Pharmacokinetics Flashcards

1
Q

Definition of pharmacokinetics

A

What the body does to the drug

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2
Q

Definition of pharmacodynamics

A

What the drug does to the body

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3
Q

Definition of PK/PD

A

The relationship between pharmacokinetics and pharmacodynamics

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4
Q

Definition of half life

A

How quickly half the drug is removed from the body

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5
Q

Definition of bioavailability (F)

A

How much of the drug enters the systematic circulation

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6
Q

Definition of clearance (Cl)

A

Volume of plasma from which a substance is completely removed/unit of time

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7
Q

Definition of volume of distribution (Vd)

A

Amount of drug in the body to the conc of the drug measured in a biological fluid

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8
Q

Definition of zero order kinetics

A

Drug is cleared at a constant rate, regardless of the concentration

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9
Q

Definition of first order kinectics

A

Drug is cleared at a rate which is dependent on the conc in the body so generally doesnt accumulate in the blood

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10
Q

Definition of extra hepatic clearance

A

Drug is cleared by other organs as well as the liver, eg, kidneys

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11
Q

Definition of therapeutic window

A

A range of doses that produces a therapeutic response without any significant adverse effects

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12
Q

Definition of safety window

A

Same as the therapeutic window

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13
Q

What is the difference between pharmacokinetics and pharmacodynamics

A

Pharmacokinetics, what the body does to the drug

Pharmacodynamics, what the drug does to the body

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14
Q

What are the 5 drug properties and what do they mean

A

Dose, how much to take

Half life, how quickly half the drug is removed from the system

F (bioavailability), amount of drug that enters the systematic circulation

Cl (clearance), Volume of plasma from which a substance is totally removed/unit of time

Vd (volume of distribution), Amount of drug in the body to the conc of drug measured in a biological fluid

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15
Q

Describe zero order kinetics
What are the potential dangers
What are 2 examples of zero order kinetic drugs

A

Drug is cleared at a constant rate, regardless of the conc
Can accumulate and occur in overdose

Phenytoin, alcohol as their elimination process is saturated

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16
Q

Describe first order kinetics

What are the positives

A

Drug is cleared at a rate which is dependent on the conc in the body
Generally does not accumulate in the blood

17
Q

Describe how drugs equilibrate in a 1 compartment system

A

Singly kinetically homogenous entity
Drug achieves instantaneous distribution and equilibration
Monophonic decline

18
Q

Describe how drugs equilibrate in a 2 compartment system (central and peripheral)

A

Distribution takes time to equilibrate between 2 systems

Biphasic decline

19
Q

What is a half life

A

The time taken for the plasma conc of a drug to fall by half

20
Q

How to calculate the elimination rate constant (k) for a first order reaction

A

dA/dt = -kA

A=Ao exp(-kt)

A=amount of drug
Ao=initial amount of drug
k=elimination rate constant
t= time

Plot Ln[A] against time to get a linear line
K=gradient
Ao=e^y intercept

21
Q

What is the relationship between half life and k

A

t1/2 = In2/k

22
Q

What is absorption?
What is the absorption rate constant
What affects the rate of absorption in each route

A

Process by which a drug moves into the site of action
Absorption rate constant is 1st order

Oral absorption : aqueous solution => lipid diffusion => permeation

Can be solubility (dissolution rate) and pH (pKa) dependent

Solubility can be pH dependent
-GI tract starts acidic but becomes more alkali

23
Q

How would you calculate the volume of distribution

How is the plasma conc linked to the amount of drug

A

Vd (L) =total amount of drug dosed/plasma conc of drug

Plasma conc, not necessarily the same as the amount of drug, drugs can attach to the sides => Vd increases as a result

24
Q

What does metabolism aim to do

Give 2 examples

A

Modify the drug so it is more soluble
Via oxidation
-Propanolol => 4-hydroxypropanolol

Via conjugations so the whole new molecule is soluble
-Chloramphenicol => chloramphenicol-O-glucaronide

25
What is excretion and what limit its rate What are the properties of clearance What are the equations for clearance
The clearance of a drug (volume of plasma cleared of a drug per unit time) Can be limited by organ blood flow Can include saturable processes Products can be metabolized at the same time Clearance is additive Cl total = Cl hepatic + Cl renal + Cl metabolic Cl (L/h)= k x Vd Cl = dose/AUC Cl=Q x Eh
26
How is hepatic clearance calculated | What does it mean when Eh = 1
Extraction ratio (Eh) = difference between amount of drug that enters and leaves the liver/amount of drug that enters the liver Eh=1, drug is completely cleared by the liver so non enters the systemic circulation
27
What is the rate of human blood flow in the liver (Q) | How does the flow relate to the clearance
1.4L/min | Faster flow => faster clearance
28
How does hepatic blood flow and extraction ratio relate to clearance What is the max hepatic clearance
Cl = Q x Eh 1.4L/min
29
How does clearance relate to bioavailability | What happens if total clearance is greater than Q?
All GI blood passes into hepatic portal system before it enters the systemic circulation Maximal oral bioavailability (F) = 1 -Eh The higher the hepatic clearance, the lower the bioavailability If total clearance > Q the there is extra hepatic clearance
30
What organs can take part in extra hepatic clearance
Kidneys and other organs | All organs that can take part can have a different extraction ratio => difference amounts of clearance
31
What is the renal blood flow in a human
1.1L/min
32
How does the route of dosage affect the bioavailability | What is bioavailability limited by
Fraction of unchanged drug reaching the systemic circulation IV = 100% PO = can vary due to -Limited absorption -Limited by gut, hepatic metabolism/excretion
33
How to calculate bioavailability
F= Area under curve for oral dosing/area under curve for IV dosing
34
What is the minimum effective conc
The smallest dose needed to produce a therapeutic effect
35
What controls the PK/PD relationship
The action of a drug controls it As you increase the amount of drug up to a certain point, the effect does not change due to the sigmoid curve in pharmacodynamics