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Principles 2018 > Pharmacology Part 3 > Flashcards

Pharmacology Part 3 Flashcards

1
Q

Define absorption

A

The process by which a drug enters the body from its site of administration and enters the circulation

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2
Q

Define distribution

A

The transport of the drug by the general circulation. Drugs often leave the blood and enter perfused tissues. Once within a tissue further, reversible, distribution dictated by a concentration gradient may occur by diffusion or carrier mediated transport

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3
Q

Define metabolism

A

The process by which tissue enzyme (principally in the liver) catalyse the chemical conversion of a frequently lipid soluble drug to an often less active and more polar form that is more readily excreted

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4
Q

Define excretion

A

The processes that remove the drug, or its metabolites from the body (principally the kidneys)

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5
Q

What are the linked processes of metabolism and excretion referred to as?

A

Elimination

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6
Q

Where does absorption of a drug occur

A

Stomach (limited)

Intestines (most)

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7
Q

Where does the drug move to after the liver?

A

Vascular compartment

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8
Q

Where does the drug move to following the vascular compartment?

A

Interstitial water or kidneys

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9
Q

Which physiochemical factors control drug absorption?

A
  1. Solubility
  2. Chemical Stability
  3. Lipid to water partition coefficient
  4. degree of ionisation
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10
Q

Describe drug solubility?

A

Drug must dissolve (dissolution) in an aqueous environment in order to be absorbed

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11
Q

Describe chemical stability of a drug?

A
  • some dugs are destroyed by acid in the stomach, or enzymes in the Gi tract
  • in a few instances a compound is modified within the gut to release the active drug
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12
Q

Describe the lipid to water partition coefficient in drug absorption?

A

the partition coefficient is the ratio of the drug concentration in the membrane and concentration in water at equilibrium

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13
Q

Describe the degree of ionisation of a drug?

A

Many drugs exist as weak acids or weak bases in ionised and unionised forms.

Only unionised forms can readily diffuse across the lipid bilayer

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14
Q

What does degree of ionisation depend upon?

A

pKa of the drug and local pH

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15
Q

What is pKa?

A

pH at which 50% of the drug is ionised and 50% is unionised

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16
Q

How can pKa be calculated?

A

Henderson-hasselbalch

17
Q

Where are drugs as bases absorbed?

A

Small intestine

18
Q

Where are acidic drugs absorbed?

A

Dacilitated by the pH of the stomach lumen

19
Q

Where does the majority of absorption occur?

A

In the small intestine (even for weak acids)

20
Q

What is the role of pH in absorption?

A

Weak acids and weak bases are well absorbed, strong acids (pKa < 3) and strong bases (pKa > 10) are poorly absorbed

acidic drugs become less ionised in an acid environment; basic drugs become less ionised in a basic environment

21
Q

What is gastrointestinal motility?

A

The rate of stomach emptying and movement through the intestines

22
Q

What modifies GI motility?

A

Drugs, disease, food

23
Q

What factors affect GI absorption?

A

GI motility
pH at absorption site
Blood flow (increased by food)
Tables manufacture (the time it takes to release)
Physiochemical interactions (modified by calcium rich foods)
Presence of transporters in the membrane of epithelial cells

24
Q

What is oral availability?

A

fraction of drug that reaches the systemic circulation after oral ingestion

25
Q

What is systemic availability?

A

fraction that reaches the systemic circulation after absorption

26
Q

How can PO drugs avoid first pass metabolism?

A

once absorbed, can be inactivated by enzymes in the gut wall and liver (first-pass or presystemic metabolism) before reaching the systemic circulation and body tissues in general

27
Q

What are the common routes of drug administration?

A 
Oral
Inhalational
Buccal/sublingual
Transdermal/subcutaenous
IV
Rectal 
Intramuscluar
28
Q

What compartments can drugs be distributed to?

A 
Plasma water
Interstitial water
fat
Intracellular water
transcellular water
29
Q

Which drugs can move from plasma water to interstitial water?

A

Ionised and unionised drugs that are not bound to protein

30
Q

Which drugs can move between

  • fat and interstitial water
  • intwstitial and intercellular water
  • intracellular and transcellular
A

Only unionised drugs

31
Q

Wha tis the apparent volume in which a drug is dissolved?

A

Volume of distribution (Vd)

32
Q

What does the Vd of an IV administered drug equate to?

A

Dose/Plasma concentration

33
Q

What does Vd of <10 L imply?

A

Drug is retained din vascular compartment

34
Q

What does Vd between 10 and 30L suggest?

A

restricted to extracellular water

35
Q

What does Vd >30 L suggest?

A

Distributed throughout total body water, maybe accumulation?

Principles 2018 (34 decks)

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