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BPM1 Exam 2 - Foundations to Medicine 2 > FTM 56-57 - Clinical Pharmacokinetics 1 & 2 > Flashcards

FTM 56-57 - Clinical Pharmacokinetics 1 & 2 Flashcards

1
Q

What is the plasma concentration of a drug a function of?

A
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2
Q

What are the three most important pharmacokinetic parameters?

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3
Q

How do you calculate a drug’s volume of distribution

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4
Q

What is the Vd of a drug essentially?

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5
Q

What kinds of drugs tend to have a higher Vd? Lower Vd?

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6
Q

What is the main use of the Vd value?

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7
Q

What is the only time the amount of drug in the body is known accurately?

A

Immediately after the drug has been given IV, before it can be metabolised

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8
Q

Describe how a plasma [drug] vs time plot would look for an IV bolus of a drug.

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9
Q

What is the C0 for a drug and how is it determined?

A

The C0 for a drug is a theoretical value of what the concentration of that drug would be at time zero if distribution occurred instantly. It is determined by plotting the log of plasma [drug] vs time which will provide two relatively straight lines representing the distribution phase and elimination phase. The elimination phase line is then followed back to the y-axis to find C0

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10
Q

What is the equation for Vd?

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11
Q

What equation is used to ascertain the dose of a drug needed to achieve a target concentration quickly?

A

Dose = Vd x TC

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12
Q

What is the equation used to determine the clearance rate of a drug?

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13
Q

What is the Km for a drug?

A

The plasma [drug] at which that drugs elimination rate is half maximal.

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14
Q

What is the equation for the rate of elimination of a drug? How can this be simplified?

A

Rate of elimination = (Vmax x C)/(Km + C)

For most drugs the C <<< Km which means it can omitted from the denominator giving us rate of elimination = (Vmax x C)/Km

Clearance is a constant at CL = Vmax/Km so the RE equation simplifies to

RE = CL x C

This is true only for the drugs with a therapeutic plasma concentration well below Km

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15
Q

For the drugs that follow first order kinetics, how can their initial concentration be calculated?

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16
Q

For first order kinetic drugs, how do their concentrations decay over time?

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17
Q

Why are half-lifes so important in pharmacology?

A

For first-order kinetic drugs (which is most of them) the half-life is constant no matter the plasma [drug]. Half-life will also determine the rate at which plasma [drug] rises during constant infusion.

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18
Q

What is a drugs Css?

A

At a given infusion rate, every first order kinetics drug will reach a steady plasma concentration (Css) over time.

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19
Q

How can a drug’s half-life be used to determine the plasma [drug] after a certain period of time of constant IV infusion?

A
20
Q

During a constant IV infustion of a drug, what percentage of Css is reached after each half-life has passed?

A
21
Q

What equation is used to determine the half-life of a drug?

A
22
Q

About how long does it take for a drug to reach Css?

A

4 half-lives

23
Q

About how long does it take for a drug to effectively eliminated from the body?

A

4 half-lives

24
Q

What does doubling the infusion rate of a drug do to its Css?

A

It doubles it

25
Q

T/F - Increasing the infusion rate of a drug will decrease the time it takes for that drug to reach Css? Explain

A

False, because doubling the infusion rate also double the Css and that drug’s half-life has not changed.

26
Q

List the factors that affect a drugs half-life and how they affect it.

A
27
Q

Why do some drugs exhibit saturation kinetics? What are these drugs? How is their rate of elimination calculated?

A

For drugs that exhibit saturation kinetics, the body metabolises and excretes them very inefficiently. This means their C is usually way higher than the drugs Km. This means that RE = (Vmax x C)/(Km + C) simplifies to RE = (Vmax x C)/C or simply RE = Vmax

Therefore, for the drugs: Ethanol, Phenytoin and Aspirin (at high doses) their rate of elimination is simply their Vmax no matter what plasma concentration

28
Q

When is a drugs clearance constant and when isn’t it? Why?

A

A drug’s clearance rate is constant when first order kinetics apply. This is because CL=RE/[plasma] and the ratio of RE to [plasma] never changes.

A drug’s clearance rate is not constant when saturation kinetics apply. This is because the RE (Vmax) remains constant while the [plasma] changes. Therefore, CL will increase as [plasma] drops.

29
Q

What equation is used to determine CL during saturation kinetics? Show how it is derived.

A
30
Q

Is half-life still constant for drugs that exhibit saturation kinetics? Explain

A

No, because t1/2 = (0.693 x Vd)/CL and CL is not constant for drugs that exhibit saturation kinetics

31
Q

What is a maintenance and loading dose?

A
32
Q

What three things need to be know about a drug to develop a dosage regimen?

A
33
Q

What is normally the goal of maintenance dose?

A

To replace the amount of drug that was eliminated since the last dose

34
Q

What equation is used to determine the dosing rate for a continuously infused drug.

A

F is bioavailability

35
Q

If a drug is to be given intermittently, how is the dosage determined?

A
36
Q

How is Css determined for a continuous IV infusion?

A
37
Q

What is the Css directly proportional to for drugs exhibiting first-order kinetics? Why?

A

The infusion rate because Css = IR/CL and CL is constant for drugs exhibiting first-order kinetics.

38
Q

What is a loading dose for and how is it calculated?

A
39
Q

How does [plasma] vs time graph appear for a drug givin orally?

A
40
Q

How does a [plasma] vs time graph look for a drug given orally in a slow release tablet

A
41
Q

How does a [plsma] vs time graph appear for an IV bolus injection?

A
42
Q

How does a [plasma] vs time graph appear for multiple IV injections?

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43
Q
A
44
Q

IV theophylline was given to a patient at an infusion rate of 28 mg/h/70 Kg to relieve an acute bronchial asthma attack. The clinician now wants to maintain the current plasma concentration using oral theophylline taken every 12 hours. The bioavailability of this oral tablet is 96%. What dose should the clinician prescribe?

A
45
Q
A

BPM1 Exam 2 - Foundations to Medicine 2 (29 decks)

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