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Sem 5 > Pharmacology 1: Safe prescribing and pharmacokinetics intro > Flashcards

Pharmacology 1: Safe prescribing and pharmacokinetics intro Flashcards

1
Q

Requirements for a safe prescription?

A 
Right drug
dose
route
site frequency
to right patient
AND must consider allergies, contraindications, interactions and adverse effects.
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2
Q

what is a black triangle drug?

A 
1 being intensively monitored
generally 1 which has been: newly released
changed indications
changed formulations
combination product
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3
Q

what is a serious reaction?

A

results in or prolongs hospitilisation

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4
Q

what SEs may occur with metformin use?

A

diarrhoea, abdominal pain, nausea, vomiting, lactic acidosis- as too much glucose for O2 in tissues so revert to anaerobic metabolism

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5
Q

describe a model which can be used for error causation in prescribing?

A

Reason’s model of error causation:
4 primary components: latent conditions- organisational processes and management decisions
error producing conditions- environ, team, indiv, task factors
active failures- slips, lapses, mistakes (errors) and violation
defences- protect against hazards, mitigate consequences of failure

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6
Q

examples of defences in prescribing errors?

A

prescription checking by nurses and pharmacists
electronic reviews- e.g. warnings displayed before certain prescriptions allowed to be processed
senior reviews

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7
Q

what is the difference between slips and lapses, and mistakes?

A

slips and lapses occur with loss of concentration, and maybe memory, meaning that the action isn’t carried out as intended. Mistakes occur when there is poor knowledge or rules are confused, so the action is carried out as intended, but the outcome is not as expected.

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8
Q

What is verapamil and when is it used?

A

L-type Ca2+ blocker, used in HF and arrhythmias (class IV anti-arrhythmic)
Acts at SAN and AVN in arrhythmia
Has -ve inotropic and chronotropic effects, + causes dilatation of peripheral arterioles and CAs in HF to reduce workload of heart.

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9
Q

common side effect of statins?

A

muscle pains

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10
Q

4 components to pharmacokinetics?

A

ADME: absorption, distribution, metabolism and excretion

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11
Q

factors determining OB?

A

formulation of drug (long or short acting?)
route of administration
age
lipid-soluble>H20-soluble if given with food
vomiting/malabsorption
GI/hepatic disorders, transporter and enzyme avaialability 1st pass metabolism

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12
Q

major factors affecting drug distribution in the body?

A

lipophilicity/hydrophobicity
degree to which it binds to plasma protein
degree to which it binds to tissue proteins
mass or volume of tissue and density of binding sites within that tissue

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13
Q

what 3 main factors are used as the basis as to whether a drug should be included in a formulary (list of formulae for compounded medicines)

A

cost
efficacy
safety

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14
Q

what is efficacy?

A

ability of a drug to activate a receptor and produce a response

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15
Q

what is potency?

A

how good a drug is at producing a response

measured by EC50= effective conc of a drug giving 50% of maximal response

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16
Q

things to remember when prescribing drugs?

A 
PRESCRIBER
patient details
reactions- drugs (allergies?) and interactions
sign drug chart
contraindiciations
route
IV fluids check
blood clotting
emetics- induce vomiting to get rid of unwanted substances before absorbed
relief- pain, have they enough?
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17
Q

why must patient be monitored if on MXT?

A

immune system suppressor, so must do FBC to check for BM suppression

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18
Q

what does 1st pass effect mean for drug dosages when prescribing?

A

a drug which is heavily metabolised by the liver would have to be give at a relatively high dosage in order to achieve its therapeutic effect

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19
Q

define 1st pass metabolism

A

any metabolism of a drug that occurs prior to its entry into the systemic circulation

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20
Q

where can 1st pass metabolism occur?

A

gut lumen e.g. gastric acid, proteolytic enzymes e.g. insulin, benzylpenicillin
gut wall e.g. P-glycoprotien efflux pumps e.g. ciclosporin
liver e.g. propranolol and morphine

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21
Q

what is drug distribution?

A

ability of a drug to dissolve in the body

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22
Q

when are changes in protein binding of a drug important?

A

if high protein binding
low Vd
narrow therapeutic ratio

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23
Q

what factors affect protein binding of a drug?

A

hypoalbuminaemia e.g. liver failure, nephrotic syndrome
renal failure
pregnancy
displacement by other drugs

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24
Q

why is high-dose aspirin avoided in patients on warfarin?

A

increases risk of bleeding as warfarin= class I drug, and aspirin= class II, so aspirin displaces warfarin from protein binding sites, so its free concentration is increased, as class II drugs are given at a dose greater than the number of available albumin binding sites.

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25
Q

how is the half life of a drug related to its volume of distribution and its clearance?

A

t1/2 is directly proportional to volume of distribution

inversely proportional to clearance

26
Q

factors affecting tissue distribution?

A 
specific receptor sites in tissues
regional blood flow
lipid solubility
AT
disease states e.g. HF, malnourishment
drug interactions
27
Q

why are non-ionised molecules more readily absorbed?

A

more lipid-soluble

28
Q

Other than IV, SC and IM, how can a drug be given to avoid the portal circulation?

A

sub-lingual

rectal

29
Q

function of conjugation in drug metabolism?

A

make drugs water-soluble for elimination

30
Q

what reactions do enzymes in phase I drug metabolism catalyse?

