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Medsci 204 > ADME > Flashcards

ADME Flashcards

1
Q

Passive diffusion

A

Most important mechanism
Applies to non-polar drugs
Conc gradient is the driving force
No energy required

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2
Q

Facilitated diffusion

A

Appears to depend on a oscillating carrier protein
Depends on the conc gard
No energy required
Sugars/amino acids

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3
Q

Active Transport

A 
Can proceed against a conc grad
requires energy
can become saturated
allows accumulation of specific compounds
removes waste product
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4
Q

Endocytosis

A

internalisation of large molecule by cell

mainly for drugs with a molecular weight higher than 1000

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5
Q

Drug absorption

A

The passage or a drug form the site of administration into the general circulation

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6
Q

Rate of absorption

A

how rapidly does the drug get from its site of administration to the general circulation?

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7
Q

Extent of absorption

A

how much of the administered does enters the general circulation

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8
Q

What is bioavailability

A

F - the area under the concentration time curve

the patients exposure to the drug

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9
Q

What is the minimum therapeutic level?

A

The level above which a drug needs to reach in order to produce a response

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10
Q

What are the enteral routes of drug administration?

A

per Ossa
Sublingual
Rectal

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11
Q

What are the parenteral routes of drug administration

A 
Intravenous
Sub cut
Intradermal
IM
lungs
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12
Q

What is the rate and extent of IV administration

A

Immediate absorption

100% aborption

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13
Q

What is the rate and extent of oral administration

A

Rate is gradual

extent is incomplete

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14
Q

What are the advantages of IV administration?

A

very rapid
precise control (100% F)
avoids problems of absorption
Good for irritating drugs

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15
Q

What are the disadvantages of IV?

A

skill required
Careful preparation of injected material (sterile)
no recall so is hazardous

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16
Q

What are the advantages of po administration?

A

Safe

convenient

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17
Q

What are the disadvantages of po administration?

A

slow

unpredictable with regard to rate, extent and reproducibility

18
Q

What are the factors influencing the bioavaliability of oral drugs

A 
Decomposition ir gastric acid
decompositon by gut enzymes
Degradation by gut microorganisms
Food in gut may alter absorption rate
Metabolism by gut wall enzymes
Metabolism by liver enzymes
19
Q

What is the rate limiting step of oral drugs?

A

The gastric emptying determines how quickly it is let into the small intestine to be absorbed.

Intestinal motility and interactions with food are also important

20
Q

What are the sites of drug metabolism?

A 
Liver
GI bacteria and proteases
Intestinal wall enzymes
Plasma (esterases)
Specialised tissue
21
Q

What is a prodrug?

A

A drug that has it’s activity promoted by metabolism

22
Q

What is an example of a drug that produces toxic metabolites when metabolised?

A

Paracetamol

23
Q

What is an example of a drug that has no change in activity when metabolised?

A

Valium (diazepam)

24
Q

What is phase 1 of a drug metabolism reaction?

A

The point is to make the drug more susceptible to phase 2 reactions

Oxidation
Reduction
Hydrolysis

25
Q

What is phase 2 of a drug metabolism reaction?

A

The point is to make the molecule more polar so that it’s an ideal substrates for active transport and excretion

Glucuronide
Sulphate
Amino acids GSH
Acetlyation.methylation

26
Q

What is the most important reaction for phase 1 metabolism of drugs?

A

Oxidation

27
Q

What happens during oxidation?

A 
The most important class of enzymes are the cytochrome P450 dependent mixed function oxidase system located in the smooth ER.
Requires oxygen, NADPH and cytochrome P450 reductase
28
Q

Describe the metabolism of Phenytoin

A

Phase 1 - hydroxylated to become slightly more soluble in water and inactive
Phase 2 - Becomes very soluble in water and highly lipophillic after conjungation by UDP transferase
compound is removed from liver and then 90% of it is excreted in urine

29
Q

What is the effect of age on drug metabolism?

A

It decreases it

30
Q

Which group has a higher metabolism and so requires a higher maintenance dose

A

Neonates

31
Q

Why do smokers have a higher metabolism?

A

Because there is a compound in cigarettes that can induce synthesis of metabolizing proteins in the liver

32
Q

How is drug metabolism inducted?

A

Enzyme synthesis is initiated wihtin 24h of exposure but the effect decreases over 1-3 weeks.

Cigarette smoking
BBQ meat
Cruciferous veges
High protein diet
Insecticides
PCBs
Barbituates
Pheytoin
Rifampcin
St johns wort
33
Q

How is drug metabolism inhibited?

A

rapid onset within 1 day
Exaggerated response with a risk of toxicity(no breakdown of drug)

Reversible inhinibtors
Cimetidine
Ketoconazole
quinolones
HIV protease inhibitors
Grapefruit juice

Heavy metals
Lead
Cadium
Mercury

34
Q

What is the outcome of the standard does of most drugs in a patient population?

A

20% will have no response
20% will get adverse effects
50-60% will get some therapeutic benefit

35
Q

What is excretion?

A

The process whereby compounds are removed from the body to the external environment

36
Q

What are the sites of drug excretion?

A

Kidney

Biliary excretion - important for drugs with a Mw >400 and ionized

Lungs

37
Q

What are the three main mechanisms of excretion by the kidney?

A
  1. Glomerluar filtration of the unbound drug (130ml/min)
  2. Active secretion of both free and protein bound drug by transporters. (Anions or cations)
  3. Filtrate 100fold concenrated in tubules for a favourable conc grad for reabsorption by passive diffusion (lipid soluble will pass back into body)
38
Q

What are the factors influencing renal drug excretion?

A

Gender (males higher)
Age (decreases with age)
Pregnancy (increases)
Disease

39
Q

How can you alter the renal excretion of drugs?

A

Competitive inhibition of tubular secretion (there is a second drug that has a higher affinity so decreases the excretion of the first drug)
e.g. penicillin decreased by probenecid

Influence of pH (sodium bicarbonate > increased excretion by stopping the reabsorption by ionising weak acids)(Ammonium chloride > increased excretion of amphetamines etc)

Urinary flow rate (dilutes drug conc in tubule > decreased conc grad > increased excretion)

40
Q

The effect of urinary flow rate on drug clearance is……?

A

Linear

41
Q

If someone overdoses on amphetamine what can you give them?

A

Ammonium cholride as this will increase the excretion of the drug from teh kidney

Medsci 204 (6 decks)

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