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ASC306 > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

The 4 processes of ADME determine what?

A

the plasma concentration of drug over time

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2
Q

What is parenteral administration? eg?

A

route of admin which does not involve the intestinal tract

eg. IV, IM, SC

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3
Q

3 factors affecting drug absorption…

A
  • route of admin
  • drug formulation
  • chemistry of drug
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4
Q

Where are drugs transported?

A

aqueous phase of blood plasma

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5
Q

Apart from IV admin., ADME must involve what process?

A

transfer across cell membranes

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6
Q

What aspect of the lipid bilayer creates the hydrophobic interior?

A

fatty acyl side chains

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7
Q

What are the factors influencing rate of absorption?

A
  • biological membranes (rate depends on lipid solubility)
  • molecular size and shape + solubility at site of absorption
  • degree of ionisation (most drugs are weak acids or bases and present as both ionised + unionised forms)
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8
Q

Can ionised/unionised molecules freely cross lipid cell membranes? why?

A

ionised - no as they are hydrophilic

unionised - yes as they are lipid soluble (lipophilic)

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9
Q

Weak acid is most unionisedin a fluid with … pH?

A

acidic eg. weak acid absorbed in stomach

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10
Q

Weak base is most unionisedin a fluid with … pH?

A

basic eg. weak base absorbed in small intestines

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11
Q

What does pH partition mean?

A

only uncharged forms of weak acids or bases can diffuse across lipid membranes

  • protonated form for weak acid
  • unprotonated form for weak base
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12
Q

Weak acids/bases accumulate where?

A

weak acids - compartments of high pH

weak bases - compartments of low pH

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13
Q

Drugs are mainly absorbed by …?

A

passive diffusion (down concentration gradients)

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14
Q

Active transport occurs where (in the body) typically?

A

kidneys, liver, nervous system

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15
Q

Does facilitated diffusion require energy?

A

no - does not go against electrochemical gradient

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16
Q

Absorption from GI is favoured when drug is in its … form?

A

unionised - more lipophilic

17
Q

What are the drug properties influencing transfer across cell membranes?

A 
small or big molecules
acidic or basic
water or lipid solubility
extent of protein binding
existence of active transport system
18
Q

Re. drug distribution, drug is first delivered where?

A

heart, liver, kidney, brain and other well-perfused organs

19
Q

Factors that affect drug distribution…

A 
blood flow
barriers (eg. BBB, intestine, placenta)
protein binding (carrier protein)
20
Q

What is biotransformation?

A

metabolism of drug

21
Q

T or F - All drugs undergo one or more metabolic conversions

A

false - most do but some drugs get excreted unchanged

22
Q

Major site of drug metabolism?

A

liver

23
Q

Where are other drug metabolism enzymes found (apart from liver)?

A

kidney
lung
plasma
GI epithelium

24
Q

In order to facilitate elimination, what needs to happen to a lipophilic compound? where?

A

It needs to be converted to a more HYDROPHILIC one - liver

25
Q

What is the first-pass effect?

A

Extensive metabolism of drugs by GI mucosa and liver before they reach systemic circulation

26
Q

Define bioavailability… what is it influenced by?

A

fraction of drug dose administered orally that gets into the systemic circulation
influenced by:
- amount of absorption
- metabolism of drug in gut wall or liver before systemic circulation (1st pass metabolism)

27
Q

Re. drug metabolism reactions/biotransformation, what role do phase I & phase II have?

A

phase I - makes compound more reactive

phase II - increases water-solubility

28
Q

Phase I reactions can involve …?

A 
oxidation
reduction
hydrolysis
hydration
ie. addition of: -OH, -COOH, -NH2, -SH
often involves monooxygenase system with P450 plating key role
29
Q

Phase II reactions can involve…?

A

conjugation of an endogenous hydrophilic compound
glucuronidation (addition of glucuronic acid) - MOST IMPORTANT physiologically
glucosidation
sulfation
methylation
acetylation

30
Q

Principal organ of excretion? role?

A

kidney -> removes water-soluble material

31
Q

After the liver, what is the next most important organ of elimination?

A

liver -> eliminates metabolised drugs in bile

32
Q

What are the other organs involved in excretion?

A 
sweat glands
mammary glands
intestinal tract
salivary glands
skin
lungs
33
Q

When is biliary excretion a major route for drugs?

A

drugs that have a molecular weight > 300 and high degree of polarity

34
Q

A bit about bile…

A
  • produced by liver, stored in gall bladder except horse & rat (don’t have gall bladder)
  • pH 5.0 - 7.5 (species dependent)
  • active transport of drugs & metabolites into bile
  • secreted in faeces & may be subject to enterohepatic circulation & degradation by intestinal microflora

ASC306 (13 decks)

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