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PCL201 > Lec 17: drug interactions > Flashcards

Lec 17: drug interactions Flashcards

1
Q

what is the polypharmacy problem?

A

when ppl take a lot of drugs at sam etime, higher chance of drug drug ints

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2
Q

what types of drugs are there?

A

therapeutics, nontherapeutics, supplements, nhps, enviro chems

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3
Q

what are the three ways to categorize drug interactions?

A

pharmacodynamic (drug action, what drug does to body) and pl (what body does to drug) and unintentional vs intentional

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4
Q

what are each of the types of drug ints?

A

can be pd, pk, duplicative, direct or indirect

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5
Q

what are the types of pharmacodynamic drug interactions? which have a greater vs lesser effect?

A

dups, adds, syns (greater), antag (lesser)

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6
Q

what are duplications drug ints? additive? synergistic?

A

duplications (greater): same drug in two dif products (ie tylenol and neocitran both are acetaminphen)

additive (greater): both with same action mech and cause drastic effects (propanolol, timolol)

synergistic effects (greater): super additive, where 1+1&raquo_space;2: drugs have the same effect (ethanol and diazepam)

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7
Q

example of pd interaction? what do they do>

A

opioids (morphine, codeine, fentanyl) bind and activate mu opioid receptors

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8
Q

what are antagonistic drug ints? example?

A

when one drug prevents the binding and action of the other drug. fentanyl and naloxone

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9
Q

antagonistic vs partial agonistic effect?

A

antag: one blocks the other
partial ag: also competes for the recep, so does reduce effect of the full ag

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10
Q

what is an inverse agonist?

A

antagonistic to the full agonist – has the opp effect of the agonist (favours inactive. ie: doesnt just block, but favours this)

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11
Q

how do drug ints occur through non comp binding?

A

theyre not binding at the same site, but binding at dif site on same receptor, or at dif spots in the body

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12
Q

what are the pharmacodynamic drug ints?

A

combined toxicities
duplications (tylenol and neocitran –> acetominophen)
additive (propanolol and metroprolol –> both lower bp)
synergistic (ethanol and diazepam –> CNS depressants)
antagonistic (morphine and naloxone –> upioid receptors)

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13
Q

when are pd drug ints increased?

A

you activate the same recep by two or more drugs binding at same site
drug binds to recep, conf change allowing another drug to bind on same receptor (pos allo mod)
2+ drugs have same clinical effect, different mech

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14
Q

when are pd drug ints decreased?

A

agonist and antagonist given together

negative allosteric modulation

2+ drugs with opposing clinical effects

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15
Q

what are the pharmacokinestic drug interactions?

A

abs
dist
bitrans
excretion

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16
Q

what interactions affect absorption ?

A

physiochem
gi motility
changes in bacterial flora
gastric ph
mucosal damage
drug transporters

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17
Q

what are physiochemical interactions?

A

things that make drugs stick together

ion exchange binding
chelation dissolution
gastric ph

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18
Q

what is ion exchange binding? example?

A

drugs with opp charges attracted to eo

heparin (-) and protamine sulfate (+)
when bound, heparin is neutralized, lose anticoag effect

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19
Q

what is chelation? example?

A

molecules of chelating agent form bonds iwth metal ion

lead and edta
iron and deferoxamine

you want to give a drug to get rid of the high metal levels so that the drug u want isnt chelated

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20
Q

what is dissolution? example?

A

drug dissolves in material that isnt absorbed

fat sol vitamines dissolving in mineral oil, dont actually get absorbed, pass through

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21
Q

how do gastic ph changes affect drug absorption? example?

A

ph alterations effect how well some drugs get absorbed

ph raised by antacids, recep antagonists, proton pump inhibs

22
Q

when do drugs get ionized (acidic vs basic)

A

when pka > ph, protonation

for acids: when pka > ph, acid is protonated, not ionized

for bases: when pka > ph, base is protonated, ionized

23
Q

henderson hassel bach equation:

A

pka - ph = log [prot]/[deprot]

24
Q

when are acidic drugs in their uncharged form? basic drugs?

A

acids are uncharged when pka > ph
based are uncharged when pka < ph

remember only uncharged drugs can pass the membranes !!

25
Q

how do changes in bacterial flora affect drug absorption?

A

if antibiotics kill natural bacteria in gut, biotrans of certain drugs can get reduced (like dogoxin)

26
Q

how does gastro intestinal motility affect drug absorption?

