Question About Quinidine

[MediCane2006]

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Okay, so 1 week before D-day and I'm so thrilled to be almost done!! I was leafing through FA today and chatting with my friend who is in Pharm school at Nova....and she was quizzing me on some drugs. When we came to the drugs that interact with hepatic P450, she asked me which were the inhibitors. So I rattled off the list and she said, "You forgot QUINIDINE, that's an inhibitor also.

I told her that no, it's listed as an inducer in the 2004 FA. She got all mad and started quoting intimidating Pharmacology texts at me. So I decided to do some research on my own. As far as I could tell Lippincott Pharm doesn't discuss whether Quinidine induces or inhibits CytP450. But with some online research I came across a couple of articles that indicated that it INHIBITS P450, including this quote from RxMD:

"Drugs known to be inhibitors of the cytochrome P450 system include: azole antifungals, cimetidine, cyclosporine, erythromycin, quinidine, terfenadine and warfarin."

I'm certainly not going to take either source as gospel until I do some confirmatory research, but I'd just like to know whether anyone has a source they could consult to check this out. It may just be a typo in FA (goodness knows there's enough of those) or my pharm friend may just not know what she's talking about. But now I want to know for sure....

 

[Idiopathic]

I thought you were right, and then I researched it. quinidine inhibits cyp2D6 and cyp3A4. I dont really know how to resolve this with everything else I have been taught, so I will probably just remember it as an isolated incident. NO sources on quinidine as inducer, by the way, but about 100 on quinidine as inhibitor.

 

[MediCane2006]

Let's give FA the benefit of the doubt and call it a typo as opposed to a real error 😀 and you're right, in the grand scheme of things it's probably fairly unimportant.

 

[Idiopathic]

My Pharm professor gave us a mnemonic in class the other day that had quinidine listed as an inducer...i dont think he got that from FA. But I cant find anything to back it up.

 

[Stinger86]

File this one under "probably won't see on step 1"

Sometimes I think little things like this exist merely to provide material for pharm students to argue with us.

 

[MediCane2006]

If I see this on Step I, I swear I'm going to start laughing my &ss off and will probably get cited for IRREGULAR BEHAVIOR. I'll let you guys know....

 

[mjl1717]

I would not say its unimportant or would not be seen on step1 when one drug decreases metabolism of a second drug by inhibiting CYT.P450,thus increasing the half life!!

 

[annushka]

In my Kaplan Pharm book, it says,
"CYP2D6 is inhibited by haloperidol and QUINIDINE; not inducible"

I trust them...I heard they usually check their books for correctness.

It's on top of p.10 in the COMLEX Pharm book, if anyone wishes to double-check.

 

[MediCane2006]

It just goes to show you can't trust everything you read in First Aid (or many other board review books for that matter). The good thing is that it seems to be pretty strong on the major concepts. The bad thing is that I'm going to have to revise the clever mnemonic I invented for the drugs that induce p450.... 🙄

 

[Idiopathic]

The bad thing is that I'm going to have to revise the clever mnemonic I invented for the drugs that induce p450.... 🙄

You and the rest of the world, apparently. Honestly, I wouldnt change the mnemonic, because you are more likely to remember it as is and not very likely to get a Q about quinidine, as opposed to pneytoin or erythromycin.