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PT3001: Introduction to Pharmacology > Pharmacokinetics I: Drug Absorption & Distribution > Flashcards

Pharmacokinetics I: Drug Absorption & Distribution Flashcards

1
Q

What is Pharmacokinetics?

A

What the body does to the drug and the interaction with the receptor

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2
Q

What are the FOUR stages in Pharmacokinetics?

A
  1. Absorption
  2. Distribution
  3. Metabolism
  4. Elimination
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3
Q

Do drug concentrations stay the same or change throughout each pharmacokinetic process?

A

Drug concentrations change

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4
Q

What is Drug Absorption?

A

The movement of a drug from its site of administration into the bloodstream

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5
Q

What is Bioavailability?

A

The fraction of drug administered that reaches the systemic circulation

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6
Q

What is the Bioavailability for intravascular drugs?

A

1
(100% absorption)

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7
Q

What is the Bioavailability for oral drugs?

A

Less than 1

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8
Q

What is the most common method of absorption for drugs?

A

Passive Diffusion

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9
Q

Which transporter absorbs Levodopa (L-DOPA) by active transport?

A

Amino Acid Transporter

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10
Q

Which transporter absorbs 5-Fluorouracil (5-FU) by active transport?

A

Pyrimidine Transporter

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11
Q

What type of drugs REDUCE gut motility and therefore drug absorption?

A

Muscarinic Receptor Antagonists

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12
Q

What is an example of a drug that INCREASES gut motility and therefore drug absorption?

A

Metoclopramide
(Pro-Kinetic)

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13
Q

How is drug absorption DECREASED with food intake?

A
  • DECREASED stomach emptying
  • INCREASED gut motility
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14
Q

How is drug absorption INCREASED with food intake?

A

INCREASED splanchnic blood flow

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15
Q

How does particle size affect drug absorption?

A

Large size = DECREASED absorption

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16
Q

Is drug administration by mouth fast or slow absorption?

A

Fast

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17
Q

Why is the absorption speed for drug administration by mouth what it is?

A

By-passes gastric pH and first-pass metabolism

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18
Q

What are TWO examples of drugs that are administered in the mouth?

A
  1. Glyceryl Trinitrate - for angina
  2. Benzodiazepines - epilepsy
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19
Q

What drugs are administered rectally in ulcerative colitis?

A

NSAIDs

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20
Q

What is Parenteral administration of a drug?

A

Drug given by a route that does not involve GI tract

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21
Q

What FOUR ways can drug molecules cross membranes?

A
  1. Passive Diffusion
  2. Facilitated Diffusion
  3. Active Transport
  4. Endocytosis
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22
Q

Are Polar or Non-Polar drugs more likely to cross a membrane by Passive Diffusion?

A

Non-Polar
(Lipophilic)

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23
Q

What TWO factors does Diffusion depend on?

A
  1. Concentration gradient
  2. Membrane surface area
24
Q

What are the TWO requirements need for Facilitated Diffusion of drug molecules across a membrane?

A
  1. Carrier Protein
  2. Ion Channel
25
Q

What is a clinical example of Facilitated Diffusion?

A

Fludeoxyglucose (FDG)
* Glucose analog with radio labelled fluorine
* Used in PET imaging as marker of cellular metabolism in tumours

26
Q

What are the FOUR requirements needed for Carrier-Mediated Transport?

A
  1. Specific Receptor
  2. Metabolic Energy (e.g. ATP)
  3. Against Conc. Gradient
  4. Saturation at High Conc.
27
Q

What are the FOUR main sites of Carrier-Mediated Transport?

A
  1. Renal Tubule
  2. Biliary Tract
  3. Blood Brain Barrier
  4. GI Tract
28
Q

What are the THREE forms of Endocytosis?

A
  1. Phagocytosis
  2. Pinocytosis
  3. Receptor-Mediated Endocytosis
29
Q

Which form of Endocytosis is the most selective?

A

Receptor-Mediated Endocytosis

30
Q

What TWO drugs are examples of drugs that cross the membrane by Endocytosis?

