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CMOD/PCM- Block 2 > Pharm: Pharmacokinetics II > Flashcards

Pharm: Pharmacokinetics II Flashcards

1
Q

In the study of a new drug, the volume of distribution is found to be 80L and the clearance 4L/hr. What is the approximate half-life of the drug?

A

by my calculations: 10hr.

But in Sweatman’s slides, of the given answer choices, 14 is closest to 10

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2
Q

Continuous infusion of lidocaine is given to a 70kg individual. Pharmacokinetic parameters for lidocaine are:
CL = 9 mL/min/kg
Vd = 70 L
half life = 2hr
How long will it take to reach 87.5% of steady state levels?

A

Three half lives, or: 6hr.
Recall it takes 4-5 half lives to reach steady state (that is, 100% of steady state levels). After the first half life you’re at 50%; after 2nd you’re at 75%; after third you’re at 87.5% - therefore it takes 3 half-lives. This half-life pattern is the same whether moving up toward steady state levels, or down in elimination.

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3
Q

Two drugs (A and B) act on the same receptor and reduce BP by the same amount at the following doses:
Drug A - 120mg
Drug B - 15mg
Does this imply that Drug A has a higher TI, has a lower bioavailability, has a shorter half-life, is less efficacious, or is less potent than Drug B?

A

That drug A is less potent than drug B

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4
Q

A new oral Abx is being tests and has the following pharmacokinetic parameters:
Vd = 60L
CL = 30 ml/min
F = 50%
Half-life = 23hrs
Target plasma concentration for effective bactericidal action is 2mg/L. What is the appropriate loading dose?

A 
LD = (Css*Vd)/F
LD = (2mg/L*60L)/50%
LD = 240mg
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5
Q

In a drug study of 1,000 subjects, half receive the active drug and half receive placebo. The physicians and patients are blind to treatment. Which step of the drug development process is this most likely?

A

Phase III clinical trial

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6
Q

The fraction of an administered drug that reaches the circulation is known as ____.

A

bioavailability

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7
Q

A 3rd year medical student is trying to determine the steady-state plasma concentration of an experimental anti-arrhythmic agent. Treatment was initiated 6hrs earlier at a rate of 3mg/min. The student knows the following pharmacokinetic parameters:
Vd = 120 L
CL = 0.6 L/min
Half-life = 3hr
If the infusion rate remains untouched, what will the steady-state plasma drug level be?

A 
Answer: 5mg/L
Formula:
Css = IR/CL    (where IR=infusion rate)
Css = (3mg/min) / (0.6L/min)
Css = 5mg/L

*There is no bioavailability term in this equation because it’s being administered IV, so F=1

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8
Q

What term best describes the margin of safety for any drug?

  • affinity
  • efficacy
  • potency
  • therapeutic index
  • variability
A

therapeutic index

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9
Q

If the serum concentration of drug X is found to be 4mg/L following a single intravenous dose of 112mg, the drug most likely distributes where?

A

intracellular fluid
Vd = 112mg / (4mg/L) = 28 L
28 is about 70% of total body water, therefore it makes sense that the distribution is in the intracellular fluid compartment

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10
Q

To calculate the loading dose of a drug, one must know the target plasma concentration and what other parameter?

A

volume of distribution

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11
Q

Bioavailability of drugs is important because…

A

it determines what fraction of the administered dose actually reaches the circulation

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12
Q

Renal clearance of a drug is determined to be 60mL/min. (normal value = 125-130mL/min) Which of the following might explain this finding?

  • extensive tubular secretion
  • drug isn’t bound to plasma proteins
  • extensive tubular reabsorption
  • low molecular weight
A

That would be, “Harsher punishment for parole violators, Stan.” - no shoot I mean “extensive tubular reasborption,” Trevor.
And, world peace.

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13
Q

For a drug exhibiting saturated elimination kinetics, the biological half-life is affected by what variable characteristic of the drug?

A

the dose administered

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14
Q

A dental patient has been given aspirin to provide pain relief following a dental procedure. This drug is a weak acid with a pKa of 3.5. If the pH of the stomach is 2.5, what percentage of the drug dose will be in the non-ionized (lipid soluble) form?

