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Pharmacokinetics Flashcards

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1
Q

Define pharmacodynamics

A

Study of the drug effect and mechanisms of action

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2
Q

Define pharmacogenetics

A

The effect of genetic variability in the pharmacokinetics and pharmacodynamics of a drug on an individual

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3
Q

What are the main processes in drug therapy?

A

Pharmaceutical process - is the drug getting into the patient
Pharmacokinetic - is the drug reaching its site of action
Pharmacodynamic - is the drug producing the required pharmacological effect
Therapeutic process - is the pharmacological effect being translated into a therapeutic effect

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4
Q

What are the components of the pharmacokinetic process?

A

Absorption
Distribution
Metabolism
Elimination

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5
Q

What is bioavailability (F)?

A

The fraction of a dose that finds it way into a body compartment - usually the circulation

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6
Q

What is the bioavailability for an IV bonus?

A

100%

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7
Q

How is bioavailability calculated?

A

The area under the curve in a graph of plasma concentration against time

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8
Q

What factors can affect bioavailability?

A

Absorption

  • drug formulation
  • age
  • food - lipid soluble > water soluble
  • vomiting, malabsorption etc

First pass metabolism

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9
Q

Where can first pass metabolism occur?

A

Gut lumen - gastric acid, proteolytic enzymes, grapefruit juice
Gut wall - p-glycoprotein efflux pumps drugs out of the intestinal enterocytes back into the lumen
Liver

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10
Q

What is first pass metabolism?

A

Any metabolism occurring before the drug enters the systemic circulation

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11
Q

What are the two key factors affecting distribution?

A

Protein binding

Volume of distribution

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12
Q

Which proteins can drugs bind to?

A

Albumin (acidic drugs)
Globulins (hormones)
Lipoproteins (basic drugs)
Acid glycoproteins (basic drugs)

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13
Q

What factors can affect protein binding?

A

Hypoalbuminaemia
Pregnancy
Renal failure
Displacement by other drugs

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14
Q

How can volume of distribution be calculated?

A

Dose divided by [drug] at t0

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15
Q

What is the relationship between half life and volume of distribution?

A

Half life is proportional to Vd

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16
Q

What can tissue distribution be affected by?

A 
Specific receptor sites in tissues
Regional blood flow
Lipid solubility 
Active transport 
Disease states
Drug interaction
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17
Q

What is the aim of drug metabolism?

A

Normally so that drugs can be water-soluble and so eliminated rapidly from the body

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18
Q

What happens in phase 1 metabolism?

A

Oxidation and reduction

Uses CYP450 enzymes

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19
Q

What can affect CYP450 enzyme activity?

A 
Enzyme-inducing and inhibiting drugs
Age
Liver disease
Hepatic blood flow
Cigarettes
Alcohol
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20
Q

Where can CYP450 enzymes be found?

A

Liver
Gut
Lung

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21
Q

What are the main enzyme inducer drugs?

A

Phenytoin
Carbamazepine

Barbiturates
Rifampicin
Alcohol
Sulphonylureas

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22
Q

What are the main enzyme inhibiting drugs?

A

Omeprazole

Disulfiram
Erythromycin 
Vaporic acid
Isoniazid
Cimetidine
Ethanol (acute)
Sulphonamides
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23
Q

What are the different routes of elimination of drugs?

A 
Kidney
Lungs
Breast milk
Sweat
Tears
Genital secretions 
Bile
Saliva
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24
Q

What three processes determine renal excretion of drugs?

