CYP Inhibition

[neuroiscool42]

Mr. Jones has been taking cimetidine for one year to prevent recurrence of his ulcer. Hisphysician is planning on starting him on ketoconazole to treat a life threatening fungal infection.What would be your recommendation to his physician? Choose the best answer. It is given that both drugs are CYP3A4 inhibitors.
A.Mr. Jones should not be started on ketoconazole since he may experience more ketoconazole induced toxicities. He should be started on another anti-fungal medication.
B.Mr. Jones should stop taking cimetidine.
C.Mr. Jones should be started on ketoconazole
D. Mr. Jones should not be started on any anti-fungal medications

I would definitely rule out D. I wouldn't stop cimetidine either since that would allow recurrence of the ulcer. I am thinking of ruling out C as well because I think having CYP3A4 be inhibited by both drugs would not be good for metabolisms of toxins. Anybody else have any ideas?

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[KVBane]

Cimetidine is a antihistamine that is already no longer widely used due to the side effect profile, and newer ones are already on the market.

I would think B would be the answer, and thus started on a different anti-histamine.
I dont know much about ketoconazole, so I dont know if it has also been replaced, or if its the only treatment. But more importantly, its life threatening, so the ketoconazole is the only thing that must stay.

 

[neuroiscool42]

Cimetidine is a antihistamine that is already no longer widely used due to the side effect profile, and newer ones are already on the market.

I would think B would be the answer, and thus started on a different anti-histamine.
I dont know much about ketoconazole, so I dont know if it has also been replaced, or if its the only treatment. But more importantly, its life threatening, so the ketoconazole is the only thing that must stay.

I think for the purposes of my undergrad pharmacology class, all the medication is still okay to use. The main concept my professor is testing here is inducer/inhibitors of cyp and whether we should use ketoconazole, a drug that inhibits the same CYP enzyme as cimetidine.

 

[Amygdarya]

I think for the purposes of my undergrad pharmacology class, all the medication is still okay to use. The main concept my professor is testing here is inducer/inhibitors of cyp and whether we should use ketoconazole, a drug that inhibits the same CYP enzyme as cimetidine.

Ahem, no, it's the other way around, as KVBane pointed out. Ketoconazole should be used for the life-threatening infection in question (and there are not that many antifungals to choose from). Cimetidine, on the other hand, should be stopped because it inhibits ketoconazole metabolism, thus effectively increasing it's concentration in the body, which can lead to toxicity (and systemic antigungals are not benign to patients by any means). Cimetidine, on the other hand, is used for prophylaxis of stomach ulcers/bleeding - which by itself has been questioned in the past few years - and can be stopped.

Also, SDN is not the place to do your homework.

 

[neuroiscool42]

Thanks for the clarification. And no, this wasn't homework. I was trying to figure out a question from an old exam.