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Basic Pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

Pharmacokinetics

A

Effect of drug on body

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2
Q

Why does ADME need to be calculated?

A

Ensure dose results in correct plasma concentration in all individuals

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3
Q

Absorption

A

Transfer of exogenous compounds from site of administrations o systemic circulation

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4
Q

What must a drug be able to do to be absorbed?

What molecules are the best for this?

A

Cross cell membranes = lipid soluble and unionised

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5
Q

Where to more drugs get absorbed

a) oral route - stomach
b) oral route - SI

A

b

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6
Q

What heavily control rate of absorption in the stomach?

A

Rate of gastric emptying

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7
Q

Why is the SI a more common site of absorption?

A

Large, highly vascularised SA

Enterocytes on epithelium contain metabolising enzymes and transporters

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8
Q

Advantages of oral admin

A

Cheap

No skill = patient can do it

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9
Q

Disadvantages of oral admin

A

Slower rate fo absorption
Dependent on pH
1st pass metabolism

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10
Q

4 factors affecting GI absorption

What do they all impact?

A

Rate of gastric emptying
pH (poor absorption of strong acids/bases)
Physcio-chemical interactions (tetracycline binds to Ca rich foods)
Particle size and formation

Bioavailability

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11
Q

Bioavailability?

A

Fraction of administered dose entering circulation

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12
Q

1st pass metabolism?

A

Metabolism in intestine and liver before reaching systemic circulation

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13
Q

How is absorption calculated from concentration time graph?

A

Area under the curve

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14
Q

Bioavailability (F) of IV vs any other route?

A

IV - F = 1
Any other F<1
No first pass metabolism in IV

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15
Q

Limitations of bioavailability?

A

Doesn’t consider individual variation e.g. gut motility

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16
Q

Cmax and Tmax?

A

Maximum concentration after admin

Time that Cmax occurs

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17
Q

Advantages of sublingual administration?

A

Fast response
Utilises drainage from mouth the sup vena cava so goes straight to intestine
Avoids its pass metabolism

18
Q

Why is rectal/vaginal a possible route?

A

Bypasses first pass metabolism
Rich blood supply
Useful for someone how is vomiting/diarrhoea

19
Q

Advantages of IV admin?

A

Bypass 1st pass metabolsim

Rapid response - straight into systemic

20
Q

Disadvantages of IV?

A 
Painful
Needs a professional
Adverse reactions
expensive
Infection
21
Q

Advantages of intramuscular admin?

A

Local effect = good fro LA

Faster absorption than oral

22
Q

3 ways a drug can pass through membrane (diffusion)?

A

Passive diffusion down concentration gradient
Diffusion through aqueous channel
Carriers

23
Q

Many drugs are weak acids/bases.

What does this mean about ionisation state?

A

Unionised and ionised form dependent on pH

24
Q

How is strength of acid calculated?

A

pKa

25
Q

When pH=pKa how much of drug is ionised?

A

50%

26
Q

At what pH is a weak acid and weak base unionised?

A

Weak acid unionised at low pH (acidic)

Weak base unionised at high pH (basic)

27
Q

pH partitioning?

A

Acidic drugs accumulate in basic areas (where they are ionised so cannot pass through membranes)
Basic drugs accumulate in acidic areas

28
Q

Aspirin is a weak acid

Is it mostly ionised or unsigned in the stomach?

A

Unionised

29
Q

Distribution

A

Reversible transfer from systemic circulation to tissue

30
Q

What is distribution dependent upon?

A

Ability to cross membrane, blood flow to tissues, extend of plasma binding proteins

31
Q

When equilibrium between tissue and plasma is reached, plasma concentration decreases as elimination begins.
What occurs to tissue?

A

As plasma concentration decreases, drug diffuses back into plasma down the concentration gradient, this gets eliminated keeping the plasma concentration low so it keeps diffusing out = eliminated at same rate as plasma

32
Q

What effects rate of distribution?

A

Membrane permeability

Vascularisation

33
Q

What effects extent of distribution?

A

pKa of drug
Lipid solubility
Plasma binding protein
Tissue binding

34
Q

What happens to drugs with high molecular weight or degree of plasma protein binding?

A

They are not distributed well because they cannot pass through the membrane

35
Q

What does amount of plasma protein binding depend upon?

A

Concentration of free drug and concentration of plasma protein
Affinity for the free drug to the protein

36
Q

What causes tissue binding?

A

Composition of drug e.g. lipid soluble drugs bind to fat

Cellular components e.g. tetracycline binds teeth and bone as they contain Ca2+

37
Q

What distribution parameter shows distribution between plasma and tissue?

A

Vd = volume of distribution

38
Q

How is Vd calculated?

A

Total amount of drug in body/concentration of drug in plasma

39
Q

If the drug is confined to plasma Vd =

a) low
b) high

A

a

40
Q

If drug is not lipid soluble so is distributed in extracellular compartments the Vd will be

a) higher than drug confined to plasma but lower than a well distributed drug
b) lower than drug in plasma but higher than a well distributed drug?

A

a

Basic Pharmacology (12 decks)

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