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Pharmacology > Absorption and Distribution > Flashcards

Absorption and Distribution Flashcards

1
Q

What is pharmacokinetics?

A

ADME. what the body does to the drug

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2
Q

does ADME occur simultaneously or in isolation

A

These processes happen in isolation, but the summation of these is the pharmacokinetic profile of the drug:

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3
Q

what does absorption depend on?

A

administration route

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4
Q

what 2 factors does distribution depend on?

A

-how lipid-soluble the drug molecule is (to pass through membranes)
-how the drug binds to blood plasma proteins (albumin). If drug binds to blood proteins → doesn’t really have biological efficacy.

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5
Q

what does elimination involve?

A

excretion into urine and/or by inactivation by liver enzymes.

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6
Q

PD factors

A

differing physiological responses to the same drug conc

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7
Q

PK factors

A

differing drug conc at the target area.

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8
Q

ED50

A

effective dose in 50% people

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9
Q

TD50

A

toxic dose in 50% of people

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10
Q

LD50

A

lethal dose in 50% of people

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11
Q

Margin of safety

A

= ED50 -TD50

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12
Q

Therapeutic Index

A

Therapeutic Index: ratio of median lethal or toxic dose to the median effective dose

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13
Q

define bioavailability

A

% of drug reaching the systemic circulation and available for bioactivity.

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14
Q

define bioequivalence

A

similarity between drugs/formulations. At the same conc., is one drug bioequivalent to another?

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15
Q

administration routes

A
  • Oral
  • Rectal
  • Inhalation
  • Topical
  • Parenteral (beyond the intestines): Intravenous, Intramuscular, Subcutaneous & Intraperitoneal
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16
Q

main site of absorption

A

small intestines

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17
Q

oral administration

& BUT

A

Needs to be:
- Soluble in gastric fluid otherwise won’t be absorbed
- Stable in gastric fluid otherwise will be broken down
- Enter the intestine and penetrate gut epithelium
- Enter the bloodstream

BUT, how much actually gets to the blood?

18
Q

Parenteral administration

& BUT

A

Beyond the intestines
- Fast acting
- Traverses fewer body compartments
- Delivers accurate dose

BUT, more likely to overdose, and once injected it cannot be recalled.

19
Q

Topical

A
  • Good for skin as easily absorbed
  • Stable controlled release
  • Minimises side effects
20
Q

min effective vs max tolerated

A

When a drug is administered, a peak is produced, which falls over time as its eliminated. Achieve highest level of drug within window of minimum effective concentration and maximum tolerated concentration for as long as possible.

21
Q

steady state

A

When drug concentration in the plasma is constant. Occurs within 3-5 half lives. Ideally, looking for steady state to fall within the therapeutic window.

22
Q

absorption vs distribution

A
  • Absorption: Passage of drug from site of administration → blood.
  • Distribution: Delivery of the drug from blood → tissue.
23
Q

what fraction of total body water does intracellular fluid make

A

2/3

24
Q

what fraction of total body water does extracellular fluid make

A

1/3

25
Q

what fraction of extracellular fluid does plasma fluid form

A

1/4

26
Q

what fraction of extracellular fluid does interstitial fluid form

A

3/4

27
Q

4 Ideal characteristics for maximal drug absorption

A
  • Low molecular size
  • Non-polar (made by amino acid side chains)
  • Charged (made by amino acid side chains)
  • High lipid solubility. BUT, this might mean its poorly dissolved in aqueous solutions.
28
Q

Ways to regulate the release of drugs

A
  • Dosage form = solution, capsule/tablet, cream
  • Excipients = added onto drugs to change properties (e.g., binders, disintegrants, diluents)
  • Delayed release (e.g., Enteric coating). The coating of oral tablets is broken down by the gut to ensure drug is delivered to the right place.
  • Sustained release (e.g., Matrix diffusion). Matrices can be implanted into body so drug is released over months.
29
Q

pKa

A

= acid dissociation constant = the pH value at which a species will accept or donate a proton i.e., in ionic form.
- Aspirin is a weak acid with a pKa of 3.5. At pH 3.5, 50% of it is in ionised form, and 50% is in unionised form.
- If the pH changes, these percentages also change.
- The unionised fraction is lipid soluble.

30
Q

7 factors determining the rate of permeability across lipid membranes

A

-permeability coefficient
-concentration difference
-Solubility of drug in the membrane (Lipophilicity is essential)
-Carrier-mediated transport through pH partition (Ionisation)
-Binding to plasma protein
-Blood flow at site of absorption
-Surface area in contact with the drug

31
Q

passive diffusion & what law it follows

A
  • Simplest way of transport.
  • High conc/pH → low conc/pH.
  • Variable rate.
  • Follows Ficks law of diffusion: rate of diffusion of a substance across unit area (such as a surface or membrane) is proportional to the concentration gradient.
32
Q

Carrier mediated transport/facilitated diffusion & what law it follows

A
  • Carrier proteins identify, bind and transport drugs across membranes.
  • Usually bind endogenous proteins.
  • Rate is much less variable than passive diffusion.
  • Follows Michaelis-Menten equation: used for enzyme kinetics.
33
Q

Active transport

A
  • Membrane channels actively move drug against conc. gradient
  • Low → high conc.
  • Requires energy in the form of ATP.
34
Q

Pinocytosis

A
  • Fluid endocytosis.
  • Extracellular fluid is taken up in a vesicle → invagination → budding of vesicle → which then releases the drug
  • Used for large and complex drugs (such as insulin being injected peritoneally).
35
Q

the compartment model

A

Within the body are interconnected compartments. The conc. of drug within a single compartment remains constant, however movement between compartments determines PK and PD of the drug (e.g., where and for how long a drug remains active in the body).

36
Q

factors affecting drug distribution (rate-2 and extent-5)

A

Affecting rate:
Membrane Permeability
Blood Perfusion

Affecting extent:
Plasma protein binding
Intracellular binding
pH differences
Lipid solubility
Available transport mechanisms.

37
Q

what plasma proteins do acidic drugs bind to

A

albumin

38
Q

what plasma proteins do basic drugs bind to

A

globulins (alpha and beta)

39
Q

what does binding of plasma proteins do to the drug?

A

makes drug inactive.

40
Q

Quantifying bioavailability

A
  • To quantify bioavailability, dose response curves are plotted.
  • One curve here gives dose response for IV and one for oral administration.
  • Area under curve (AUC) gives total bioavailability! Log conc/time.

Pharmacology (10 decks)

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