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Benedryl and Revolution Dosage

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Lindsay Gunn

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Hi everyone, I’m hoping you can help. A bit of background my bunny is a 3 pound holland lop and he has had mites that won’t seem to go away since September. We were doing monthly treatments of revolution kitten dose (Mauve) which contained .25ml (15mg) and a concentration of 60mg/ml. Around thanksgiving we switched the dosage to every two weeks.

I went back to my rabbit savvy vet yesterday and after reviewing skin scrapingings and checking for bacterial or yeast, she thinks it could be an allergy or were not breaking the mites life cycle. We decided to put him on an antihistamine for a few days to see if this was the issue. She prescribed 1.5ml of children’s Benedryl (diphenhydramine oral liquid 12.5mg/5ml). Is this the correct dosage? I’ve never given any medication over .9ml before.

If it is not an allergy and the skin flaking doesn’t subside by Friday, we were going to do another dose of revolution using a higher dose.

I was given the Revolution for Dogs 10.1-20lbs with tubes containing .50ml (60mg) of selemectin which has a concentration of 120 mg/ml.

This seems like it would be too high and I’ve read that bunnies should only be given the cat version which was a concentration of 60mg/ml.
Is the dosage correct or should I go back and ask for the cat dosage?
 

JBun

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Because of a rabbits faster metabolism, medication dosages are usually much higher. Revolution(selamectin) dosage for rabbits is usually recommended to be around 18mg/kg, I've seen it recommended even as high as 25mg/kg. Though usually one dose seems to be enough in most cases, I've seen recommendations for giving every 2 weeks. So your rabbit should have been getting around 21mg, though if this was just a basic case of fur mites, the 15mg dose should have been sufficient to eliminate them, as a lower dose is usually enough for those type of mites.



But because your rabbit has been getting it for several months and it hasn't controlled the problem, if your rabbit actually does have mites, they could now be resistant to selamectin. So you may need to switch to something else at this point. And really the only other options are ivermectin and moxidectin. Moxidectin can be a little risky as OD seems to be more of a risk with it's use. Has your vet tried ivermectin injectable or oral yet? It's possible though that this isn't mites but something else, so no antiparasitic would be helpful if this is the case. At any point did your vet ever find any evidence of mites on skin scrapings even at the start, and was a fungal infection checked for? Fungal would be the next most common thing to cause skin problems in rabbits.

MediRabbit (fur mite)
MediRabbit (burrowing mite)
Medirabbit (fungal dermatitis in rabbits)

An allergy could be a possibility, though it would be rare. But if this is the case, often this type of allergy is linked to a food allergy. In which case you may need to experiment with changing pellets, hay, etc to different types. Pellets I think would be the most likely culprit. For the benedryl dosage, your rabbit is getting 3.75mg for 3 lbs of body weight(1.3kg). Listed dosage for rabbits is 2mg/kg every 8-12 hours. 1.1ml would be closer to the listed dose for a 1.3kg rabbit, but 1.5 doesn't seem unreasonable as a dose.

(drug dosages in rabbits: diphenhydramine, selamectin, ivermectin, moxidectin)

There is also the slight possibility of it being something called sebaceous adenitis. Though if this is a possibility, your vet should probably take chest xrays, as a thymoma can sometimes be linked to this occurring. Usually this will rarely happen in older rabbits, but thymomas can cause this type of similar skin condition that can appear to look like a mite skin issue. I had an older rabbit that I thought had mites, primarily presenting with dandruff, scaly skin, and crusting around his hindquarters. He was treated and it seemed to go away initially, but then came back. That's when I noticed he also seemed to have faster and more labored breathing. He had also started to lose weight. The vet took xrays and it showed a shadow in his chest. So he ended up having a thymoma and the skin condition wasn't mites but sebaceous adenitis due to having a thymoma.