A
  1. Trastuzumab (Herceptin)
  2. Antibody-Drug Conjugates

(both used in cancer treatments)

31
Q

Do charged or uncharged drugs diffuse passively across the membrane?

A

Uncharged

32
Q

What THREE factors alter the ratio of unionised:ionised forms of a drug?

A
  1. pH of a body compartment
  2. Whether the drug is an acid or base
  3. pKa of the drug
33
Q

What is pKa?

A

A property of a chemical compound relating to its affinity for protons

E.g. Stong Acid = Weak Affinity
Strong Base = Strong Affinity

34
Q

What body compartment are ACIDIC drugs best absorbed in in terms of pH and pKa?

A

Unionised and better absorbed in compartments where pH < pKa

E.g. Stomach

35
Q

What is an example of an ACIDIC drug?

A

Aspirin (pKa = 3.5); Weak Acid

36
Q

What body compartment are BASIC drugs best absorbed in in terms of pH and pKa?

A

Unionised and better absorbed in compartments where pH > pKa

E.g. Small Intestine

37
Q

What is an example of an BASIC drug?

A

Pethidine (pKa = 8.6); Weak Base

38
Q

The ionisation state of a drug affects which TWO factors?

A
  1. Initial absorption into the blood stream
  2. Elimination from the blood
39
Q

How does ingestion of Sodium Bicarbonate affect Amphetamine (weak base) absorption?

A
  • INCREASES stomach pH
  • INCREASES amphetamine absorption
40
Q

How does ingestion of Vitamin C affect Amphetamine (weak base) absorption?

A
  • DECREASE urine pH
  • INCREASE weak base ionisation
  • DECREASE amphetamine absorption and enhances elimination
41
Q

What are the THREE main proteins involved in Drug-Plasma Protein Binding?

A
  1. Albumin
  2. β-Globulin
  3. Glycoprotein
42
Q

Which plasma protein(s) binds predominantly ACIDIC drugs?

A

Albumin

43
Q

Which plasma protein(s) binds mainly BASIC drugs?

A
  • β-Globulin
  • Glycoprotein
44
Q

TRUE OR FALSE:
Only unbound drugs can cross membranes and distribute into tissues?

A

True

45
Q

What happens when two drugs compete for the same plasma protein binding site?

A

INCREASE in free drug plasma conc. for both drugs

46
Q

What is Drug Distribution?

A

How a drug accesses extracellular space
i.e. organs, tissues, cells and sub-cellular comparments

47
Q

The Blood Brain Barrier restricts entry to which types of molecules?

A
  • Bacteria & Toxins
  • Large hydrophilic molecules
48
Q

The Blood Brain Barrier allows DIFFUSION of which types of molecules?

A
  • Gases e.g. O2 and CO2
  • Small hydrophobic molecules
  • Fat soluble molecules
49
Q

The Blood Brain Barrier allows ACTIVE TRANSPORT of which types of molecules?

A

Nutrients e.g. glucose, amino acids and vitamins

50
Q

What is the Volume of Distribution?

A

Theoretical volume necessary to contain drug at same concentration as that observed in plasma

51
Q

What is the equation for Volume of Distribution?

A
52
Q

What are the FIVE major fluid compartments in the body?

A
  1. Plasma (5%)
  2. Intracellular Fluid (35%)
  3. Fat (20%)
  4. Interstitial Fluid (16%)
  5. Transcellular Fluid (2%)
53
Q

What does a Vd value of < 3.5 L indicate?

A

Drug RETAINED in blood plasma

e.g. heparin

54
Q

What does a Vd value of < 13.5 L indicate?

A
  • Drug RESTRICTED to extracellular fluid
  • Drug does not enter cells easily

e.g. gentamycin

55
Q

What does a Vd value of > 13.5 L indicate?

A

Drug DISTRIBUTED through total body water or concentrated in certain tissues (most drugs)

56
Q

What is an example of a lipophilic drug with the potential to accumulate in body fat?

A

Thiopental

PT3001: Introduction to Pharmacology (18 decks)

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