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Please ASAP re: dangers of fenbendazole (Panacur)

22 10:03:53

Question
QUESTION: Hi Dana and thank you for past help.  This is about Frederick again, he had hind leg lameness for a couple of weeks, was put on a high dose of Metacam 1cc twice/day then lowered as I saw fit.
He began doing very well and was using his legs again.  The vet figured it was a pinched nerve.  She had taken x-rays to rule out other scenarios.

A few days ago, he began dragging his back legs again much to my dismay.  I took him to the vet today (same one) and asked her if she would please let me try the Panacur on him.  She reluctantly let me get it.  I've had bunnies on Panacur before without blood tests, etc. even from our vet who deals more with 'exotics' than this one.

She looked at me very seriously and claimed that Panacur is a powerful drug and that I could kill him.  I felt angry inside but asked her why.  She said it could attack the liver or something like that.  I've read about liver enzymes going up but will come down again once the drug is stopped.  She said 'No, there's a chance he could die'.

Now, even tho' I've given him 1 dose already today, I'm worried.  I only wanted to try another remedy as others from Etherbun or my forum www.ontariorabbits.org keep saying 'try Panacur because E.Cuniculi can cause hind leg lameness'.  I don't know whether to give him another dose tomorrow or not.  This vet is completely against hearing about outside information so I will not see her again for certain conditions.

Please let me know if I'm going to endanger Frederick continuing Panacur.

Thank you,
Paula

ANSWER: Dear Paula,

Panacur (fenbendazole) belongs to a class of drugs, the benzamidazoles, that can--in some species--act as a radiomimetic agent.  That is, its toxicity mimics the effects of radiation.  The biggest concern with the benzamidazoles is irreversible damage to the bone marrow, causing fatal anemia.

Of the three benzamidazoles commonly used for rabbits (albendazole, fenbendazole, and oxibendazole), albendazole is by far the most toxic, and it has been linked to sudden rabbit deaths.  The other two are apparently less toxic, though their use is strongly cautioned for birds, which appear to be particularly sensitive to this class of drugs.  Data for mammals is a lot less worrisome, though a few sensitive individuals may have some reactions.

If your vet told you that Panacur is dangerous to the liver, you might want to direct her to this study:

http://www.springerlink.com/content/h031wh144476p43j/

At least in the species used here, there is no significant effect on the liver from fenbendazole.

If it's any consolation, I know hundreds of people have used Panacur, as directed (our vets prescribe it at 20mg/kg once per day), for their bunnies and I don't know of *any* confirmed cases of radiomimetic side effects.  We have used it on our rabbits with excellent results, and have a "herd" of sanctuary jackrabbits who get it regularly to control strongyle worms (they brought them with them from the airport.  Alas!).

I would not be too worried, but the vet is right to give you the warning.  I'd rather she err on the side of caution than be too cavalier with drugs!  If you are very concerned, then you could ask her about trying ponazuril.  Although this drug is a lot newer than Panacur, and we don't really know all the possible side effects, it appears to be very benign (according to all the literature published on it so far), and we have had good results with it against both E. cuniculi and coccidia.

Hard to know just *how* good with such a small, uncontrolled sample.  But it might be worth a try.

For now, though, I would not be too concerned about the Panacur, given the many, many rabbits who have taken it without any apparent harm.

Hope this helps.

Dana

---------- FOLLOW-UP ----------

QUESTION: Hello Dana and thank you.  

Is it safe using Panacur for 28 days as well as Metacam?  I read that there's a chance of renal failure using these 2 drugs together?  Is that true?

Also, Frederick is 6.1 lbs and the vet is suggesting Metacam twice/day again like before at a high dose both times.  He had been on 1 cc twice/day, and I eventually brought it down in dosage over a couple of weeks as he was doing well.  Now that he's had this 'relapse', she's thinking he should be back on the higher dosage of Metacam to start at least.

I've been told by 2 vets at 2 diff. clinics that rabbits don't keep Metacam in their systems as long as dogs/cats, therefore the reason for 2 doses per day.  

Is a high dose of it that often going to hurt him?  When I suggested that, she claimed "no, and he's not using his legs, is he?"  

I can forget about sending her any outside info but thanks anyway, she told me to be careful about internet advice when she's the one physically looking after the animal, in fact got quite perturbed by it.  Unfortunately I need this clinic for times I can't make it to the city to our 'exotic' vet.

Thank you if you could please answer my above questions!

Paula

ANSWER: Dear Paula,

"Is it safe using Panacur for 28 days as well as Metacam?  I read that there's a chance of renal failure using these 2 drugs together?  Is that true?"

Metacam has some chance of causing renal problems, but this is usually over very long term use.  Some renal damage has been demonstrated with fenbendazole in rats, but this was at quite high dosages (500mg/kg/day and 3000mg/kg/day).  The typical dose given to rabbits for E. cuniculi (which also can cause renal damage, by the way) is 20mg/kg.  Many medications have risks, but you have to weigh those against the benefits and make an informed decision.

Has the vet considered Banamine instead of metacam?  

It's understandable that a vet would caution you about accepting advice from a stranger on the internet.  She doesn't know my credentials or experience, and for all she knows I could be clueless.  I'm not, but she doesn't know that.  But for her to become *perturbed* by it is a little over-the-top.  (I always get nervous when a vets expects a client to give them confidence that one usually reserves for a minor minor god.)  But it's very true that she can see the rabbit and I can't.  I always do caution people that the vet is the one who's treating the rabbit, and I'm only here to give information, ideas and suggestions.

Is your bunny better on the high dose of metacam twice a day?  You could ask her what her source for that dose is, because I know of no experienced rabbit vets who prescribe metacam for use BID.  But we're always willing to learn otherwise, if something works.

Hope this helps.

Dana



---------- FOLLOW-UP ----------

QUESTION: Hello Dana and thank you.  I will only use this vet for certain reasons from now on.  We took Frederick to our rabbit vet yesterday and he found problems with an enlarged bladder and nerve damage causing his bladder to become larger than normal and said it would keep getting larger.  There were other problems too so we unfortunately had Frederick euthanized.

His partner so far is ok, maybe a little quieter.  We put Frederick in their pen when we got home and she spent some time with him.  She seemed to just groom a lot (herself).

When could I re-bond her?  I know rabbits aren't here forever but I don't want to push her either.

Thanks,
Paula

Answer
Dear Paula,

I'm so sorry about the loss of your boy.  How sad.  But I'm glad his mate had a chance to say goodbye.

How soon to wait before introducing her to other rabbits will depend on her personality and how much she's grieving.  I would think that she certainly needs a few days to collect herself, but give her lots of extra love for now.

If she's grieving badly and not wanting to eat, then sometimes a "date" with an eligible, neutered bachelor can snap a grieving bunny out of the funk.  But you also don't want to stress them too soon, so it's a delicate balancing act.

You can contact your local rabbit rescuer for help with the timing and the eligible bachelors here:

www.rabbit.org/chapters

I'm sorry for your loss.

Take care,

Dana