A 
oxidation
reduction
hydrolysis
dealkylation
existing functional groups on drug molecules are modified
31
Q

what can drugs be conjugated with during phase II of drug metabolism?

A

glutathione
glucuronide
sulphate
N-acetyl

32
Q

name given to drugs which are metabolised to their active forms in the body?

A

pro-drugs

33
Q

example of a drug which is active when given, but is also metabolised to produce active metabolites?

A

codeine to morphine

34
Q

enzymes involved in phase I drug metabolism?

A

cytochrome (CYP) p450

35
Q

influences on phase I drug metabolism?

A 
enzyme-inducing and inhibiting drugs
age
liver disease
hepatic b.flow
alcohol and cigarette consumption
genetic polymorphisms
36
Q

where are CYP450 isoenzymes found?

A

mainly liver
gut
lungs

37
Q

CYP450 3A is involved in the metabolism of what?

A

benzodiazepines e.g. diazepam. Used in anxiety states and epilepsy.
Ca2+ channel blockers
most statins
cyclosporin
HIV protease inhibitors e.g. ritonavir, saquinavir
most non-sedating anti-histamines

38
Q

inhibitors of CYP 3A?

A

grapefruit juice
cimetidine
macrolides
anti-fungals e.g. fluconazole

39
Q

CYP 3A inducers?

A

carbamazepine
St John’s Wort- herbal remedy for depression
rifampicin- inhibits RNA polymerase, targets protein synthesis, e.g. for TB- OCP may not work!
ritonavir- drug used for HIV, alongside HAART

40
Q

importance of drug reaction between cimetidine (H2 antagonsit) and warfarin?

A

cimetidine= CYP 3A inhibitor, so warfarin not metabolised- plasma conc increases- increase PTT, increased bleeding risk.

41
Q

what 3 processes determine the renal excretion of drugs?

A

glomerular filtration
passive tubular reabsorption
active tubular secretion

42
Q

example of drugs actively secreted at PCT?

A

penicillin

43
Q

what is passive tubular reabsorption in the kidney affected by? Bearing this in mind, why would you want to give alkaline diuresis to a patient who has overdosed on aspirin?

A

urine flow rate and pH
aspirin= weak acid, alkaline diuresis will make urine alkaline, putting aspirin into its ionised form which cannot be reabsorbed and so will be excreted.

44
Q

why might we want to monitor a drug?

A

narrow therapeutic index
0 order kinetics- t1/2 cannot be defined ( remember that most drugs when given at a very high dose will exhibit 0 order kinetics)
drug-drug interactions
long t1/2
known toxic effect
monitoring therapeutic effect e.g. BP and glucose

45
Q

when is a steady state achieved in drug administration?

A

when dosage rate (rate entering systemic circulation)= rate of elimination
during repeated drug administration, a new steady state is reached in 3-5 half lives

46
Q

what might dosing regimen be dependent on?

A

t1/2
drug interactions
age of patient
renal function

47
Q

what can be used as a measure of affinity?

A

Kd= dissociation constant= conc of ligand required to occupy 50% of available receptors.

48
Q

term given to describe how well a drug produces the maximum response?

A

intrinsic activity

49
Q

what do full agonists have in common, and what might differ between them?

A

same intrinsic activity as elicit maximum response
but may have different efficacies, as receptor activation may occur for different proportions of binding events between the 2 drugs.

50
Q

what 2 key factors determine OB?

A

absorption

1st pass metabolism

51
Q

how does Vd affect initial drug concentrations?

A

high if small Vd

loading dose required to fill up Vd when small initial concentration

52
Q

define clearance

A

the volume of plasma that is completely cleared of the drug per unit time

53
Q

examples of prodrugs?

A

tamoxifen
losartan- AngII blocker
codeine

54
Q

why is genetic variability, an important part of pharmacogenomics, an important factor affecting drug metabolism?

A

certain populations exhibit polymorphisms or mutations in 1 or more enzymes of drug metabolism, so the rate of some of these reactions is changed, and some eliminated altogether. e.g. metabolism of isoniazid slowed in some populations as reduced synthesis of an enzyme= slow acetylators (N-acetyltransferase enzyme).
also as free isoniazid= inhibitor of CYP 450, makes slow acetylators more prone to adverse drug reactions.

55
Q

why is safe prescribing even harder with increasing numbers of elderly patients?

A

co-morbidities
polypharmacy
increased risk of SEs

56
Q

what is the yellow card scheme?

A

used in reporting: all suspected reactions from black triangle drugs and unlicensed herbal preparations, established products and vaccines, and all paediatric reactions.

57
Q

why does plasma drug concentration decrease more slowly in the elimination phase?

A

reservoir of drug in the tissues that can diffuse back into the blood to replace the drug which is being eliminated

58
Q

organs other than the liver which can contribute to systemic drug metabolism?

A

GI tract, kidneys, skin, lungs

59
Q

how does rate of drug absorption affect peak plasma concentration and duration of drug action?

A

faster rate= higher peak plasma concentration (Cmax) as all drug absorbed before significant elimination can take place
slower rate= longer duration of action as drug still being absorbed during the elimination phase

60
Q

how can the BB barrier be bypassed in order for a drug to access the CNS if it can’t pass through the barrier?

A

intrathecal infusion- drug delivered directly into CSF

Sem 5 (35 decks)

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