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Pharmacology > Pharmacokinetics - Drug Elimination > Flashcards

Pharmacokinetics - Drug Elimination Flashcards

1
Q

What is between the MEC and the MTC

A

The therapeutic window

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2
Q

What is the therapeutic ratio

A

TR = MTC/MEC

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3
Q

In relation to the TR what makes a drug safer

A

A safer drug has a larger therapeutic window
With a high therapeutic ratio such a penicillins
Unsafe Drs have a lower ratio such as barbiturates

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4
Q

What a re pharmacokinetics

A 
Mathematical analysis of all drug disposition factors
Abs
Dist 
Metab 
Excretion
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5
Q

What is a rough pathway of constituents affecting the pharmao okinetics

A

DoseD oral admin which is abs at rate Kabs to single well stirred compartment of volume Vd
Then removed drug by elimination Kel rate

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6
Q

If a drug is added rapidly by IV what si by passed

A

Abs is by passed so the initial conc = dose/Vd.

Come at later time dept on Kel

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7
Q

Most drugs exhibit first order kinetics

A

Where rate elim Kel is directly proportional to drug concentration
Meaning the conc drives the elim

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8
Q

What happens to the drug conc after admin

A

Falls exponentially

Ct = C0e^( Kel.t)

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9
Q

What si the half life

A

Time taken for Ct to fall 50%
Inversely related to Kel
T1/2 = 0.69/Kel

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10
Q

What is clearance

A

Vol plasma cleared of drug per unit time
Constant relating the rate of elim to plasma conc
Applies only to drugs which exhibit first order kinetics

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11
Q

What is the rate of elim eqn

A

Rage of elim = clearance x Cp l/HR

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12
Q

What does clearance determine

A

The Maintenance dose rate (dose per unit time required to maintain a given plasma conc)

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13
Q

What is steady state

A

When rate of elim = rate of admin

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14
Q

Cl is a sum of

A

All clearance processes

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15
Q

For drugs that exhibit first order kinetics the steady state and plasma conc

A

Linearly related to infusion rate

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16
Q

The time to reach steady state is determined by

A

Half life but not infusions rate

17
Q

Approx when does steady state reach

A

About 5 half lives

18
Q

What si drug dosing orally like

A

Dosing to steady state orally intermittent nvolves sam principles as IV but lasts conc fluctuates about an average steady state value

19
Q

For steady state orally what is the eqn

A

Css(average) = (F x dose) / ( Clp x dosage interval)

F = oral bioavailability fraction of drug admin that enters the systemic circ

20
Q

How many half lives to steady state

A

Five half lives

21
Q

What si the volume of distribution

A

Volume which a drug appears to be distributed with a concentration equal to that of plasma

Proportionality constant relating the plasma conc to the amount of drug In the body

22
Q

What’s is the eqn for the amount of drug in th bodyb

A

Ab = Vd x Cp

23
Q

What is a loading dose

A

Initial higher dose of a drug given at the beginning of a course of treatment before stepping down to a lower maintenance dose

24
Q

What sis loading dose used for

A

Employed to decrease time to steady state for drugs with long half lives (phenytoin)

25
Q

How can the loading dose be estimated from the Vd of the drug? For IV admin and oral admin

A

IV admin
LD = Vd x target Cp

Oral admin
LD = ( Vd x target Cp)/F

26
Q

When can Vd vary?

A 
In disease (heart fail, liver disease)
Therefore adjustment of dosage may be needed especially for drugs with low tr
27
Q

What si the half life

A

Time for the conc of a drug in plasma (amount drug in body) to halve

28
Q

What does the half life give an index of

A

The time course of drug accumulation

Time course of drug elim

29
Q

What sit he Half life dept on

A

Vd and clearance what sit he eqn for half life

30
Q

What is the eqn for half life

A

t(1/2) = (0.693 x Vd)/Cl

31
Q

What is zero order

A 
Few drugs( ethanol) 
Eliminate at constant rate
Nor proportional to the conc
32
Q

Elimination is initially

A

Zero order and change to first order

33
Q

How does a drug achieve an effect

A

By having a critical concentration in the plasma which is between the min effective conc and the max tolerated conc

Pharmacology (4 decks)

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