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LEAH FCP > Pharmacokinetics & dynamics > Flashcards

Pharmacokinetics & dynamics Flashcards

1
Q

What do drugs from different routes all go to

A

Plasma

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2
Q

From where do we measure drug concentrations

A

plasma

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3
Q

Label the graph

A
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4
Q

What absorption routes follow zero order and which follow first order

A

IV infusion = zero order kinetics
IM/SC/oral = tend to follow first order kinetics

First order: the greater the concentration the greater the rate

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5
Q

Define bioavailability (F)

A

Measure of extent of absorption from administration site to measurement site (plasma)

fraction/percentage of administered dose that reaches plasma

Incorporates absorption and first-pass metabolism

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6
Q

What is the distribution phase of a drug

A

process of drug moving from bloodstream into tissues and fluids of the body

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7
Q

What kind of drugs can move across membranes?

A

Higher lipophilicity = greater membrane permeability

Only uncharged drugs can pass through membrane core

Certain ionic compounds may go through as ion pair or through ion channel

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8
Q

What role do transport mechanisms play in drug distribution?

A

Drugs may use active transport or carrier-mediated transport, which allows movement against concentration gradients but may saturate at high drug concentrations.

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9
Q

What factors influence drug distribution across membranes?

A

Lipophilicity

degree of ionization (low can cross)

molecular weight (<1000)

affinity for transporters.

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10
Q

Define volume of distribution (Vd)

A

volume into which drug appears to be distributed with
concentration equal to that in plasma

Vd is reversible process, however, together with drug clearance (irreversible) influences rate of drug elimination

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11
Q

What influences Vd?

A

magnitude of Vd for a drug is influenced by its reversible affinity for tissue proteins versus plasma protein

high affinity = high distribution

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12
Q

What does Vd indicate about a drug’s distribution?

A

It shows whether a drug is mainly confined to plasma, extracellular fluid, or distributed widely into tissues.

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13
Q

What is the typical Vd for drugs that are water-soluble and remain in extracellular fluid?

A

Between 0.1–0.3 L/kg, such as NSAIDs

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14
Q

What does a high Vd (e.g., 2 L/kg or more) indicate?

A

drug accumulates in tissues, such as fat or other compartments, as seen with general anesthetics like fentanyl.

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15
Q

Name 2 barriers to distribution

A

Blood-brain barrier

Placenta

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16
Q

How does the blood-brain barrier affect drug distribution?

A

It restricts most drug entry due to tight junctions, transporters, and efflux pumps

However, if diseased barrier can become leaky

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17
Q

How do drugs cross the placenta?

A

Most drugs that can be absorbed orally can cross the placenta, often through passive diffusion.

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18
Q

What is ion trapping in the context of the placenta?

A

It occurs when basic drugs accumulate on the fetal side due to differences in pH

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19
Q

What is drug elimination rate

A

amount of parent drug eliminated from body per unit time

Elimination rate is defined with respect to irreversible removal of parent drug and does not include metabolites

Units: Mass or Moles per time

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20
Q

What are the primary routes of drug elimination?

A

Kidneys, hepatobiliary system, and lungs (for volatile compounds).

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21
Q

What are the secondary routes of drug elimination?

A

milk, sweat

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22
Q

What are the 2 elimination processes that drugs can go through

A
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23
Q

Describe drug metabolism

A

Liver protects the body from drugs/xenobiotics

Lipophilic drugs will be transformed to become hydrophilic (polar), often inactive, and then be excreted.

The drug transformation may be a 2-phase reaction (but the phase I may be sufficient to inactive and excrete the drug)

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24
Q

What are the two phases of drug metabolism?

A

Phase I (catabolic reactions: oxidation, reduction, hydrolysis) and Phase II (anabolic reactions: conjugation).

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25
Q

What happens during Phase I metabolism?

A

The drug is chemically modified, often making it more reactive or preparing it for conjugation in Phase II.

26
Q

What is the role of CYP enzymes in drug metabolism?

A

They catalyze Phase I reactions, including oxidation, reduction, and hydrolysis, to modify drugs for further metabolism or excretion.

27
Q

What is the main conjugation reaction in Phase II metabolism?

A

Glucuronidation, where drugs are conjugated with glucuronic acid to form water-soluble metabolites.

28
Q

What is the outcome of drug metabolism?

A

The formation of water-soluble metabolites, which are usually inactive and ready for excretion.

29
Q

What is the role of CYP450 in drug metabolism

A

phase 1 oxidation

30
Q

Why do different animals react differently to the same drug?

A

Different animals have varying CYP enzyme profiles, leading to differences in drug metabolism.

31
Q

What does the term “non-specific” mean regarding CYP enzymes?

A

CYP enzymes can act on multiple substrates, not limited to a single specific compound.

32
Q

Which enzyme family is primarily responsible for glucuronidation?

A

Uridine Diphosphate Glucuronyl Transferases (UGTs).

33
Q

Why are cats prone to toxicity from drugs like paracetamol?

A

Cats have a deficiency in UGT enzymes, limiting their ability to perform glucuronidation.

