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Transition block > Pharmacology > Flashcards

Pharmacology Flashcards

1
Q

minimum effective concentration- what?

A

To achieve an effect a drug must have a minimum effective concentration in the plasma

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2
Q

what is the calculation of therapeutic window?

A

TR= MTC (maximum tolerated concentration)/ MEC (minimum effective concentration)

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3
Q

is a small or large therapeutic window safer in a drug?

A

A large therapeutic window is safer in a drug

-this means theres a large gap between the minimum effective concentration (MEC) and maximum tolerated concentration (MTC)
-the smaller the gap the more likely the body will not be able to tolerate a drug

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4
Q

examples of drugs with a large therapeutic window?

A

-Penicillins
-Benzodiazepines

larger therapeutic window= safer

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5
Q

examples of drugs with a small therapeutic window?

A

-Digoxin
-Warfarin

smaller therapeutic window= more unsafe

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6
Q

what is the quantal dose response relationship?

A

Quantal dose response relationship:
-plots the fraction of the population that responds to a given dose of drug against the drug dose
-the response measured is quantal (present or not present) instead of graded like change in bp

note: i think it basically is finding out what dose of drug has an effect on the average population???

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7
Q

explain what could be found in drugs that produce responses in 50% of the population?

A

-Median effective dose (ED50)
-Median toxic dose (TD50)
-Median lethal dose (TD50)

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8
Q

what are pharmacodynamics?

A

drug A modifies the effect of drug B without altering concentration in tissue fluid

dynamics= drug= duo/ dynamic between the duo

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9
Q

what are pharmacokinetics?

A

Drug concentration over time

Not easy to predict + Involves absorption, distribution, metabolism + excretion

kineTIC= clock ticks= drug conc over time

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10
Q

what can affect absorption? (phamacokinetics)

A

-drugs that increase/ decrease the rate of stomach emptying
-specific drugs that cause problems with normal bacteria for gut absorption

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11
Q

examples of drugs that increase/ decrease stomach emptying- affecting absorption in pharmacokinetics

A

Metoclopramide- increases stomach emptying, this can increase absorption (drugs are absorbed in enterocytes in intestine so faster if they leave stomach)

Atropine- decreases stomach emptying and so decreases absorption

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12
Q

what antibiotic reduces absorption + efficacy of COC?

A

rifampicin
-due to destroying the gut bacteria

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13
Q

what is volume distribution?

A

the theoretical volume occupied by a drug compared to plasma concentration

VD= amount of drug/ plasma concentration

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14
Q

what type of drugs cause a low volume distribution?

A

Drugs that are highly pound to plasma protein (do not get distributed into fat tissue)
-Large, charged drugs

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15
Q

what type of drugs cause a large volume distribution?

A

Drugs that are highly distributed into fat tissue compartments (small+ lipophillic)

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16
Q

what occurs to volume distribution in prgnancy?

A

Volume distribution increases:
-increase in GFR causes more proteins to be excreted
-less proteins for drugs to bind to
-increase in fat stores
-leads to higher distribution of drugs into fat tissue compartments (higher volume distribution)

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17
Q

what is half life?

A

time required to reduce the amount of drug in the body to 1/2

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18
Q

what is zero order elimination vs first order elimination?

A

zero order elimination:
-rate of elimination is constant
-depends on time not concentration of drug ingested

first order elimination: (more common)
-the rate of elimination is directly proportional to drug concentration
-can take 4 to 5 half lives to reach steady state

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19
Q

how does the bioavailability vary for IV or PO formulations?

A

IV= 100% bioavailability
PO= <100% bioavaialbility

bioavailability= fraction of drug avaialble to systemic circulation in an unchanged form

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20
Q

what is the first pass effect?

A

-refers to the pre systemic metabolism or elimination of a drug reducing bioavailability

pill> intestinal epithelium (enterocyte) > liver (hepatocyte) then either metabolism in hepatocyte or bile excretion (either way its bioavailability will be reduced due to going through bowel and liver)

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21
Q

what may change distribution of a drug?

A

drugs bound to plasma protein may be displaced by a second drug increasing their free concentration (would be able to move into fatty compartments increasing volume distibution)

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22
Q

what are the phases of drug metabolism?

A

Phase I- P450 oxidation, reduction and hydrolysis

Phase II- conjugation (sulfation, methylation, acetylation, glucuronidation)

23
Q

what part of pharmacokinetics particularly affects elderly?

A

Metabolism (especially phase II)

24
Q

what can effect phase I of metabolism?

A

P450 hepatic inducers and inhibitors

25
Q

role of P450?

A

P450 is an enzyme that breaks down drugs in the body- allowing them to be metabolised

26
Q

effect of P450 inducers?

