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PHAR2002 > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

Pharmacokinetics

A

Time course of drugs in body

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2
Q

Drug targets

A
  1. receptors
  2. ion channels
  3. enzymes - inhibit, false substitution, pro-drug
  4. transporters - inhibit, false substitution
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3
Q

When you take a drug, steps are:

A
  1. liberation
  2. absorbed
  3. enters plasma
    - excreted
    - bound to plasma
    - tissue resevoir if hydrophobic
    - non-related receptors may bond
    - > wanted = therapeutic site of action
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4
Q

A polin

A

A pore which allows bigger molecules but is normally gated

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5
Q

Pinocytosis

A

Vesicle fuses with others -> might not need to cross memvrane

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6
Q

Main way a drug crosses lipid membrane

A

Conc. different -> has to be liphophilic enough to go through but not so much to stay in membrane

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7
Q

Partition coefficient =

A

[drug] chlorophorm / [drug] water

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8
Q

What does partition coefficient tell us

A

Solubility -> charged/ uncharged (acid/base)

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9
Q

At 50% ionisation [HA] / [A] =

A

1

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10
Q

Urine can change ____

A

pH

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11
Q

Dosage needs to be controlled in pregnant women because

A

drugs can accumulate in foetus -> ion-trapping from kidney to placenta

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12
Q

Why is enteral G.I. a good method of drug intake?

A

Doesn’t need to be sterile, convenient

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13
Q

Enteral G.I. intake includes:

A
  • oral
  • under tongue (pareteral) - can be thought of as transdermal
  • rectum
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14
Q

Every time the drug circulates it goes through which organ?

A

Liver

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15
Q

Why is buccal/ sublingual/ rectal preferred?

A

Directly to general circulation so avoids first pass

  • > useful with younger children
  • useful for some irritants
  • when patient unable to take drug -> vomiting/ unconscious
  • supposetery
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16
Q

Outline oral intake

A

Lipid soluble + ion -> weak acids may be bsorbed

- surface area -> stomach is small so mainly in intestines where peristalsis helps dissolve tablet

17
Q

What can affect oral intake of drugs?

A

Gut contents - decrease drug. conc. + impaired access to mucosa
Diarrhoea - babies
e.g. tetracycline + milk - chemical interaction

18
Q

Bioavailability =

A

How much drug reaches systemic circulation

F = area under the curve/ dose

19
Q

What are the steps from dose to systemic circ.

A

stomach - gut - first pass

20
Q

Bioequivalence

A

Same 500g gives same amount of drug into plasma from 1 drug brand to the next

21
Q

What is a 100% bioavailable way of introducing a drug?

A

Intravascular -> venous/arterial

22
Q

Drug distribution

A

Reversible transfer of a drug from 1 location to another in the body depending on physiochemical nature of drug

23
Q

4 types of distribution pattern:

A
  1. Drug remains in vascular system
  2. Low molecular weight - soluble compounds are uniformly distributed throughout the body of water
  3. Specific concentration in 1 or more tissues
  4. Non-uniform distribution based on lipid/water solubility
24
Q

Apparent volume fo distribution

A

VD = The volume of fluid the drug would occupy if it were evenly distributed through the volume at concentration in plasma

= Dose/ Cp 0

25
Q

VD = 3-5

A

Distribution in vascular system

26
Q

VD = 30-50

A

Total body of water

27
Q

Drug binding

A

The less a drug is bound the more effective it is

28
Q

Binding is:

A

non-specific and reversible

29
Q

Albumin

A

Plasma protein that binds to acidic drugs

30
Q

Glycoproteins bind to

A

basic drugs

31
Q

Consequences of protein binding:

A
  1. Activity decreases
  2. Absorption - free conc. low so constant conc. gradient -> sink effect
  3. Distribution - restricted to binding protein areas
  4. Storage - dissociates when free drug conc. low
  5. Elimination - depends on rate limiting step of elimination -> half-life can be longer if less filtered through renal glomerulus or shorter if more brought to liver
  6. Interactions - low specificity -> competition for binding sites -> more free drug so higher conc. can be toxic e.g. warfarin by acidic drugs
32
Q

Tissue perfusion limits

A

transport

33
Q

Biotransformation phases

A
  1. Oxidations, reductions, hydrolyses

2. Conjugations - liver - major site of drug metabolism

34
Q

Mechanism of elimination in nephron:

A
  1. Glomerular filtraion
    - molecules > 60kg/mol
    - passively filtrates blood (20%)
  2. Tubulor secretion (80%)
    - enzymes transporting drugs from plasma to urine
    - > competition reduces renal clearance
    - > clearance rate increases by 650 mill
  3. Tubular reabsorption
    - acidic/basic increases reabsorption of weak acid/base
35
Q

Hepatic excretion

A

Bile is produced at a rate of 0.5-1 l/day and is a major route of excretion for a few drugs (e.g.
cromoglycate) and rather more metabolites (e.g. morphine glucuronide). Drug excreted in the bile
may be reabsorbed in the intestine and so enter an enterohepatic circulation. A significant
proportion of drug in the body may be within this enteric pool.

36
Q

First order elimination

A

Rate of elimination is proportional to the plasma concentration of the drug, Cp. Cp will decline exponentially when drug administration is stopped. Under these conditions it is possible to define a plasma halflife - the time taken for the plasma concentration to fall by 50%. The plasma half-life is thus an important measure of the speed of drug elimination.

37
Q

Zero order elimination

A

Rate of elimination is independent of the plasma concentration, a situation
which arises when the process of elimination (e.g. active secretion) has become saturated.
(Michaelis-Menten kinetics apply in this situation.)

38
Q

ClT =

A

Kel x VD = [t0.5 =0.693/ClT x VD ]

39
Q

Metabolism in liver:

A
  1. More reactive groups

2. large compounds accumulate + conjugate

PHAR2002 (14 decks)

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