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Medical Pharmacology Exam 1 > Drug Dosing > Flashcards

Drug Dosing Flashcards

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USMLE® Step 1 flashcards
1
Q

When you adminster a drug and graph its concentration plasma, the resulting graph looks like an upside down half moon. What does the left side (ascending) represent? What about the right (descending)?

A

Ascending - Absorption

Descending - Metabolism and excretion

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2
Q

What is the threshold that has to be reached before you start seeing effects? What 2 “ranges” is it between on a drug dosage chart?

A

Minimum effective concentration

Between the therapeutic and ineffective ranges

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3
Q

Regarding how a drug will work, what is more important; the plasma concentration or the administered dose.?

A

Plasma conc. Tells you what will get to receptors

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4
Q

The fraction of Administered Drug Reaching the Systemic Circulation in its Active Form is _. The symbol for this is _. What route of admin has the highest? What route of admin has the lowest?

A

Bioavailability
F
IV
Oral

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5
Q

What are the 3 major factors that affect oral bioavailabilty that were mentioned in the notes?

A

Gastric emptying time (oral)
Intestinal transit time (oral)
First pass effect (oral)

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6
Q

How is bioavailability measured graphically? In a situation where bioavailability is low, how do you rectify that?

A

Measure bioavailability by measuring AUC

Increase the administered dose

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7
Q

Increasing the administered dose of a drug will change what 3 specific parameters?

A

Onset of action
Duration of action
Apparent efficacy

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8
Q

What are 2 factors that will affect the rate of availability?

A

Dissolution of drug into absorbable form

Blood flow

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9
Q

What is the definition of volume of distribution? What is its symbol? What is the formula?

A

The apparent volume in which a drug dissolves
Vd

Vd = Amount (of drug in body) / C-plasma (or Cp)

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10
Q

To calculate the Vd, how do you determine the plasma concentration?

A

Plot all the descending plasma concentrations, change Y axis to log scale and then extrapolate to time zero (Cp0)

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11
Q

What is the biggest volume in the body? What type of drugs will have the largest volume of distribution? Why?

A

Total body water
Lipophillic drugs
Lipophillic drugs generally excluded from plasma, low concentrations in formula -> high Vd

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12
Q

What are the 4 factors mentioned that affect Vd?

A

Body weight
Body composition
Age
Disease

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13
Q

The elimination of Active Drug after its Distribution is called _. What is the symbol? What is the formula?

A

Clearance
CL
CL = Rate of elimination / Cp

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14
Q

What are the 2 components of clearance?

A

Excretion

Metabolism

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15
Q

What are the 2 factors that determine rate of elimination?

A

Amount of drug delivered to elimination mechanism

Capacity of elimination mechanism

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16
Q

A capacity limited elimination system is termed _. This mean that there is more _ than _ [capacity / drug].

A

Zero order

Drug than capacity

17
Q

For a zero order system, capacity is _ [limited / not limited]. Rate of elimination is _ [dependent / independent] of plasma concentration. Clearance is [constant / variable]

A

Limited
Independent
Variable

18
Q

What happens if you increase the plasma concentration of the drug in a zero order elimination system?

A

Nothing, The capacity is already maxed out

19
Q

A delivery limited elimination system is termed _. This mean that there is more _ than _ [capacity / drug].

A

First order

capacity than drug

20
Q

For a first order system, capacity is _ [limited / not limited]. Rate of elimination is _ [dependent / independent] of plasma concentration. Clearance is [constant / variable]

A

Not limited
Dependent
Constant

21
Q

First order, vs zero order. Which is going to give you a fixed amount of removed drug per unit time? Which will give you a fixed percent of removed drug per unit time?

A

Fixed amount - Zero order

Fixed percent - First order

22
Q

The first order plasma concentration vs time graph is curved. How can you linearize it?

A

Change the Y axis to a log scale

23
Q

What is the example of a drug that follows a zero order mechanism? Under what conditions does a zero order elimination become a first order elimination?

A

Ethanol follows zero order

At levels below saturation, zero order becomes first order

24
Q

What are the 4 factors affecting clearance?

A

Body weight
Blood flow to organs
Age
Disease

25
Q

What is the difference between a maintenance and a loading dose?

A

Loading - one time bolus

Maintenance - subsequent doses to maintain Cpss

26
Q

What is the objective if the loading dose? What is the main factor affecting loading dose i.e. what might cause the loading dose to change?

A

To fill the volume of distribution (areas where drug can “hide”) to quickly reach therapeutic ranges in plasma
Volume of distribution

27
Q

What is the objective of the maintenance dose? What is the main factor affecting maintenance dose?

A

Replace drug lost to elimination

Dependent on elimination

28
Q

Simply put, the loading dose is dependent of _ while the maintenance dose is dependent on _

A

Volume of distribution

Elimination

29
Q

What is the major factor affecting dosing frequency? How is it calculated i.e. what is the formula?

A

Plasma half life

t1/2 = 0.693 x Vd/CL

30
Q

Approxinmately how many half lifes does it take to reach steady state levels?

A

4-5 half lifes

31
Q

Both renal and hepatic disease will affect what 2 pharmacokinetic variables?

A

Decreases clearance

Prolongs half life

32
Q

What pharmacokinetic variable will hepatic disease affect that renal disease won’t? Why (2)?

A

Increases oral bioavailability

  • Decreased first pass
  • Decreased plasma protein (made in liver)
33
Q

Under what 2 conditions would a target concentration strategy for drug dosing be used?

A

an effect cannot be readily determined

drug has a low T.I.

34
Q

Under what condition would a maximal dose strategy be used?

A

A drug that has a high therapeutic index

Medical Pharmacology Exam 1 (15 decks)

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