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Principles of Therapy > Theme 3 - Pharmacokinetics > Flashcards

Theme 3 - Pharmacokinetics Flashcards

1
Q

Explain what is meant by the term pharmacokinetics

A

The study of movement of drugs into, within, and out of body i.e. WHAT THE BODY DOES TO THE DRUG

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2
Q

What are the 3 different routes of administration of a drug?

A

Enteral, parenteral, other

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3
Q

What are the 3 enteral routes of administration?

A

Oral ingestion, rectal, sub-lingual (under tongue)

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4
Q

What are the 3 parenteral routes of administration?

A

Intravenous, intramuscular, subcutaneous

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5
Q

What are 2 other routes of administration?

A

topical and inhalation

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6
Q

What is meant by the term “absorption of a drug”

A

process of crossing biological barriers into the blood

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7
Q

What is the pKa of a drug?

A

The pH at which 50% of a drug exists in its ionised hydrophilic form (in equilibrium with its unionised form)

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8
Q

Explain the theoretical importance of plasma protein binding of drugs

A

Protein binding prevents drugs being rapidly excreted/metabolised, allows for a slow supply of the drug

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9
Q

What effect will displacement of the drug from plasma proteins cause?

A

Unbound drugs diffuse across membranes and get metabolised and excreted, so if drugs are displaced then free drug concentration in the plasma will increase leading to overactivity of the displaced drug.

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10
Q

Explain the blood-brain barrier and how it functions with regards to drug permeability

A

Permeability of capillaries of brain lower than that of body because there are no gaps found in capillary walls, hydrophilic drugs cannot pass BBB, drugs with high lipid-water distribution coefficient can cross BBB (CNS drugs)

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11
Q

Describe drug distribution across the placenta

A

The foetal enzyme systems that handle drug metabolism and excretion mechanisms are poorly developed

Any lipophilic drug that crosses the placenta leaves the foetus by redistribution to maternal circulation

Mass of the foetal brain in relation to other body parts is large, so capacity for distribution to the brain is larger

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12
Q

What is meant by the term “first-pass effect”

A

Portion of drug metabolised immediately after absorption, causes drugs to be inactive when taken orally

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13
Q

What is enterohepatic circulation of a drug?

A

Absorbed drug re-enter digestive tract via gall

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14
Q

What is Phase I metabolism?

A

Metabolic modification such as oxidation, reduction and hydrolysis
Electron rich groups added/made available (for conjugation in phase II)
Introduces or exposes functional group

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15
Q

What is Phase II metabolism?

A

Synthetic or conjugation reactions of glucuronic acid, glycine, glutamate, sulphate and acetate.
Addition of hydrophilic group to drug for excretion by kidneys/bile
Drugs with electron rich groups do not have to undergo phase I metabolism

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16
Q

What are the 3 types of Phase I metabolism?

A

Microsomal (in SER) metabolism, Cytosolic metabolism, Mitochondrial metabolism

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17
Q

What is the cytochrome P450 system?

A

non- specific and can add molecular oxygen to a large variety of lipophilic drugs

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18
Q

Give 2 examples of Microsomal metabolism

A
  • Barbital undergoes aliphatic hydroxylation to form inactive hydroxy derivative
  • Phenacetin undergoes aromatic hydroxylation to form Chlorpromazine which ungergoes S-Oxidation
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19
Q

What are the 2 types of Cytosolic metabolism?

A

Hydrolysis and oxidation

20
Q

Give an example of oxidation

A

Ethanol undergoes alcohol dehydrogenase to form acetaldehyde

21
Q

Give an example of hydrolysis

A

Acetylcholine becomes choline + acetate

22
Q

Give an example of Mitochondrial metabolism

A

catecholamines become deaminated products (MAO)

23
Q

What are the 5 conjugation reactions?

A

Glucuronide formation, Sulphate formation, Methylation, Acetylation, other (detoxification)

24
Q

What is conjugation?

A

Drugs become water-soluble (for excretion)

25
Q

What are the factors that influence the excretion of drugs?

A

Polarity of drug
pH of urine
Drug form (bound/unbound to proteins)
Kidney function

26
Q

What does excretion take place via (6)

A 
Kidneys
Gall
Faeces
Sweat
Breast milk
Lungs (gas and vapours)
27
Q

What must the polarity of a drug be to be excreted?

A

polar (hydrophilic)

28
Q

In what pH of urine are weak bases excreted?

A

low pH (acidic)

29
Q

In what pH of urine are weak acids excreted?

A

high pH (alkaline)

30
Q

How can urine be changed to facilitate excretion of drugs?

A

The pH can be changed

31
Q

In which form (bound/unbound to protein) are drugs filtered into urine?

A

unbound

32
Q

What are the 2 ways drugs can enter urine?

A

filtration in the glomeruli

specific secretion via the cells of the kidney tubuli

33
Q

Where do almost all drugs that are administered to a lactating mother enter?

A

breast milk

34
Q

Do weak bases/acids enter breast milk?

A

weak bases (breast milk pH is 6)

35
Q

Define the term “half-life” (t1⁄2)

A

The time that is required to excrete 50% of the absorbed dose

36
Q

What is the clinical importance of the half-life of a drug?

A

To determine the time interval between the dosages

37
Q

When is the steady state of a drug achieved in the blood?

A

after approximately 4,5 x t1⁄2 period

38
Q

What is first-order kinetics of a drug?

A

When a constant fraction of the drug is eliminated per unit time, the excretion of the drug follows exponential kinetics

39
Q

What is zero-order kinetics of a drug?

A

When a constant mass of the drug is eliminated per unit time. AKA saturable metabolism

40
Q

What is the clinical importance of first and zero order kinetics?

A

It is important in cases of drug overdose, when the half-life is increased due to saturation of the excretion processes

41
Q

How does first-order kinetics influence the half-life of a drug?

A

it remains constant

42
Q

How does zero-order kinetics influence the half-life of a drug?

A

it varies

43
Q

What is a loading dose?

A

An initial higher dose of a drug that may be given at the beginning of a course of treatment

44
Q

Explain the term “volume of distribution” (Vd) of a drug

A

A constant that displays the relationship between the total amount of drug in the body and the concentration in the plasma. The higher the Vd, the more likely that the drug is found in the tissues of the body. The smaller the Vd, the more likely that the drug is confined to the circulatory system.
Vd = total amount of drug in the body/concentration of the drug in the plasma

45
Q

Define the term “clearance” (Cl) of a drug

A

The relationship between plasma concentration of a drug and the amount of drug that is eliminated per unit time

46
Q

What is the clinical importance of clearance?

A

Important to accurately calculate maintenance dosages in an individual patient.

47
Q

Define the term “bioavailability”

A

The fraction of unchanged drug reaching the systemic circulation following administration by any route.

Principles of Therapy (10 decks)

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