A

Glomerular filtration
Passive tubular reabsorption
Active tubular secretion

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25
Define clearance
Ability of the body to excrete a drug
26
Relationship between clearance and GFR?
Normally equal | If GFR decreases, so does clearance
27
What is the relationship between half life and clearance?
Half life is inversely proportional to clearance | As clearance increases, half life decreases
28
What are first order kinetics?
Rate of elimination is proportional to drug level. A constant fraction of drug is eliminated per unit of time. Half-life can be defined. Linear
29
What are zero order kinetics?
Where rate of elimination is constant and independent of drug concentration. Gives a straight line when linear
30
What does clearance/volume of distribution equal?
k - the elimination constant
31
How can half life be calculated?
(0.693 x Vd) / clearance
32
How do HRH factors affect clearance?
Heart - CVS system factors affect blood flow to the main organs of elimination Renal - factors affecting renal elimination Hepatic - factors affecting hepatic elimination
33
Why are zero order kinetics unpredictable?
Fixed rate of elimination per unit time Therefore, small dose changes can produce large increments of dose or lead to toxicity Cannot calculate a half life
34
When is drug monitoring required?
Zero order kinetics Long half life Narrow therapeutic window Risk of DDIs Known toxic effects eg bone marrow suppression Monitoring therapeutic effect eg BP, glucose
35
After how many half-lives is a steady state achieved?
4 to 5 | Irrespective of dose or frequency of administration
36
Define pharmacokinetics
Study of the movement of a drug through the body | What the body does to the drug
37
Give pharmacokinetic features of digoxin
Large Vd Excreted by kidneys Long half life
38
What does a loading dose allow?
Achieve a rapid therapeutic dose level - can skip forward a few days if there is a long half life
39
Antidote for digoxin?
Digifab
40
Symptoms of a digitoxic patient?
Bradycardia Xanthopsia (see yellow) Vomiting
41
Which pathway is most paracetamol metabolised by normally?
Glucaronide and sulphate pathways
42
Which is the bad pathway for paracetamol and why?
P450 oxidation | Produces NAPQI which is conjugated with glutathione to produce inactive metabolites
43
How is a paracetamol overdose treated?
Glutathione replacement - N-acetylcysteine
44
Equation to work out loading dose?
Loading dose = Vd x target drug concentration
45
Way does the slope of an elimination curve represent?
The elimination rate constant (k) | k = ratio of clearance to Vd
46
At what types of sites can drugs work?
``` Cell surface receptors Nuclear receptors Enzyme inhibitors Ion channel blockers Transport inhibitors Inhibitors of signal transduction proteins ```
47
Define affinity
The tendency of a drug to bind to a specific receptor type
48
Define efficacy
The ability of a drug to produce a response as a result of the receptor or receptors being occupied - describes the maximum effect of a drug
49
Define potency
Dose required to produce the desired biological response. | Describes the different doses of two drugs requires to exact the same effect
50
How is the therapeutic index calculated?
EC50 of adverse effect / EC50 of desired effect i.e. Toxic dose (TD50) / effective dose (ED50)
51
What is the therapeutic index (in words)
The range of doses that can effectively treat a condition while still remaining safe
52
What is the difference between time of onset of drugs that inhibit and drugs that induce CYP enzymes (like how long does it take for the effects of the DDIs to be seen?)
Inhibition of enzymes happens quickly (hours to days) | Induction of enzymes happens over days to weeks
53
How to calculate the loading dose?
Vd x CpSS (steady state plasma concentration)
54
Give some examples of DDIs
Agonism/antagonism at the same receptor Agonism/antagonism at different receptors Non-selective drugs Enhanced effect by other means eg digoxin toxicity enhanced by hypokalaemia caused by a loop diuretic
55
Example of agonism/antagonism at the same receptor? (DDI)
Opiate analgesics and naloxone | Beta blockers and beta 2 agonists
56
Example of agonism/antagonism at different receptors?
Amlodipine and bendroflumethiazide | Warfarin and aspirin
57
Give an example of a drug which is not selective which can lead to ADRs
Antidepressants - interact with many receptor subtypes - adrenergic - noradrenergic - serotoninergic - cholinergic
58
Which drugs commonly have DDIs?
``` Anticonvulsants Antibiotics Anticoagulants Antidepressants/antipsychotics Antiarrhythmics ```
59
Which foods can cause interactions and how?
Grapefruit juice - inhibit several CYP450 enzymes which reduces clearance of drugs Cranberry juice - inhibits CYP2C9
60
Which drugs should you not have grapefruit juice with?
Simvastatin | Amiodarone
61
Which drugs should you not have cranberry juice with?
Warfarin - enhances its anticoagulant effect
62
How can renal disease lead to adverse effects?
Reduced clearance | Disturbances of electrolytes may predispose to toxicity, especially potassium
63
How can hepatic disease affect drug activity?
Reduced clearance of hepatically metabolised drugs Reduced CYP450 enzymes Longer half-lives
64
What is the classic drug to be careful of in hepatic disease?
Opiates in cirrhosis - small doses can accumulate leading to coma
65
How can cardiac disease affect drug activity?
Excessive response to hypotensive agents Reduce organ perfusion -hepatic -renal
66
What factors increase the risk of ADRs?
Careless prescribing Polypharmacy Patients at extremes of age due altered PK profile and co-morbidities Multiple medical problems Drugs with narrow therapeutic index Drugs used near their minimum effective concentration - increased risk of treatment failure
67
What are the different severities of ADRs?
Major - permanent/life threatening Moderate - requires additional treatment Mild - trivial/unnoticeable
68
What are some patient causes of variability in drug response?
``` Body weight Age Gender Genetics Condition of health Placebo effect ```
69
What are some causes related to administration that can affect drug response?
``` Dose Formulation Route of administration Repeated administration of drugs -allergies -resistance -tolerance ```
70
What are some causes of variability in drug response due to drug interactions/kinetics
``` Chemical/physical GI absorption Protein binding/distribution Metabolism (stimulation/inhibition) Excretion Receptor (potentiation/antagonism) Changes in pH/electrolytes ```
71
Define specificity
Drug is limited to one receptor - the complementary drug and receptors Will not activate other receptors even at high concentrations
72
Define selectivity
The clinical effect the drug has and can be measured with specific therapeutic indices Increase the conc can cause it to bind to other receptors But has a greater affinity for one receptor
73
What are some pharmacokinetic-related DDIs which affect absorption?
- changes in gut motility eg opiates and atropine increase Cmax and Tmax - calcium salts bind to tetracyclines to reduce their absorption - cholestyramine binds to warfarin and digoxin to reduce their absorption
74
What are some pharmacokinetic-related DDIs which affect distribution?
Object drugs administered at a dose where there are more binding sites than molecules. Precipitant drugs administered so there are more molecules than binding sites so they displace object drugs Administering a precipitation drug can cause object drug levels to rise to toxic levels
75
What are some pharmacokinetic-related DDIs which affect metabolism?
Can affect the metabolism of themselves or other drugs by induction or inhibition of enzymes
76
What are some pharmacokinetic-related DDIs which affect excretion?
Can decrease the protein binding of another drug which accelerates its excretion. Can inhibit tubular secretion resulting in increased plasma levels eg NSAIDs can reduce tubular secretion
77
What are on target ADRs?
ADRs which are due to the exaggerated therapeutic effect of the drug eg due to increased dosing -drugs for hypertension can cause dizziness Often include effects on the same receptor type but found in different tissues
78
What are off target ADRs?
Involves interaction of other receptor subtypes secondarily to the one intended for the therapeutic effect Can occur with metabolites that can act as a toxin Also includes inappropriate immune responses

Pharmacology (23 decks)

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