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Foundations of Medicine > pharmacodynamics and pharmacokinetics > Flashcards

pharmacodynamics and pharmacokinetics Flashcards

1
Q

why are pharmacokinetics and pharmacodynamics studied ?

A

To allow individualized patient drug therapy and decreased risk of adverse effects while maximizing pharmacological response to medication.

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2
Q

What is pharmacodynamics?

A

What the drug does to the body.

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3
Q

What is pharmacokinetics?

A

The science of the rate of movement of a drug. It is governed by the absorption, distribution, metabolism and elimination. If these are known then the dose, route of administration, frequency and likelihood of side effects can be predicted.

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4
Q

Describe the graph showing the change in drug blood concentrations over time.

A

Drug concentrations must be kept within strict limits to keep the drug effective but not toxic.
Tmax is the time taken to get to the peak concentration
Cmax is the peak concentration
AUC is the area under the graph.

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5
Q

What does the AUC tell you?

A

The bioavailability of the drug.

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6
Q

How can bioavailability be determined?

A

By comparing the plasma concentration of a drug administered in one way with the plasma concentration of the drug being administered through IV.

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7
Q

What is the bioavailability of a drug delivered through IV?

A

100%

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8
Q

What is bioavailability effected by?

A
  • Drug form (liquid etc)
  • Ability of a drug to pass the phycological barriers
  • GI effects (i.e. gut motility and first pass metabolism)
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9
Q

What is gut motility ?

A

The gut motility of a drug will effect the speed of gastric emptying. This will effect the rate of absorption. It is altered by food, drugs, illness, etc.

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10
Q

What is first pass metabolism?

A

The metabolism of drugs prior to retching the circulation. It can occur in the gut lumen(acid or enzymes) or gut wall (metabolic enzymes) or liver. (cytochrome P450).

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11
Q

What are the different ways in which drugs can be delivered?

A
  • Tablets or capsules
  • Solutions and suspensions
  • Ointments and creams
  • Inhalation
  • Injections
  • Suppositories
  • Pessaries
  • Novel mechanisms
  • Parental preparations
  • Surgical implants
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12
Q

How do tablets and capsules work?

A 
Taken regularly 
Have modified release 
A prodrug 
Enteric coating 
Rate limiting step is the breakdown 
High accuracy 
Reproducible 
Stable 
Coat protects again stomach acid 
Prolonged or delayed release formulas cut down on the number of time medication must be taken 
Sustained release allows for a longer period of time within the therapeutic range.
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13
Q

How do solutions and suspensions work?

A

Useful in those who cant swallow

Small volume

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14
Q

How do ointments and creams work?

A

Percutaneous.

local and systemic effects (i.e. topical steroids)

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15
Q

How do inhaled drugs work?

A

get directly to the lungs

take education

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16
Q

How do injections work?

A

Intramuscular drugs may be insoluble or oil based.

Subcutaneous injections are useful for insulin delivery.

17
Q

What is the dose of a drug given dependant on?

A

BNF guidance
Weight
Age
renal and hepatic function

18
Q

If a patient is started on one brand of a drug can then be swapped brand?

A

No

19
Q

What is a prodrug ?

A

A drug synthesised as an inactive form and needs to be metabolised to become active.

20
Q

What are some of the main factors in absorption?

A
  • Lipid solubility. A drug that is not lipid soluble may not be absorbed at all i.e. gentamicin.
  • Ionisation. Most drugs are weak acids or bases. Only un-ionised forms of the drug can be absorbed.
21
Q

What does it mean for a drug to be absorbed?

A

A drug is in the blood stream.

22
Q

What type of delivery system has first passed metabolism?

A

Oral

23
Q

What delivery systems do not have any first passed metabolism ?

A 
Subcutaneous 
Intramuscular 
Inhalation 
nasal 
Transdermal
24
Q

By what processes are drugs absorbed?

A 
Passive diffusion (most common) 
Protein mediated transporters 
Filtration 
Bulk flow (common way in which dugs cross capillary walls) 
Facilitated diffusion 
Ion-pair transport 
endocytosis 
active transport
25
Q

What is distribution?

