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LF261 - Neuropharmacology > Pharmacokinetics -> lecture 1 > Flashcards

Pharmacokinetics -> lecture 1 Flashcards

1
Q

What is the most important clinical aim when developing drugs?

A
  • To achieve a long enough effective drug conc at action site to cause an action.
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2
Q

What is the therapeutic range?

A
  • Range = concentrations where the drug causes an effect, above min effective conc but below toxic conc.
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3
Q

Do we drug to stay in therapeutic range for a long or short time?

A

Long as possible as it means the drug conc is high enough to cause an effective action for longer.

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4
Q

How to calculate the therapeutic index?

A

Maximum non-toxic dose/Minimum effective dose.

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5
Q

What is LD50/ED50?

A

LD50 - lethal dose for 50% of people.
ED50 - effective dose for 50% of people. (smaller = higher potency)

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6
Q

What is the path of drugs through the body?

A

A - Adsorption
D- Distribution
M- Metabolism
E- Elimination

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7
Q

What is bioavailability?

A

How much of a drug dose is unchanged when reaching action site.

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8
Q

How can we create 100% bioavailability?

A

Make all drug reach site, mainly via IV drug (direct into bloodstream).

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9
Q

How does an orally ingested drug move from GI tract to Circulation?

A

Passive diffusion

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10
Q

How to measure rate of passive diffusion?

A

Fick’s law:
rate = (permeability * SA * Δ concentration)/membrane thickness

Permeability = only controllable factor.

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11
Q

Does the chemical state of drugs affect absorption?

A

Most are weak acids/bases. (lower rates of ionisation)
Uncharged/Unionised drugs = better absorption

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12
Q

What are the alternative methods to absorption?

A
  • Active transport (taken up by transporters etc)
  • Pinocytosis (vesicles capture, pinch + release drug)
    Experimental = - Solvent drag (v lipid soluble drug = dissolve in solvent, carry drug through membrane)
    Theoretical = - Ion-pair absorption (high retention, polar drugs only - bind to non-polar counter ions)
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13
Q

What is the main place drugs are absorbed in the body?

A

Small intestine => large SA, highly vascularised, alkaline.

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14
Q

What are some secondary places of drug absorption?

A
  • Stomach => small SA, low blood flow, acidic.
  • Colon => possible metabolism by bacteria + slow-release?
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15
Q

What are the 3 things that affect drug absorption?

A
  • State
  • Gut Motility
  • Splanchnic blood flow.
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16
Q

How does a drugs physical state affect absorption?

A
  • Solution = most rapid move into action site.
  • Suspension = dissolution to solution
  • Tables = disintegrate, de-aggregate (into fine particles), dissolution into a solution.
17
Q

How does gut motility affect drug absorption?

A
  • Meal size + composition affects motility.
  • Ingestion of certain drugs.
  • Position of body.
18
Q

How does splanchnic blood flow affect absorption?

A
  • Dependent on concentration gradient btwn blood flow + GI organs.
19
Q

How are drugs distributed in blood?

A

Drugs enter plasma + bind to proteins.

20
Q

What proteins do drugs bind to in blood?

A
  • Weak acids = albumin.
  • Weak bases = glycoproteins.
21
Q

Is the binding saturation of a drug in blood linear or non-linear?

A

Non-linear relationship btwn dose + free drug conc.
i.e. There is a larger [free drug] in blood just from small increase in [drug].

22
Q

How are drugs distributed in tissues?

A

Depends on: solubility, binding affinity, size etc.
- Anaesthetics go into fat.
- Antidepressants go into extravascular tissue.

23
Q

How are drugs distributed in the brain?

A

Brain = protected by blood brain barrier.
- Lipid-soluble = passive diffusion.
- Water-soluble = via carriers.

24
Q

What is the blood brain barrier and how does it protect against drugs?

A

A layer of endothelial cells which contain a p-glycoprotein pump which is an efflux pump i.e. has an active drug outflow pump.

25
Q

What is the main organ in which orally-ingested drugs get metabolised before entering blood?

A

The liver

26
Q

How are drugs metabolised in the liver?

A
  • First pass metabolism -> i.e. reduces drug conc before reaching blood stream.
27
Q

What is meant by high first pass metabolism?

A

If drug almost completely metabolised = high first pass i.e. there is little left to enter blood stream.

28
Q

What are the 3 metabolic modes of action in the liver?

A
  • Converts drug to inactive metabolite.
  • Converts drug to active metabolite.
  • Drug isn’t changed + so is excreted.
29
Q

What are the 2 phases of metabolism in liver?

A

1:
- Change molecular structure via cytochrome P450 enzymes.
- Reduction, hydrolysis etc.

2:
- Conjugate via transferase enzymes
- Add ionised group, making more water soluble (easier excretion, lower activity).

30
Q

Do drugs have to undergo both phases of liver metabolism?

A

No, can undergo both in either order or just do one.

31
Q

How can we bypass high rates of first-pass metabolism ?

A

Change drug administration method:
- Inhalation -> direct to blood.
- Transdermal -> through skin to blood.
- Buccal/sub-lingual -> passive absorption into blood.
- Rectal -> upper (veins = still first pass), middle = avoids.
- Injections:
-> sub-cutaneous = small vols but passive diff into blood.
-> Intramuscular = larger vols, long lasting in blood stream etc.

32
Q

What’s the main organ drugs are excreted by?

A
  • Mainly the kidneys
33
Q

What type of drugs are excreted?

A
  • Only unbound (not bound to plasma proteins etc).
34
Q

What can happen to highly lipid soluble drugs in the kidneys and what is the effect?

A

Possibly be re-absorbed into renal tubes.
This prolongs the drugs action.

35
Q

Can excretion be increased?

A

Yes, change the urine pH by adding bicarbonate/aspirin etc.

36
Q

What happens to un-metabolised drugs?

A

Are excreted unchanged which is dangerous.
Can cause possibly kidney damage particularly due to toxic drug accumulation levels.

37
Q

Are drugs excreted anywhere else in the body except for the kidneys?

A
  • In bile into intestine -> conjugates drug. Potential for reabsorption via enterohepatic circulation back into bloodstream after absorption in small intestine.
  • Saliva/sweat.
  • Breastmilk

LF261 - Neuropharmacology (3 decks)

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