Biaxin question....

[kellyt]

Has anyone heard of the antibiotic Biaxin being a no-no for Prograf users???

[Chris]

Yes, sort of on Jan 24 from my doctor at my transplant center. She just said we can't put you on that one, so I figured it was due to my immunos. I was put o a z pack instead as one of the usuals.

[kellyt]

Thanks.  I have never been told this and I was on it in November.  Luckily no problems, but it still pisses me off.  Even more reason I want to educate GP's on "no no" drugs for kidney transplant patients.  grrrr!   
I'm really  mad at myself, because I call my clinic for all medications I'm prescribed by other doctors, but I didn't call on that one.   

[RightSide]

Correct.

Biaxin and Erythromycin are potent inhibitors of the liver enzyme Cytochrome P450 CYP3A4 (google that!), which your liver uses to metabolize Prograf.  (The medical jargon is that Prograf, or tacrolimus, is a substrate for CYP3A4.)

If you take Biaxin, the production of enzyme CYP3A4 is inhibited, and so there isn't enough of it to break down the Prograf.  Prograf can then build up to toxic levels.

An antibiotic in the same class (macrolide) as Biaxin that you can take safely is Zithromax.  Zithromax  is comparable to Biaxin in antibiotic potential, yet it does not inhibit production of the CYP3A4 enzyme.  I've taken Zithromax as an alternative to Biaxin.

[kellyt]

Thank you!  That sounds like information I should have received from my doctor.    grrrrr.

[RightSide]

This problem of cytochrome P450 drug interactions comes up again and again. As I'm sure you were told by your docs, even grapefruit juice can inhibit certain of these enzymes.

Here's a chart you can download that shows which common drugs interact this way.

http://medicine.iupui.edu/clinpharm/ddis/

Remember:  If a given drug is a substrate for a particular enzyme, that means that the liver needs that enzyme to break down and metabolize that drug.  Thus the level of that drug in your blood can be affected by any other drug that either inhibits or induces (potentiates) that enzyme.  Too little of the enzyme and the drug will not be broken down quickly enough, potentially building up to toxic levels as you take more doses.  Too much of that enzyme and the drug will be broken down too fast, so you don't get an adequate dose.

In the case we've been discussing, Prograf is a substrate for enzyme CYP3A4, which is inhibited by Biaxin.

[kellyt]

THANK YOU!!!      Good information.  And, yes, I knew about grapefruit, but I don't eat/like grapefruit so no problem there.

[RightSide]

I always wondered about tangelos.  A tangelo is a hybrid cross of a tangerine with a grapefruit.  So if grapefruit causes drug interactions, would tangelos cause drug interactions too?

So I did a little Internet searching and I found this:

http://cat.inist.fr/?aModele=afficheN&cpsidt=17035999

Evidently while a tangelo may contain the same problematic chemicals as a grapefruit, the amount is too low to trigger a drug interaction.

Limes (or lime juice), on the other hand, contains enough of those chemicals to be cautious about consuming limes while on our anti-rejection meds.

http://www.rxlist.com/lime-page3/supplements.htm

I don't eat limes.  But lime is used as a flavoring in some medications (like Alka-Seltzer Lemon-Lime), and those medications should be avoided by those of us on anti-rejection meds.

So it's not just grapefruit.  Gradually we're learning about one or two other fruits that we should be careful about.

[kellyt]

One year later (ok, 13 months) and here I sit with the same problem....a sinus infection.  I saw my allergiest today and he prescribed Omnicef as the antibiotic.  I'm still waiting on a call back from my nephrologist, but thought I would check here in the mean time.  Anyone know if Omnicef is a safe antibiotic for transplant patients?  I asked the nurse to ask my neph what antibiotic IS okay to take for the future if Omnicef is no good but, again, waiting on that call back.   

[coravh]

I would also check with your pharmacist. I have gotten good drug interaction advice from mine. And the response time is often faster than with my docs.

Cora

[RightSide]

Here's a website that lets you search for drug interactions:

http://www.drugs.com/drug_interactions.html

It shows no interactions between Prograf and Omnicef.

However, Omnicef is another one of those drugs that is filtered out of the body by the kidneys.  Hence you gotta drink plenty of water, watch your kidney function, you know that routine by now.