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Year 2 > Metabolism + Excretion > Flashcards

Metabolism + Excretion Flashcards

1
Q

How does enzyme saturation effect the rate of removal of a drug + what order is this

A

Makes it constant (a further increase in enzyme conc. does not effect rate of removal)
0

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2
Q

What drug follows 0 order kinetics

A

Ethanal if alcohol dehydrogenase is saturated

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3
Q

Define half-life

A

Time taken for a conc. to reduce by a half

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4
Q

What is half-life in the context of drug elimination

A

Elimination rate from plasma

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5
Q

Why dow e measure elimination rate from plasma

A

Easy to measure

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6
Q

Define bioavailability

A

Fraction of administered drug that reaches the systemic circulation un-altered

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7
Q

Why do IV drugs have bioavailability (F) of 1

A

100% of the drug reaches circulation

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8
Q

Why would oral drugs have F<1

A

Incompletely absorbed or undergo first pass metabolism

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9
Q

How does bioavailability effect prescriptions

A

If drug has F=0.1 than we need an oral dose of 10*0.1

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10
Q

How is bioavailability measured

A

AUC oral/ AUC IV

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11
Q

What factor effects rate of distribution of water-soluble drugs

A

Rate of passage across membranes

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12
Q

What factor affects rate of distribution of lipid soluble drugs

A

Blood flow to tissues that accumulate the drug

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13
Q

Why is extent of drug distribution important

A

Determines total amount of drug that has to be administered to produce a particular plasma conc.

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14
Q

How is extent of drug distribution measured

A

Volume of distribution (Vd)

Vd = total amount of drug in body/plasma conc.

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15
Q

What does a low Vd indicate

A

Drug is confined to circulatory volume

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16
Q

What does a high Vd indicate

A

Drug is mostly distributed in total body water

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17
Q

Define clearance

A

Volume of blood or plasma cleared of drug per unit time

18
Q

What is the plasma conc. of a drug with a high Vd

A

Low

19
Q

How is rate of elimination related to Vd

A

Rate of elimination is inversely proportional to Vd

20
Q

Formula for Rate constant of elimination

A

K= CL/Vd

21
Q

Consequence of a CL of 0

A

Drug would not be removes and plasma conc. would remain at equilibrium indefinitely

22
Q

Formula for clearance for IV drugs

A

Dose/AUC for IV

23
Q

Formula for clearance for oral drugs less than 1

A

Dose x F/AUC

24
Q

Why do we use repeated drug doses

A

Maintain constant drug concentration in blood

25
Q

What is Css

A

Steady State - balance between drug input and elimination

26
Q

Difference in Css between injection and infusion

A

Injection - Rapid increase then rapid decrease before another dose is given

Infusion - Increase gets gradually slower until it reaches a peak and then decreases

27
Q

How many half-live are needed to reach 95% of Css IV infusion

A

4-5

28
Q

Consequence of a drug with slow elimination

A

Takes a while to reach steady state and will accumulate high plasma conc. before elimination rate rises to match drug infusion

29
Q

Consequence of a drug with a high Vd

A

Delay in reaching Css as half life depends on Vd

30
Q

When is Css achieved for IV infusion

A

When rate of elimination = rate of infusion

Rate of elimination = CL x Css

31
Q

How can we calculate plasma clearance

A

CL = Rate of infusion / Css

32
Q

How can we calculate Css

A

Rate of infusion/CL

33
Q

Formula for Dose

A

Dose = Bioavailability/Time interval

34
Q

What happens to the rate of administration when steady state is reached

A

Rate of administration = rate of elimination

35
Q

Formula for rate of elimination

A

Rate of elimination = CL x drug conc.

36
Q

D x F/t =?

A

D x F/t = CL x Css

Css =( Dxf/t)/CL

37
Q

Effect of drug with long half life on Css

A

Takes longer time to reach Css

38
Q

How can we overcome a long half life causing a long time to reach Css

A

Give a high initial dose to load the system and shortens time to steady state

39
Q

Formula for loading dose

A

Css x Vd

40
Q

How can the steady state be maintained after the loading dose

A

Css = D x F/t x CL

Year 2 (155 decks)

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