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Physiology and Pharmacology > Pharmacokinectics > Flashcards

Pharmacokinectics Flashcards

1
Q

What is Pharmacokinetics?

A

What the body does to the body

Branch of pharmacology

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2
Q

What is a drug?

A

Any substance used for the treatment, relief, diagnosis or prevention (prophylaxis) of disease

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3
Q

What are the 3 main sources of drugs?

A

1) plant origin- e.g. Digoxin (foxglove)
2) animal origin- e.g. Insulin previously from pigs
3) mineral origin- e.g. Magnesium

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4
Q

What are the 2 main routes of administration?

A

Parenteral

Enteral

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5
Q

What is the definition of enteral?

A

Anything involving the digestive tract

From the mouth to the rectum

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6
Q

What is the definition of parenteral?

A

‘To avoid the gut’

Any route other than via the GI tract

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7
Q

What are examples of enteral administration?

A

Oral

Rectal

Sublingual (under the tongue)

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8
Q

What are examples of parenteral administration?

A

Subcutaneous

Intramuscular

Intravenous

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9
Q

What are the 4 stages of pharmacokinetics?

A

1) absorption
2) distribution
3) metabolism
4) excretion

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10
Q

What is drug absorption?

A

From administration though to the time it reaches the tissues and so is available to us

May involve getting into the circulation

Oral drugs must be converted into a solution via Dissolution to be absorbed

Quicker a drug is converted into soluble state, faster it can be absorbed across cell membranes

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11
Q

What processes allow absorption across cell membranes?

A

Passive transport and active transport

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12
Q

What is the process of passive transport?

A

Requires no energy (ATP)

Movement of substances down conc. gradient from high to low concentration

E.g. High in GI tract to low in bloodstream (oral drugs)

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13
Q

What is the process of active transport?

A

Requires energy (ATP)

Movement of substances from a low to a high conc. (against conc. gradient)

E.g. Levodopa- treats Parkinson’s disease

Carrier molecules may be involved

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14
Q

How can distribution take place?

A

Bloodstream transports the drug to its site of action

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15
Q

How does blood flow to a tissue affect a distribution?

A

Drugs will ultimately get to all tissues

Drugs initially may reach higher conc. in tissues with a good blood supply e.g. Brain/heart

Reduced flow to tissues and organs affect distribution

Blood brain supply (prevents bacteria/toxins entering the brain)

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16
Q

What is the function of the brain blood barrier?

A

Prevents any substances from entering the CNS

Some substances are blocked from entering brain tissue- acts as protective mechanism- prevents harmful substances entering the brain

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17
Q

What is a free drug?

A

The part of the drug that is not bound

Can exert its effects on tissues

Distribution depends on properties of the drugs e.g. Lipid solubility etc

The free drug is the only active part- small enough to leave the bloodstream

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18
Q

What is metabolism?

A

Involves transforming drug so it is more water-soluble and can be excreted

Main site- liver (other tissues involved- plasma, kidneys, lungs and intestinal mucosa)

19
Q

What is the function of metabolism?

A

Drugs metabolised into inactive metabolites and excreted

Some metabolites are already active so exert own action and then undergo further metabolism or are excreted unchanged

Some metabolites require altering to become active

20
Q

What is the function of liver cells in metabolism?

A

Attempt to break down the drugs into constituent parts so they can be eliminated

21
Q

What is the First Pass Effect?

A

Shows effect liver metabolism has had on the drug during its first passage through the liver (how much drug has been broken down in the liver)

How much of the drug has been inactivated

The drug always has to first pass through the liver to be broken down before it is able to circulate the rest of the body

22
Q

What are the 3 determinations that can be made from the first pass effect?

A

1) amount of drug reaching general circulation
2) half-life of drug (time taken for half the drug to be eliminated from the plasma)
3) whether the drug undergoes ‘biotransformation’

23
Q

What is biotransformation?

A

The conversion of molecules from one form to another within an organism, often associated with change in pharmacologic activity

May involve drug being changed from an inactive to an active state

‘Pro drugs’

24
Q

What is excretion?

A

Involve active or inactive drugs

Requires removal from site of action

Main organ- kidney

25
Q

What are the main organs involved in elimination of drugs?

A 
Kidney 
Gut 
Skin
Lungs 
Salivary glands 
Sweat glands
26
Q

What is bioavailability?

A

Used to describe the fraction of an administration dose of the drug reaching the systematic circulation

E.g. If bioavailability is 50%, half the dose reaches the systematic circulation

If low- higher dose is required and excess will remain in the GI tract

27
Q

What factors affect bioavailability?

A

Route of administration

Properties of drugs

Absorption

Blood flow to administration site

First pass effect

28
Q

What is the definition of onset?

A

Time from administration to when the therapeutic effect occurs and is affected by routes of administration and pharmacokinetics

29
Q

What is the effect of intravenous administration?

A

Gives the quickest route

Most brief pain control

Most CNS side effects

30
Q

What is the effect of oral administration?

A

Maximises duration of analgesia

Minimises CNS side effects

Longest time to onset of relief

31
Q

What dictates the timings of repeat doses?

A

1) rate of absorption
2) metabolism of the drug
3) excretion

32
Q

What is the definition of steady state?

A

Reached when rate of infusion is equal to rate of elimination

33
Q

What is the function of modified released drugs?

A

Designed to slowly release drug into GI tract over a period of time

34
Q

What are the benefits of modified release oral preparations?

A

1) dose frequency is reduced- increased compliance
2) peak plasma level reduced- less side effects
3) less peaks and troughs in plasma levels- more sustained therapeutic effect

35
Q

Give 2 examples of modified release preparations…

A

Propranolol

Ibuprofen

36
Q

What is the definition of therapeutic range?

A

Optimum plasma levels in which it has its therapeutic effect

37
Q

What is the therapeutic window?

A

Describes levels in plasma at which a drug can act

Aiming for drug concentration to be within this window

Narrow- require monitoring

38
Q

What does MTC and MEC stand for?

A

MTC- maximum tolerated concentration

MEC- minimum effective concentration

39
Q

What does Iatrogenic mean?

A

Illness caused by medicine, examination or treatment

40
Q

How do pharmacokinetic changes affect older people?

A

Most important is the reduction of kidney function so care must be taken with drug toxicity and its effect on the kidney

41
Q

How do pharmacodynamics affect old people?

A

They are more sensitive to drugs acting in CNS and drugs causing side effects in the stomach/intestine

42
Q

What is drug tolerance?

A

Describes the decrease in pharmacological effect when a drug is given repeatedly

Causing progressively higher doses required to produce the same effects

Various pharmacokinetics/pharmacodynamics mechanisms- tolerance

E.g. PK mechanisms- increased metabolism of drug

E.g. PD mechanisms- reduced receptor numbers at cell surface

43
Q

What does the term drug dependence mean?

A

A compulsion/compulsive need to take a drug in order to function normally (even if it causes harm)

Lead to withdrawal symptoms e.g. Diahorrea, shivering, muscle ache, dilated pupils, sweating and abdominal cramps

Body adapts to the drug and so stabilises

Causes the body to overcompensate for the drug which is no longer present

Physiology and Pharmacology (35 decks)

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