Cyto P450 interactions

[NRAI2001]

For any category of drugs there is always a few "Inducers" and "Inhibitors" of Cyto P450.. I understand the concept of inducers and inhibitors but I am unsure of how I should approach memorizing/learning specific drugs and their effects on p450 and drug interactions..??

I know FA has a chart of inducers and inhibitors they feel are important... but how should we use this chart? I know some of the inducers listed on the chart lead to reductions in other drugs not listed on the chart (ie reductions in drugs that may not be considered as inducers in of themselves)..ie warfarin, diazepam, digioxin...etc are not listed but are often discussed when it comes to inducers and inhibitors??

I ve heard that this is a very high yield concept, so any help would be appreciated😀

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[njmedstudent87]

yes this is an absolute must to know

most of the drugs listed in that mnemonic will specifically mention cyp inhibition or activation when u individually study the drug but honeslty its just from repetition...you must know the notorious drugs like rifampin, macrolides, carbamazepine, phenytoin, grapefruit juice (which is only intestinal cyp 450). most of then the question will involve someone with a prolonged PT on warfarin and what was the reason....

 

[NRAI2001]

yes this is an absolute must to know

most of the drugs listed in that mnemonic will specifically mention cyp inhibition or activation when u individually study the drug but honeslty its just from repetition...you must know the notorious drugs like rifampin, macrolides, carbamazepine, phenytoin, grapefruit juice (which is only intestinal cyp 450). most of then the question will involve someone with a prolonged PT on warfarin and what was the reason....

Thats the thing... the list only lists the inducers themselves... but the inducers/inhibitors have effects on drugs not listed in either list (ie like you mentioned warfarin which is not on either list). Any advice on how to approach it??

Very confused🙁 Thanks😀

 

[njmedstudent87]

easy thing that helps,

carbamazepine, phenytoin, barbs and quinidine are all drugs that deal with action potentials...neuronal or cardiac...and they all induce

with exception of rifAMPin and griseofulvin (dont know how u'd remember that) the inhibitors are mainly antrimicrobials

 

[njmedstudent87]

don't know how to approach the specific issue ur referring to...i guess once you do so many questions which mention them once in a while it kind of gets imprinted into you...so memorize and practice i guess

pharm i hate because it is the most easily forgotten subject...i constantly have to revise it...everything else you can reason with...not pharm

 

[kryptik]

Thats the thing... the list only lists the inducers themselves... but the inducers/inhibitors have effects on drugs not listed in either list (ie like you mentioned warfarin which is not on either list). Any advice on how to approach it??

Very confused🙁 Thanks😀

A lot of drugs are metabolized by the liver P450 system eg warfarin, but only the inducers and inhibitors can speed up or slow down the system itself.

Basically if the stem describes a situation where the effects of a drug is greater than expected suspect an inhibitor, if less than expected suspect inducers, it will be impossible to learn every drug that is metabolized by the p450

Another way is describing a condition in which the drug of choice is one of the inducers or inhibitors then following it up with a new condition, i hope you get my point.

 

[illixir]

are you guys remembering the drugs that are actually metabolized by cyp450, you always have to connect that in the question, sometimes its easy like warfarin sometimes not, i feel like there's not a good place that gives a list of drugs that give problems from decreased liver metabolism versus renal excretion.

 

[NRAI2001]

A lot of drugs are metabolized by the liver P450 system eg warfarin, but only the inducers and inhibitors can speed up or slow down the system itself.

Basically if the stem describes a situation where the effects of a drug is greater than expected suspect an inhibitor, if less than expected suspect inducers, it will be impossible to learn every drug that is metabolized by the p450

Another way is describing a condition in which the drug of choice is one of the inducers or inhibitors then following it up with a new condition, i hope you get my point.

Thats a really good point about less than or greater than expected effects... I guess most questions probably boil down to that.

Some of the drugs often mentioned when it comes to inducers/inhibitors that are NOT inducers/inhibitiors themselves but ARE effected by inducers/inhibitiors that I ve seen come up a lot are: digoxin, warfarin, OCPs, theophylline...... maybe would could start a list??

 

[kryptik]

I believe kaplan pharm has a list bigger than whats in FA so check it out

 

[Mah]

are you guys remembering the drugs that are actually metabolized by cyp450, you always have to connect that in the question, sometimes its easy like warfarin sometimes not, i feel like there's not a good place that gives a list of drugs that give problems from decreased liver metabolism versus renal excretion.

I don't think its possible to memorize ALL the drugs metabolized by CYP450, I always do what kryptik said, see if the drug is producing more effect than its supposed to- which will link it to an inhibitor, or less effect than it's supposed to and link it to an inducer. I remember the inducers and some common inhibitors, and these are usually easy questions on UW for me.