Adenitis (sebaceous adenitis in rabbits)



(sebaceous adenitis due to a thymoma in rabbits)
 
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JBun

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The tubes for dogs are fine, just less has to be given because of the higher concentration. The tube you were given of 60mg would be excessive(in my opinion), even if dosing at the highest dosage of 25mg/kg. If you use the dog tube, I would draw the contents into a syringe and give only half that, so only 30mg/0.25ml. But if in doubt, always check with your vet.

If you continue to not find an answer to this skin condition, a skin biopsy might be next in order.
 

Lindsay Gunn

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Thank you for getting back to me! That is very interesting regarding sebaceous adenitis and thymomas... he is a lop and has breathed loudly for quite some time (another issue I can’t get to the bottom of). I eventually started to assume it was due to his facial structure.
The vet didn’t want to do injections of ivermectin because she said some rabbits react poorly to it. She suggested increasing the Revolution amount. I was just really concerned when I saw the 120mg/ml concentration and a dose of .50ml (60mg). He initially was on one that’s dose was 15mg, increasing this by four times the amount seems scary to me.
They did do skin scrapings and tape presses and have never found mites. They sent out a fungal culture for ring worm and it was negative, they also tested for bacteria and yeast and got nothing as well.
I should also add that I bought a students microscope so I could check flakes myself and none of them look like bugs, just scaly skin.
For the Benedryl, I saw this on Medicean it as well but the didn’t mention the concentration. I saw somewhere else someone was only giving their rabbit between .1-.2ml. I just wanted to be sure before I gave him a full ml, not a tenth or 20th of one.
 

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Lindsay Gunn

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Sorry last post:) I just re read the Benedryl bottle and I wrote the description wrong, it is “diphenhydramine oral liquid 12.5mg/5ml”.
Does that mean there is 12.5mg per 5ml? I don’t really understand how to calculate the doses
 

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12.5mg per 5ml means there is 2.5mg per 1ml. I've given my 1.7kg rabbit 1ml(2.5mg) of the childrens benedryl before. Just know it can make them a bit drowsy(like us).

Yes, some rabbits can have a negative reaction to ivermectin. Usually though, it's the ones with dutch or vienna carrier genes, or blue eyed whites, similar to what happens with collie dogs with the MDR1 gene. If your rabbit doesn't have this gene, it's unlikely that ivermectin would cause a negative reaction when dosed correctly. Not impossible, just not likely. Revolution is the safer to use of the two, but if this actually is mites and they are resistant to the revolution, it may become necessary to try ivermectin. Though with no evidence of mites under any scrapings, it doesn't seem the likely cause of the skin condition.

Loud breathing can be a genetic or age related nasal passage or soft palate issue, when it's not due to a serious respiratory condition(eg. pneumonia, airway obstruction). I have some dwarf rabbits that this genetic issue is very apparent in. Several of them snore and have always done this since babies. They also have louder breathing if they get stressed at all.

Loud breathing could be associated with a thymoma, but more often it will be faster breathing, seemingly taking more effort to breath(labored breathing), or getting tired more easily from the increased respiratory effort. You may also see bulging eyes or third eyelid, especially when the rabbits head is down lower, and you may also see a tendency of your rabbit to rest or sleep with the head in an elevated position to take pressure off the chest cavity.

If you aren't seeing any of these additional signs, it might not be a thymoma but just a simple case of sebaceous adenitis, or a different skin condition yet to be determined. If there isn't any improvement with the benedryl or increased revolution dosage, or you don't feel that allergies or mites is the issue, I would next consider having a skin biopsy and/or chest xrays done like I mentioned above.
 
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Lindsay Gunn

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Thank you so much for your reply and that’s exactly what’s happened. After no response to the Benedryl I did another higher dose of the Revolution. The flakes did go away for about six days and then came back at day nine and are worse now then before. My vet recommended doing a biopsy and chest x day as well.
I did have a chest x ray done on him about a year ago due to the loud breathing and being sure it wasn’t pneumonia etc. would thymoma be slow growing or can it show up quickly?
 

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