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Jorge FCP > Pharmacokinetics and dynamics > Flashcards

Pharmacokinetics and dynamics Flashcards

1
Q

What does ADME mean?

A

absorption, distribution, metabolism, excretion

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2
Q

What do we use to measure drug conc and why?

A

Plasma - all drugs are in equilibrium in the plasma

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3
Q

What are Cmax and Tmax

A

Cmax = the peak level of action of a drug
Tmax = the time at which drug action is at its peak

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4
Q

Give an example of zero order drug kinetics

A

IV infusion - drug is instantly in plasma

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5
Q

Give examples of routes of administration that show first order kinetics

A

IM/SC/oral

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6
Q

What is Bioavailability (F)?

A

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

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7
Q

What factors affect bioavailability?

A

absorption
first-pass metabolism

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8
Q

What is the distribution phase of drug kinetics?

A

Distribution around the body occurs after drug reaches circulation
To leave plasma it must pass the plasma membrane

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9
Q

How do drugs leave the plasma

A

Only uncharged drugs can pass through membrane passively
Certain ionic compounds may go through as ion pair
Some pass through via active transport/carrier mediated transport

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10
Q

What are the features of compounds that can rapidly cross plasma membranes?

A

Low degree of ionisation
High lipid/water partition in non-ionised form
Relatively low molecular weight (small molecules)
biological affinity with transporters/facilitated diffusion

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11
Q

What is volume of distribution (Vd)

A

The volume into which a drug appears to be distributed with a concentration equal to that in plasma
A proportionality constant relating the blood/plasma concentration to the amount of drug in the body

Reversible process - drugs can leave and re-enter plasma

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12
Q

What affects the volume of distribution?

A

the drugs reversible affinity for tissue proteins vs plasma protein

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13
Q

What unit is Vd given in?

A

L/kg

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14
Q

What are the values of total body water and ECF?

A

Body water ~ 0.6L/kg
Body ECF ~ 0.1-0.3L/kg

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15
Q

Where does a drug with a Vd of 0.1-0.3L/kg accumulate?

A

most likely water soluble so mainly in ECF

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16
Q

Where does a drug with a high Vd accumulate?

A

other sites, not ECF e.g., fentanyl in fat

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17
Q

Give examples of barriers to drug distribution

A

Blood-brain barrier
Placenta - slows down, not complete barrier

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18
Q

Describe the blood-brain barrier as a barrier to distribution

A

Multiple tight junction, transporter and efflux pump
Control entrance and expulsion of molecules
Prevents uptake of most drugs
However, if diseased barrier can become leaky
Similar with the testes

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19
Q

Describe the placenta as a barrier to distribution

A

Trans-placental transfer of drug1: if a drug can be absorbed orally it likely to cross the placenta​
Ion trapping of drugs in fetus (particularly basic drugs)

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20
Q

What is the drug elimination rate?

A

The amount of parent drug eliminated from the body per unit time
Irreversible removal of parent drug (not metabolites)
Unit = mass or moles/t

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21
Q

What are the main routes of drug elimination?

A

Kidneys
Hepatobiliary system
Lungs

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22
Q

What are the secondary routes of drug eliminiation

A

milk
sweat

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23
Q

How are drugs metabolised?

A

Liver converts lipophilic drugs into hydrophilic form (inactive) => excreted

24
Q

What are CYP enzymes?

A

non-specific enzymes found in the liver that catabolise drugs
cause: oxidation, reduction, hydrolysis

25
Q

What is the significance of UGTs (uridine diphosphate glucuronyl transferases)?

A

Cats are deficient in it -> Limited ability to perform glucuronidation, paracetamol toxicity

26
Q

What factors affect the passive filtration of drugs in the glomerulus of the kidney?

A

GFR
Plasma binding proteins

27
Q

What factors affect the secretion of drugs from the proximal tubule of the kidney?

A

Affinity for transporters
Lipophilicity
Polarity

28
Q

What factors affect the re-absorption of drugs in the distal tubule of the kidney?

A

lipophilicity and polarity
Urine pH

29
Q

What is drug clearance (CL)?

A

A measure of the efficiency of the body to clear a drug
The volume of blood/plasma cleared of parent drug per unit time
Unit = L/h/kg

30
Q

What is the half life of a drug?