A

The reversible process by which drugs are transferred between the blood and extra vascular fluids and tissue of the body.

26
Q

What does the distribution of a drug depend on?

A 
The plasma protein binding 
Tissue perfusion 
membrane characterises 
Transport mechanisms 
disease and other drugs 
elimination
27
Q

What is the apparent volume of distribution?

A

The volume of plasma that would be found in a person if the drugs was present thought-out the body in the same concentration. Measured in litres per kg.

28
Q

What is clearance?

A

The theoretical volume from which a drug is completely removed over a period of time. It is measured in ml per min. It is a measurement of elimination.

29
Q

What is half-life?

A

The time taken for the drug concentration in the blood to decline to half the current value.

30
Q

What is the drug metabolism?

A

The biochemical modification of pharmaceutical substance by living organised through specialized enzymatic activity. This is essential because it limits the life of drugs within the body, converting lipid soluble non-polar substances into water soluble polar substances to that they can undergo excretion. Therefore, the purpose of drug metabolism is to deactivate compounds, increase water solubility and aid exertion.

31
Q

What is drug elimination?

A

Drugs are excreted through the kidneys using;
Glomerular filtration. This filters 190 litres of fluid a day filtering any unbound drugs as long as they are not too large or highly charged. Drugs that reduce glomerular filtration can result in toxicity.
Passive tubular reabsorption. As the filtrate moves down the renal tubule any drug present is concentrated as water is reabsorbed. Passive diffusion along the concentration gradient allows the drug to move back through the tubule into the circulation. Passive diffusion occurs in the distal tubule and collecting duct. Only un-ionised drugs such as weak acids are reabsorbed. Can also be affected by renal failure.
Active tubular secretion. Some drugs are actively secreted into the proximal tubule. Used for acidic and basic compounds and cationic and anionic drugs.

32
Q

What is the first phase of drug metabolism?

A

Phase 1 – Drug undergoes activation or deactivation. This phase involved hydrolysis, oxidation or reduction which increases the polarity and provides an active site for phase 2. The cytochrome P450 enzymes are very important. CYP1A2 acts on theophylline (induced by smoking therefore smokers require a higher dose compared to non-smokers), CYP2D6 acts on codeine (metabolises antidepressants, antipsychotics and converts codeine to morphine) and CY3A4 acts on cyclosporine (is found in the liver metabolises a wide range of drugs).

33
Q

What is the second phase in drug metabolism?

A

Phase 2 – Drug is converted to conjugated products. Conjugation is the process of making something more water soluble and therefore enhances its excretion. It involved the addition of a glucuronic acid, glutathione, sulphate or acetate group.

34
Q

What is biliary secretion?

A

The liver secretes 1 litre of bile a day. Drugs may be passively or actively secreted into the bile. Biliary secretion accounts for 5-95% of drug elimination for many drugs. A number of drugs are then reabsorbed from the bile into the circulation. This is called entero-hepatic circulation. It continues until the drug is metabolised in the liver or excreted by the kidneys

35
Q

Many drugs work work by inducing enzymes. Expand

A

This requires enzyme synthesis and is done by drugs such as phenytoin, Rifampin and St.Johns wort. These drugs take a long time to act.

36
Q

Many drugs work by inhibiting enzymes. Expand

A

This are very fast acting. I.e. Grapefruit juice, protease inhibitors and azoles.

37
Q

What enzymes are involved in excreting drugs?

A

Group of CYP enzymes convert drugs into a recognisable from so that they can be broken down.

38
Q

Examples of CYP enzymes involved in drug metabolism

A

CYP2D6 - Metabolise more than 65 drugs inc. antidepressants.
CYP2C9 - Metabolise 16 drug i.e. warfarin, phenytoin and NSAIDs
CYP2C19 - Metabolise antidepressants, warfarin.
These are all polymorphism drugs.

Foundations of Medicine (25 decks)

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