is equivalent to brand)

47
Q

If total urine is collected, then what is fe (fraction of drug excreted in the urine)?

A

fe = Ae/(F*dose) in which Ae is the amount of drug excreted in urine

48
Q

What is relative bioavailability if we assume fe remains constant for the brand drug A and the generic drug B?

A

Relative bioavailability = Fdruga/Fdrugb = (Aea/dosea) / (Aeb/doseb)

49
Q

What value do we want relative bioavailability to be?

A

1

Pharmacokinetics (14 decks)

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