A

P450 inducers break down more drug (enhance metabolism) and decrease efficacy of drugs

27
Q

example of a drug that is commonly affected by P450 enzyme inducers/ inhibitors?

A

Warfarin

28
Q

examples of P450 inducers?

A

CRAP GPS induces my rage= inducers= metabolise + clear drug faster= decrease efficacy of drug (e.g. WARFARIN)

Carbamazepine
Rifampicin
Alcohol
Phenytoin

Griseofulvin
Phenylbarbital
Sulfynureas (gliclazide)

29
Q

examples of P450 inhibitors?

A

These drugs INHIBIT P450 and so stop the metabolism of the drug, increasing toxicity in the body= potentiates effects

-Sodium Valproate
-Omeprazole
-Fluoxetine (SSRIs)
-Erythromycin (macroliders)
-Ketoconazole
-Isoniazid (TB medication)
-Sulfonimides
-Chloramphenicol
-Amiodarone
-Quinidine
-Grape fruit juice

30
Q

what effect would clarithromycin have if combined with warfarin?

A

Clarythromycin is a P450 inhibitor
-this would mean Warfarin wouldnt be metabolised as fast so would be potentiated

more bleeding!!

31
Q

what is elmination/ clearance?

A

volume of the body cleared of a drug over a unit of time

clearance= rate of elimination/ plasma concentration

clearance= volume distribution x elimination constant

32
Q

what determines time of steady state being achieved?

A

half life

33
Q

what determines the magnitude of steady state?

A

clearance and dose

34
Q

what could cause excessive dosage and/or decreased clearance?

A

-normal variation
-genetic enzyme deficiency
-renal failure
-liver failure
-old age
-very young age
-P450 enzyme inhibition

35
Q

what would cause too low of a dosage or increased clearance?

A

-poor absorption
-high first pass metabolism (passing through gut to be absorbed and then passing through liver to be metabolised)
-genetic hypermetabolism
-enzyme P450 induction
-non compliance

36
Q

what is Vmax and Km

A

Vmax= reaction rate when enzyme is fully saturated

Km= half of Vmax

37
Q

what occurs to Vmax and Km in competitive enzyme inhibition?

A

Vmax the same
Km is higher

38
Q

what occurs to Vmax and Km in non competitive inhibition?

A

Vmax decreases
Km remains the same

39
Q

what part of pharmacokinetics is altered in severe liver disease?

A

impaired drug metabolism if liver disease is severe

resulted from:
decreased liver blood flow + decreased enzyme metabolism capacity

40
Q

what is an example of a highly protein bound drug with a low TR?

A

phenytoin

41
Q

what is there a reduced production of the liver in liver disease (not p450 related) and how does this affect drugs

A

Reduced synthesis of plasma proteins (hypoproteinaemia)
-causes increased toxicity of highly protein bound drugs with a low TR (e.g. phenytoin)
-as there will be less proteins and so higher amount of phenytoin volume distribution

Reduced synthesis of clotting factors
-enhanced sensitivity to anticoagulants (warfarin)

42
Q

what drugs can worsen ascites in liver disease?

A

NSAIDs

43
Q

what can worse hepatic encephalopathy?

A

all sedatives

44
Q

where are drugs excreted?

A

mainly the kidneys

45
Q

what does renal excretion of drugs do to half life?

A

renally excreted drugs have a longer half life
-so may need a loading dose for rapid effect

46
Q

why does dosage of renally excreted drugs have to change with increase in age?

A

renal function declines with age

if a drug is eliminated prodominantly by kidneys it will accumulate and the maintenance dose must be reduced

47
Q

how is dosing adjusted?

A

Total daily maintenance dose can be reduced by:
-Reducing the size of individual dose (at unaltered interval)
OR
-Increasing the interval between doses (at unaltered individual dose)

48
Q

what makes elderly more vulnerable to adverse effects of drugs?

A

due to:
-impaired renal elimination
-increase sensitivity of target organs to drugs (e.g. brain, kidney)
-polypharmicy

49
Q

drugs to watch out for in elderly?

A

-digoxin
-antihypertensives
-CNS depressant drugs
-Warfarin
-NSAIDs

50
Q

what effect does digoxin have on elderly?

A

-increased risk of toxicity because of diuretic induced hypokalaemia and renal impairement

51
Q

what effect do antihypertensives have on elderly?

A

increase risk of falls due to baroreceptor functions

52
Q

what effect do CNS depressants have on elderly

A

increased sensitivity of the brain due to inhibitory effects and reduced elimination

53
Q

what effects do NSAIDs have on elderly?

A

increased risk of adverse effects of renal function and gastro toxicity

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