A

if u speed up or slow down motility it can affect the rate and extent of absorption of drugs

27
Q

how do cathartics affect gi motility

A

increase motility, and could increase rate of absorption, but slow extent of absorption

28
Q

how do opioids affect gi motility

A

opioids decrease motility, decrease rate of emptying and rate of abs, increase extent of abs bc its in body for longer

29
Q

how does mucosal damage impact drug absorption. example?

A

drugs impact the barrier functions of gi tract

nsaids: damage mucosa, easier for drugs to enter

30
Q

how do drug transporters impact absorption

A

depedning on whether drug is a substrate, inhibitor, activator of certain transporter, can impact what does/doesnt get transported

31
Q

which are the uptake tranporters

A

slcs:
oats
oatps
octs
octns

32
Q

which are the efflux transporters

A

abcs:
mdr
mrp
bcrp

33
Q

how do non drugs affect drug absorption

A

can inhibit transporters and thereby decrease absorption and or excretion

34
Q

explain relationship between fexofenadine and grapefruit juice

A

grapefruit juice: inhibits uptake oatp1a2
reduces amount of fexo (antihistamine) that gets into blood steam
cant carry out its function

35
Q

explain relationshio between digoxin and propafenone

A

propafenone inhibits pgp efflux transporter mdr1 , so helps keep digoxin in body for longer, greater absorption, greater serum conc

36
Q

what kinds of drug interactions affect distribution

A

being displaced from plasma proteins
displaced from tissue bindig sites
alterations in blood flow
alterations in local tissue barriers
interactions at drug transporters

37
Q

explain the protein binding of warfrin

A

its an anticoag and slows down blood clotting, and most is bound to albumin

38
Q

what happens to warfarin binding when phenytoin is present

A

phenytoin (antiseizure) has higher albumin affinity, too much free warfarin, more bleeding (too much anticoag effect)

39
Q

explain relationship between loperaminde and quinidine

A

loperamine = antidiareah drug is an opioid so slows metabolism, but gets kicked out by pgp so doesnt cross bbb

but quinidine inhibits pgp, so loperamide gets into brain and you get high

40
Q

what happens to desmethyl loperamide when injected with or without mdr1 inhibitors? what does this show?

A

when blocked, loperamide enters brain
when unblocked, drug doesnt enter brain

41
Q

what happens when you inhibit placental bcrp?

A

placenta has pgb and bcrp (efflux), nicardipine inhibits efflux, keeps drug in the moms placenta longer.

42
Q

how does drug metabolism get affected by interactions??

A

inhibit drug metabolising enzymes (hours, days)
induce drug metabolising enzymes (weeks) - need to make new proteins

43
Q

how can you inhibit drug metabolism?

A

terfendine and erythromycin
cyp3a4 inhbition by ketoconazole, erythromycine, grapefruit juice

44
Q

how can you induce drug metabolism? examples?

A

rifampin and carbamazepine induce cyp3a4, metabolise contraceptive med (and estrogen, progestin) too fast

phermobarbital induced cyp2c9 which metabolises warfarin

45
Q

how does excretion get impacted by drug interactions?

A

ph can get altered, making some drugs more ionized so you dont reabsorb them

inhibiting drug transporters
inducing drug transporters

46
Q

explain relationship between probenecid and peniccilin

A

penicillin is a subtrate of oats trasnporter
oat helps penecillin get into pt to be excreted
probenecid blocks oat and prevents excretion of penecillin

47
Q

relationship between cyclosporine and st johns wort> what happened? what does this demostrate?

A

st johns wort induced cyp3a4, ppgp.
more met, more efflux, leads to less cyclosproin

didnt have enough immunosuppressant (cyclo) therefore hearts were rejected

48
Q

how can you investigate drug interactions?

A

in silico
in vitro
in vivo

49
Q

why is knowledge of drug ints important

A

lets u understand plasma conc
predict plasma drug conc
avoid adverse interactions
make beneficial interactions

50
Q

why might you create drug ints

A

to increase plasma levels
to reverse resistance
to penetrate bbb or maternal fetal barrier
to prevent tox
to treat overdoses

51
Q

overall impacts of pk drug interactions

A

abs, dist, biotrans, excretion

52
Q

how to avoid drug ints

A

PCL201 (19 decks)

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