34
Q

Where are glucuronide conjugates excreted?

A

In bile and urine

35
Q

What is the significance of glucuronidation in drug metabolism?

A

It transforms lipophilic drugs into hydrophilic forms, facilitating their elimination from the body.

36
Q

How are polar vs non-polar drugs excreted?

A
37
Q

What are the main processes of renal drug excretion?

A

Glomerular filtration (filters free drug), tubular secretion (actively transports drugs into tubules), and tubular reabsorption (lipophilic drugs may re-enter the bloodstream).

38
Q

How does urine pH influence drug excretion?

A

Alkaline urine enhances the excretion of weak acids, while acidic urine enhances the excretion of weak bases.

39
Q

What factors affect renal drug excretion?

A

Glomerular filtration rate (GFR), plasma protein binding, drug polarity, urine pH, and affinity for transport proteins.

40
Q

What is drug clearance

A

The volume of blood/plasma cleared of a drug per unit time, expressed as L/h/kg

41
Q

What is the half-life of a drug?

A

The time it takes for the plasma concentration of a drug to reduce by half.

42
Q

What factors affect half life?

A

Larger clearance = shorter half life
Higher volume of distribution = longer half life

43
Q

What is polypharmacy?

A

The concurrent use of multiple drugs, increasing the risk of drug interactions

44
Q

What are the three main types of drug-drug interactions?

A
45
Q

What is summation?

A
46
Q

What is potentiation?

A
47
Q

What is Synergism?

A
48
Q

What are pharmaceutical drug interactions?

A

Interactions that occur before drug administration, often due to physical or chemical incompatibilities

49
Q

What is an example of physical incompatibility in pharmaceutical interactions?

A

Binding of drugs to plastic containers or infusion sets (e.g., diazepam binding to plastic)

Insolubility: Certain drugs precipitate in solutions, such as amphotericin B in electrolyte solutions

50
Q

What are examples of chemical incompatibility in pharmaceutical interactions

A

Stability of drugs is often pH dependent e.g. penicillin G is inactivated by alkaline sulphonamide

Oxidation/reduction reactions e.g. tetracyclines are oxidised by
riboflavin

Complex formation eg chelation of drugs

Inactivated by certain vehicles eg Fluoroquinolones can be inactivated in calcium-containing solutions

51
Q

What are pharmacokinetic drug interactions?

A

Interactions where one drug alters the absorption, distribution, metabolism, or excretion of another drug

52
Q

How can absorption be affected in pharmacokinetic interactions?

A

Altered gastric pH (e.g., antacids reducing the absorption of acidic drugs).

Chelation in the stomach (e.g., calcium binding to tetracyclines).

Altered gastric emptying (increasing or decreasing absorption).

Interference with intestinal efflux proteins (e.g., P-glycoprotein inhibition).

53
Q

How do pharmacokinetic interactions affect drug distribution?

A

Competition for plasma protein binding sites (though clinically less significant).

Altered blood flow to organs (e.g., reduced organ perfusion affects distribution and clearance).

Interactions with tissue transport proteins.

54
Q

What are the two main ways metabolism is affected in pharmacokinetic interactions?

A

Enzyme induction: Increases drug metabolism, reducing plasma drug levels.
Examples: Barbiturates, carbamazepine.

Enzyme inhibition: Decreases drug metabolism, increasing plasma drug levels.
Examples: Fluoroquinolones, azole antifungals, grapefruit juice.

55
Q

How can excretion be altered in pharmacokinetic interactions?

A

Urinary pH will alter clearance of renally excreted drugs i.e. more alkaline will increase excretion of weak acids

56
Q

What are additive effects in pharmacodynamic interactions?

A

When the combined effect of two drugs equals the sum of their individual effects

Can be beneficial or detrimental

Enables reduced doses to be administered: e.g.
- Barbiturates & benzodiazepines for sedation
- Opioids and NSAIDs for analgesia

Can lead to increased toxicity e.g.
- NSAIDs & steroid: increased risk of GI ulceration
- NSAIDs & aminoglycosides: increased risk of nephrotoxicity

57
Q

What is synergism in pharmacodynamic interactions?

A

When the combined effect of two drugs is greater than the sum of their individual effects.

Example:
- Sulphonamide and trimethoprim (enhanced antibacterial effects).
- Aminoglycosides and furosemide (toxicity).

58
Q

What is negation in pharmacodynamic interactions?

A

When one drug opposes the action of another, reducing its effect.

Examples:
- Atipamezole reversing medetomidine.
- Naloxone reversing opioids

59
Q

Define adverse events

A

Unintended or noxious response to a drug that occurs within a reasonable time frame following administration

60
Q

What are some “use-patterns” associated with increased ADE

A

Use of human-label drugs (haven’t undergone same testing)

Drugs with low therapeutic indices (non-selective)

Inappropriate (trivial) use

Lack of therapeutic goals

Multiple drugs

Young, old, altered PK

61
Q

What are the different types of adverse events?

A

LEAH FCP (49 decks)

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