A

The time it takes for the plasma conc of a drug to halve
Always the same if the drug experiences first order kinetics

31
Q

What is polypharmacy?

A

When multiple drugs are taken simultaneously

32
Q

What are drug-drug interactions?

A

Altered pharmacologic response to one drug caused by the presence of a second drug

33
Q

What types of drug0drug interactions are there?

A

Pharmaceutical: interaction prior to administration
Pharmacokinetic: tissue/plasma levels of one drug altered by another one
Pharmacodynamic: action of one drug is altered by another one

34
Q

What are the possible outcomes of drug-drug interactions?

A

Summation
Potentiation
Synergism

35
Q

What is potentiation in drug-drug interactions?

A

When a drug on its own does not have an effect but may affect/be affected in combination with another drug

36
Q

What is summation in drug-drug interactions?

A

combined effect of two drugs produces a result that equals the sum of the individual effects of each agent

37
Q

What is synergism in drug-drug interactions?

A

Drug combinations produce a therapeutic or toxic effect greater than sum of each drug’s action

38
Q

Give an example of summation in drug-drug interactions

A

e.g. midazolam lowers the dose of propofol needed for anaesthesia

39
Q

Give an example of potentiation in drug-drug interaction

A

e.g. probenecid reduces penicillin excretion in urine and increases effectiveness of penicillin

40
Q

Give examples of synergism in drug-drug interactions

A

e.g. sulphonamide-trimethoprim (enhanced effects)
Toxicity: aminoglycosides and furosemide

41
Q

What are the pharmaceutical mechanisms on drug-drug interactions?

A

Physical
Chemical

42
Q

Describe physical drug-drug interactions

A

Incompatibility / interaction:
- Binding to plastic
- Insolubility in certain solutions

43
Q

Describe the chemical interaction of drugs

A

Stability of drugs is often pH dependent
Oxidation/reduction reactions
Complex formation eg chelation of drugs
Inactivated by certain vehicles

44
Q

What are the pharmacokinetic mechanisms of drug-drug interactions?

A

absorption
distribution
metabolism
excretion

45
Q

Give examples of absorption as a mechanism of drug-drug interactions

A

Change in gastric pH and bacterial flora
Chelation of drug in stomach
Altered gastric emptying: can increase or decrease absorption
Interference with intestinal efflux protein (P-glycoprotein)

46
Q

Give examples of distribution as a mechanism of drug-drug interactions

A

Competition plasma protein binding but this is not as clinically significant as originally thought
Some drugs reduce blood flow to organs, leading to a) reduced absorption from intra-muscular or sub-cutaneous administration or b) reduced clearance

47
Q

Give examples of metabolism as a mechanism of drug-drug interactions

A

Inhibition or induction of liver enzymes (CYP P450) leading to decreased or increase drug clearance.

48
Q

Give examples of excretion as mechanism for drug-drug interactions

A

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

49
Q

Give examples of drug that inhibit CYP P450 metabolism

A

Chloramphenicol
fluoroquinolones,
cimetidine
azole anti-fungals
calcium channel blocker,
omeprazole
propofol

50
Q

Give examples of drug that induce CYP P450 metabolism

A

Barbiturates (eg phenobartibal, primidone)
cyclosporin
carbamazepine

51
Q

What are the pharmacodynamic mechanisms of drug-drug interactions?

A

additive
synergistic
negation

52
Q

Describe additive interaction of drugs

A

can be beneficial or detrimental
Enables reduced doses to be administered
Can lead to increased toxicity

53
Q

Describe negation as a mechanism for drug-drug interactions

A

Opposing action leading to reduced effect

54
Q

What are adverse events (ADE)?

A

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

55
Q

What are the common ‘use-patterns’ associated with increased ADE?

A

Use of human-label drugs
Drugs with low therapeutic indices (more likely to have non-specific effects)
Inappropriate use
Lack of therapeutic goals
Multiple drugs
altered pharmacokinetics (young, old, lactating, pregnant etc.)

56
Q

what are the types of adverse events?

A

lack of expected efficacy
unexpected adverse event e.g., exaggerated normal response
Serious adverse event (life-threatening, permanent or prolonged) e.g., hypersensitivity - often idiosyncratic

Jorge FCP (59 decks)

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