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Pharm Block 1 > Drug Elimination and Multiple Dosing > Flashcards

Drug Elimination and Multiple Dosing Flashcards

1
Q

In two-compartment drug distribution, after the distribution phase, what kind of elimination do you get?

A

monoexponential elimination

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2
Q

What kind of half life do you get with monoexponential elimination?

A

a constant half life!

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3
Q

Define volume of distribution (Vd)

A

the theoretical volume of fluid into which the total drug administered would have to be diluted to produce the concentration in plasma

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4
Q

What is the volume of distribution a measure of?

A

how evenly a drug is distributed in the body

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5
Q

What does Vd relate?

A

dose (amount, mg/kg) to plasma concentration (mg/L)

Vd = Dose/C0

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6
Q

Why is repetitive dosing necessary?

A

it takes 4-6 half lives to reach a steady state

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7
Q

What is a loading dose?

A

If a drug takes a long time to reach therapeutic levels, then a higher dose (the loading dose) may be given initially before dropping down to a lower maintenance dose.

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8
Q

What are the three variables used to calculate loading dose?

A

Cp - peak desired concentration of drug

Vd - volume of distribution

F - bioavailability

loading dose = Cp * Vd / F

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9
Q

What is not reduced by the loading dose?

A

time required to reach the steady state (still takes 4-6 half lives)

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10
Q

Define maintenance dosing

A

maintains a steady state of a drug in the body

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11
Q

What is a maintenance dose based on?

A

replacing the amount of drug cleared from the body since the previous drug administration

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12
Q

What is the primary determinant for calculating the maintenance dose?

A

CL

MD = CL* TC * T / F

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13
Q

In a loading dose, what is the target concentration?

A

Cp - the highest concentration of drug you will see in plasma (the “peak”)

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14
Q

In a maintenance dose, what is the target concentration?

A

between the peak and trough - not the peak as it was for the loading dose

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15
Q

What is elimination clearance?

A

CLe - irreversible drug removal from the plasma through an eliminating organ

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16
Q

What is intercompartmental clearance?

A

CLi - drug distribution between plasma and tissues, a bidirectional process

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17
Q

at steady state, what is the maintenance dosing rate equal to?

A

rate of elimination = CLe * TC

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18
Q

What is steady-state concentration a function of?

A

dosing rate and elimination clearance

Css = (dosing rate * F) / CL

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19
Q

How long before steady state is achieved?

A

4-6 half lives

20
Q

What is time to steady state independent of?

A

dosage

21
Q

What are plasma drug fluctuations proportional to?

A

dosage interval/half life

22
Q

What is steady state concentration proportional to in continuous IV infusion?

A

proportional to infusion rate

infusion rate = CL * Css

23
Q

What can clearance be estimated by in continuous IV administration?

A

infusion rate and steady state plasma conc.

CL = I/Css

24
Q

What is 1st-order elimination (kinetics)?

A

the elimination rate of the drug is a constant fraction of the drug remaining in the body per unit time (rather than a constant amount of drug per unit time)

most drugs used clinically

25
Q

What is zero-order kinetics?

A

a fixed amount of drug is metabolized per unit time

26
Q

What kind of drugs may display zero-order kinetics, and when would it happen?

A

drugs eliminated primarily by metabolism

When metabolic pathways are saturated, metabolism occurs at a fixed rate (it does not change in proportion to drug concentration)

27
Q

What two drugs are examples of zero-order elimination?

A

phenytoin, ethanol

28
Q

What is not constant in zero order, that is is 1st order?

A

half life

29
Q

name 9 drugs that may exhibit zero-order kinetics

A 
Aspirin
Ethanol
Heparin
Phenylbutazone
Phenytoin
Salicylates
Theophylline
Tolbutamide
Warfarin
30
Q

Define dose-dependent kinetics

A

When a drug’s elimination is mediated predominantly by metabolism, its elimination will tend to follow first-order kinetics when concentrations are well below the KM of the metabolic enzymes, but will follow zero-order kinetics at doses that greatly exceed the KM of the metabolic enzymes.

31
Q

define and name the units of elimination clearance

A

Volume of plasma cleared of drug per unit time.

Units are ml/min or L/hr (“flow”)

32
Q

For elimination clearance, where can drug elimination occur through?

A

kidneys, liver, lung, and other organs

33
Q

What is total clearance equal to?

A

CLrenal + CLhepatin + CLother

34
Q

What is elimination half life?

A

time to eliminate 50% of the body content of the drug

t1/2 = 0.69 Vd / CL

35
Q

What is time to steady state dependent on?

A

only dependent of the half life - not the dose!

36
Q

How can you reduce the dosing rate in renal insufficiency?

A

reducing the dose

increasing the dosing interval

both

37
Q

What is creatinine clearance rate, and what is it used for?

A

Creatinine clearance rate (CrCL) is the volume of blood plasma that is cleared of creatinine per unit time and is the most commonly used measure for approximating the glomerular filtration rate (GFR) - a relative measure of how well the kidney is functioning

38
Q

What are the determinants of hepatic drug clearance?

A

hepatic blood flow

plasma protein binding

intrinsic clearance

39
Q

What is restrictive hepatic clearance?

A

drugs with low hepatic extraction, and thus little first pass metabolism when given orally

40
Q

what will have a greater influence on hepatic clearance in drugs with low hepatic clearance?

A

changes in binding or drug metabolism/excretion activity will have a greater effect of hepatic clearance than changes in liver blood flow. (capacity limited clearance)

41
Q

What are two examples of drugs with low hepatic extraction?

A

warfarin, phenytoin

42
Q

What is non-restrictive hepatic clearance?

A

drugs with high hepatic extraction

43
Q

What does non-restrictive hepatic clearance exhibit

A

flow-dependent clearance

44
Q

What is flow dependent clearance?

A

Hepatic clearance is sensitive to changes in liver blood flow and less sensitive to alterations in binding or intrinsic clearance.

conditions that reduce hepatic blood flow (CHF, hypotension) will reduce hepatic clearance.

45
Q

What are two examples of drugs with high hepatic extraction?

A

lidocaine, propranolol

Pharm Block 1 (8 decks)

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