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Pharmacology > Drugs - Postabsorption > Flashcards

Drugs - Postabsorption Flashcards

0
Q

What 3 things effect the extent of distribution?

A

Lipid-solubility of drug
Blood flow to tissue/organ
Binding of drugs to proteins

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1
Q

Once the drug is in the bloodstream, what does distribution involve?

A

Transfer of the drug in and out of various tissues in the body from the bloodstream.

This is a 2 way process - forward and reverse

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2
Q

What organ receives the greatest blood flow (and therefore receives the drug most quickly)?

A

Kidneys

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3
Q

What is protein binding? Why can this be a good thing?

A

Where free drug binds to proteins in the plasma, such as albumin.
This reduces the amount of free drug. Only free drug can diffuse across membranes to have an effect as the proteins are too big.
This is good for drugs like warfarin (an anti-coagulant) as it prevents too much free drug causing internal bleeding.

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4
Q

When thinking about protein binding, why is it important that you know every single drug a patient is taking before administering a new one?

A

As drugs like warfarin rely on protein binding to ensure that the levels in the blood are not too high, we need to know if there are potentially any other drugs competing for the proteins.

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5
Q

What are the 2 most common routes of absorption for drugs?

A

Passive Diffusion

Facilitated Transport

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6
Q

What route of administration has the most rapid effect? Is it reversible?

A

I.V.

No

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7
Q

What 2 processes are involved in drug removal?

A

Metabolism

Excretion

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8
Q

What does lipophilic mean?

A

This is where drugs recirculate around and around the body, constantly having an effect.

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9
Q

What is drug metabolism?

A

The enzyme-mediated conversion of a lipid-soluble compound into a more water-soluble one.

This prevents the drug constantly re-circulating and allows us to excrete it

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10
Q

Which is the main organ where drug metabolism takes place?

Which part of this organ?

A

The liver.

The smooth endoplasmic reticulum.

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11
Q

Other than the liver, can you name up to 5 other sites that metabolise drugs?

A 
Kidney
Lung
GI Tract
Brain
Plasma
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12
Q

If a patient has liver damage, what should we do when administering a drug?

A

Reduce the dosage as according to the BNF.

This is because they cannot metabolise as well as a healthy patient and the normal level would be toxic

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13
Q

Other than the liver, what other organ can have an effect on metabolism if damaged?

A

The kidneys

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14
Q

What are the two phases of metabolism called?

A

Phase 1

Phase 2

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15
Q

In metabolism, does Phase 2 always follow Phase 1?

A

No. Usually, but not always

16
Q

What happens in Phase 1 of metabolism?

A

The chemical structure of the drug is modified (to be less lipid and more water soluble)
Usually prepares the drugs for Phase 2

17
Q

Sometimes Phase 1 can result in pharmacological activation.

What is this?

A

Where the product becomes more chemically reactive than the original ‘parent’ drug = more potent
e.g. pro drugs - prednisone becomes Prednisolone
codeine becomes morphine, GTN becomes nitric oxide

18
Q

Do all drugs rely on pharmacological activation to have an effect?

A

No, but some do - such as prednisone, codeine and GTN

19
Q

What happens in Phase 2 of metabolism?

A

The drug is ‘conjugated’ to large molecules such as amino acids and sulphate groups. It then becomes:
water-soluble so can be easily excreted
increases in molecular weight so can’t fit in target site
Undergoes pharmacological inactivation

20
Q

What is pharmacological inactivation?

A

Where the drug:
decreases in receptor affinity
and excretion is enhanced

21
Q

What effect can alcohol or carbamazepine have on drug metabolising enzymes?

A

They can induce liver enzymes which may be used to metabolise a particular drug - this will reduce its effectiveness

22
Q

What effect can fluoxetine or grapefruit juice have on drug metabolising enzymes?

A

They can inhibit liver enzymes. This means it can prolong the effect of a drug as it will not be metabolised as quickly, thereby resulting in toxic levels

23
Q

How are water-soluble drugs and drug metabolites excreted?

List the 4 ways in order of excretion amount

A

Urine
Bile
Faeces
Lungs/skin/sweat

24
Q

If the blood flow to the kidneys is increased and plasma protein binding is reduced, what will happen?

A

Increased drug excretion.

So, if a patient has kidney failure this can be manipulated artificially too.

25
Q

What is the therapeutic response of most drugs related to?

A

The level of drug in the plasma

Large amount = big effect

26
Q

What is the half-life of a drug?

A

The time it takes for the amount of drug in the body to decrease to one half of the peak level.
This is the duration of action for most drugs and is the rate at which are drugs are eliminated from the body.

27
Q

If the half-life of a drug is 3 days, how long is it until the drug is eliminated from the body?

A

6 days

28
Q

What percentage of drugs are eliminated after 5 half-lives? (Regardless of dose or route of administration).
97%, 95% or 85%?

A

97%

It is useful to know this when administering a new drug, in order to avoid drug interactions.

29
Q

What can we use to estimate how long it will take for a toxic concentration of drug to leave the body?

A

The half-life of a drug and how many half lives it takes for it to be eliminated (97% of drugs is 5 half lives)

30
Q

What is the therapeutic window?

A

The gap between the minimum toxic concentration of drug and the maximum therapeutic concentration of drug

31
Q

Most drug have a large therapeutic window.

Name an example of a drug with a narrow therapeutic window and what this means for nursing

A

Warfarin and phenytoin have narrow therapeutic windows.

When administering these kinds of drugs it is important to monitor the patient carefully - this is known as therapeutic drug monitoring

32
Q

What is therapeutic dosing? (without a loaded dose)

A

This is where a person starts taking their drug and it accumulates to a certain level, to which it plateaus as they carry on taking their drug at certain intervals.

33
Q

What is therapeutic dosing? (with a loaded dose)

A

This is where the individual is initially given a large amount of a drug for it to instantly hit the therapeutic window. The dosage is then reduced so that it stays within the window.
This is done when a quick effect is needed.

34
Q

What is toxic dosing?

What is sub-therapeutic dosing?

A

When too much drug is administered.

When not enough drug is administered.

35
Q

In relation to half-life, when are most drugs given?

A

Drugs tend to be given every half-life

36
Q

What happens to the half-life of a drug if a patient has hepatic or renal disease?

A

It increases and drug concentrations may reach toxic levels

Pharmacology (13 decks)

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