A 
about 90%
*From Henderson-Hasselbalch equation:
pH - pKa = log [A-]/[HA]
2.3 - 3.5 = log [A-]/[HA]
-1 = log [A-]/[HA]
log^-1(-1) = 0.1
Then set the non-ionized form arbitrarily to 1:
0.1 = 0.1/1 = [A-]/[HA]
Where [A-] = 0.1, then you can see that the ratio is 10% ionized, 90% protonated state
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15
Q

Which of the following is the most appropriate route of drug delivery for a 35yoF being treated at home for N/V during a viral illness?

  • inhalation
  • oral
  • rectal
  • IV
  • sublingual
A
  • rectal

- sublingual

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16
Q

Which of the following is the most appropriate route of drug delivery for a 55yoM brought to the ER with recurrent tonic/clonic seizures following a head injury?

  • inhalation
  • oral
  • rectal
  • IV
  • sublingual
A
  • IV
17
Q

A drug that possesses a high likelihood of producing addiction in patients is known as a ____ drug.

A

Class II

18
Q

Which of the following is not required to be accomplished before a drug can be tested in humans?

  • acute animal toxicity studies
  • reproductive toxicity testing in animals
  • approval of an investigational new drug application
  • approval of a new drug application
A

-approval of a new drug application

19
Q

Which of the following is NOT a reliable source of information regarding drug pharmacology?

  • Physician’s Desk reference
  • package insert
  • National Formulary
  • US Pharmacopoeia
  • Wikipedia
A
  • Wikipedia

um. ..okay….like we’re not going to look there…

20
Q

Tavlinephrine is a drug with first-order kinetics following IV administration. Therefore, the rate of elimination is proportional to _____________.

A

plasma concentration of the drug.

21
Q

Bob is receiving Drug A that has high affinity for plasma proteins, but in doses that doesn’t fully saturate all binding sites. Drug Y is added to the regimen; this one also binds with high affinity to the same plasma proteins and is administered at doses 100X above maximal binding capacity. What are the consequences of this polypharmacy with regard to Drug A?

A

tissue levels of Drug A will increase - this is a property of drug distribution; if not bound in the plasma it will redistribute to the tissues

22
Q

Which of the following precludes the prescription of a proprietary (brand name) drug?

  • the FDA hasn’t approved its use for a specific indication
  • a generic form is available
  • the drug has high abuse potential
  • the bioavailability is
A

None of the options restricts a physician’s prerogative to prescribe the agent

23
Q

What does it mean for drug concentration when the pH and the drug’s pKa are equal?

A

It means 50% of the drug is ionized and 50% is non-ionized

24
Q

For a weak acid drug: When the pH is lower than a drug’s pKa, is it more likely to be protonated or less protonated?

A

protonated

25
Q

When a weak base drug is in an environment that is more acidic than it’s pKa, it is more likely to be protonated or non-protonated?

A

protonated, which for a base is an ionized state

26
Q

What does saturation kinetics mean, in the context of drug elimination?

A

the mechanism to eliminate the drug is at maximum capacity, therefore only a certain amount of drug can be removed per unit time

27
Q

For drugs that obey saturation kinetics, a constant ____ of drug can be removed per unit time.

A

amount

*NOT constant fraction

28
Q

True or false: for drugs obeying saturation kinetics, the biological half-life is dependent on the dose administered.

A

True - the higher the dose, the longer the half-life for clearance.

29
Q

For Drug X:
Vd = 40L/kg
CL = 0.5L/hr/kg
If the patient is a 60kg woman, how long is the expected half-life of the drug in this individual?

A

56 hr

= Vd/CL * .7

30
Q

How do you calculate clearance from dose and area under the curve (AUC)?

A

CL = dose / AUC

AUC will be in units of mg/L per hour, when the plot is mg/L vs. time (hr)

31
Q

If Drug Y causes a reduction in plasma concentration of Drug X, regardless of route of administration for drug X, what’s the most likely pharmacokinetic parameter that Drug Y is reducing?

  • absorption
  • bioavailability
  • half-life
  • metabolism
A

A: half-life. If it reduces the half life then more of drug x is cleared faster.

  • reducing bioavailability only refers to what’s available for the tissues; it could be in plasma but bound and not free
  • if it reduces metabolism that would increase the amount of drug X

CMOD/PCM- Block 2 (41 decks)

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