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Pharmacology I > 4. Pharmacokinetics: Transport mechanism of drugs, absorption, distribution > Flashcards

4. Pharmacokinetics: Transport mechanism of drugs, absorption, distribution Flashcards

1
Q

Pharmacokinetics

A

What the body does to the drug

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2
Q

Give the types of transcellular transport

A
  • Diffusion
  • Filtration
  • Facilitated diffusion
  • Active transport
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3
Q

Filtration

A

Bulk flow of solvent & solute through pores in the membrane

  • Concentration gradient affects the rate
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4
Q

Intracellular transport

A

Across gaps between endothelial & epithelial cells

  • Filtration
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5
Q

Degree of ionisation of a weak acid/base is determined by…

A
  • The pK of the drug
  • pH of its environment
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6
Q

When pK of a drug = pH of surroundings

A

50% ionisation occurs

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7
Q

Lower pK = stronger acid; Higher pK =

A

Stronger base

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8
Q

Rate of passage accross a semipermeable membrane is dependent on…

A
  • Pressure
  • Concentrations
  • Temperature
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9
Q

Permeability accross a semipermeable membrane is dependent on…

A
  • Solute size
  • Solubility properties
  • Chemistry
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10
Q

Drug absorption

A

Movement of drug into the bloodstream

  • Usually done via mucous surface
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11
Q

Reasons for ↓ absorption of drugs

A
  • Poor compound solubility
  • Chemical instability in stomach
  • Inability to permeate intestinal wall
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12
Q

Relation of small molecule absorption and blood flow

A
  • Absorption of small, very lipid-soluble molecules is “blood flow limited”
  • Higher polar molecules are “blood flow independent”
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13
Q

Bioavailability (F)

A

Fraction of drug that reaches the bloodstream unaltered

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14
Q

Absolute bioavailability

A

Measures the availability of the active drug in systemic circulation after non-IV administration

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15
Q

How is absolute bioavailability determined?

A

Pharmacokinetic study

  • Plasma drug conc. vs Time plot
  • Area under curve (AUC) for IV divided by that of non-IV administration
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16
Q

Bioavailability ≠

A

Bioequivalence

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17
Q

Relative bioavailability

A

Measure of the bioavailability of a drug when compared with another formulation of the same drug or delivered via a different route

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18
Q

Formula to calculate relative bioavailability

A
19
Q

List the factors affecting bioavailability

A
  • Poor absorption
  • Degradation
  • Intestinal motility
  • Disease
  • First pass effect
20
Q

First pass effect

A

Concentration of a drug is greatly reduced before it reaches the systemic circulation

21
Q

Topical/external administration sites

A
  • Skin
  • Mucous membrane
  • Nose
  • Mouth
  • Rectum
22
Q

Enteral administration sites

A
  • Oral
  • Rectal
  • Oro-/nasogastric
  • Intra-ruminal
23
Q

Parenteral administration sites

A
  • IV
  • SC
  • IM
24
Q

What is key for controlling the duration of drugs effect?

A

Rate of dissolution of tablets

  • If not readily dissolved, may be released more gradually over time with longer duration of action
25
Q

Distribution

A

Reversible transfer of drug from one location to another

  • Blood leaves bloodstream → EC fluids + Tissues
26
Q

Distribution is dependent on…

A
  • Permeability bewtween tissues
  • Blood flow
  • Perfusion rate
  • Ability of drug to bind plasma proteins & tissue
27
Q

For intracellular action drug must be…

A

Lipid soluble

28
Q

Volume of distribution (VD)

A

The volume of total body fluid into which drug “appears” to distribute

  • Quantifies the extent of distribution
29
Q

Volume of distribution is determined by…

A

Administrating a known dose of drug IV & measuring initial plasma conc.

  • Expressed in units of mass/volume
30
Q

Binding of plasma proteins

A
  • Only free drug diffuses through capillary walls
  • Extensive binding retards rate at which drug reaches its site of action
  • May prolong the duration of action
  • Generally reversible
31
Q

Drug redistribution

A
  • Relative distribution of drug changes with time
  • Usually highly lipophilic drugs that initially enter tissues with high blood-flow
  • Quickly redistribute to tissues with lower blood flow
32
Q

Blood brain barrier

A
  • Ionised/polar drugs distribute poorly to CNS + chemotherapeutic agents & toxic compounds
  • → Must pass through endothelial cells
33
Q

Placental barrier

A

Lipid-soluble drugs cross more easily than polar drugs

34
Q

Most drugs are absorbed by…

A

Small intestine

35
Q

Rate of dissolution is described by the…

A

Noyes-Whitney equation

36
Q

List the factors that may alter absorption from the GI tract

A
  • Gastric emptying time → Intestinal motility
  • GI blood flow
  • Stomach acid → Inactivating enzymes
  • Interactions with food & other drugs
37
Q

Absorption of small, very lipid-soluble molecules is…

A
  • “Blood flow limited”
  • Higher polar molecules are “blood flow independent”
38
Q

Distribution

A

Reversible transfer of drug from one location to another

  • Where drug leaves bloodstream & enters EC fluids & tissue
39
Q

Distribution is dependent on…

A
  • Permeability between tissues
  • Blood flow
  • Perfusion rate
  • The ability of a drug to bind plasma proteins & tissue
40
Q

For intracellular action, a drug must be…

A

Lipid soluble

41
Q

Volume of distribution (VD)

A

The volume of total body fluid into which drug “appears” to distribute

  • Quantifies the extent of distribution
42
Q

How is the volume of distribution determined?

A
  1. By administrating a known dose of drug IV (mass)
  2. Measuring initial plasma conc (mass/volume)
43
Q

Binding of plasma proteins

A

Generally reversible

  • The only free drug diffuses through capillary walls
  • Extensive binding retards rate at which drug reaches its site of action & may prolong duration of action.

Pharmacology I (19 decks)

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