# Can Antihistamine Cause Softer Stool?



## Dallas Gold (Dec 22, 2007)

I'm perplexed. Toby has always had issues digestively and currently he is receiving cobalamin injections twice a month and a daily folic acid tablet after digestive enzyme testing. His stool firmed up once we got him on a good dosage. He was just retested a few weeks ago--all in normal ranges. He is also on a daily half dose of Rimadyl, with Pepcid and Denamarin for his eye inflammation (post cataract surgery). 

Pollen season is hitting us hard here, with counts up to 12,000. After consulting with his veterinarian we added in chlorpheniramine tablets twice a day to help Toby with sneezing and eye rubbing due to the pollens. 

About 3 weeks ago his stools suddenly took a turn for mushy. He's happy, otherwise healthy, but consistently mushy stools. Hubby thought it was the Rimadyl, but I wasn't so sure since he's been on it for a while now. However, it is listed as a side effect:



> Decrease or increase in appetite
> Vomiting
> *Change in bowel movements (such as diarrhea, or black, tarry or
> bloody stools)*
> ...


https://animalhealth.pfizer.com/sites/pahweb/US/EN/Products/Documents/RIM1204126R.pdf

Denamarin's side effects are described as follows:


> There are no known drug interactions or contraindications to the use of silybin/silymarin in animals.25,26 While mild side effects, *such as gastrointestinal upset, itching* and headache, have been rarely reported in primates,25,27,28 no side effects have been noted in dogs or cats.11,14,25,26,29,30 The specific silybin-phosphatidylcholine complex in Denamarin has been evaluated in both acute and chronic use safety studies: an acute toxicity study in dogs using levels greater than 80x the amount in Denamarin revealed no adverse physiologic effects,30 and a chronic toxicity study in monkeys who received greater than 80x the amount in Denamarin for 26 weeks showed no compound-related adverse effects.27


Denamarin Veterinary Information from Drugs.com


It dawned on me this morning, after scooping another pile, that we introduced the antihistamine about the same time the stool changes started. 

I went onto the National Institute of Health website and these are the side effects of his medication:



> Return to top
> Chlorpheniramine may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:
> drowsiness
> 
> ...


Chlorpheniramine: MedlinePlus Drug Information

hmmm...it lists constipation, not softer stool. 

His food is not on any recall list, and he's eaten from two different bags since this started. I'm not suspicious of his kibble....yet.

I'm willing to stop the rimdayl, denamarin and/or antihistamine to see if it improves, but I'm wondering which one I should drop first. The Rimadyl is prescribed by his ophthalmologist and we won't give it without the denamarin to protect his liver, so my first choice to eliminate is antihistamine. Has anyone else experienced softer stools with a dog after starting an antihistamine?


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## CAROLINA MOM (May 12, 2009)

Yes, one of the side effects of an antihistamine can be loose stools-see below:

Look to see if diphenhydramine is a key ingredient in the drug prescribed for Toby as it is in Benadryl.



*Diphenhydramine*​ 
This [COLOR=blue !important][COLOR=blue !important]antihistamine[/COLOR] is generally prescribed to treat and prevent allergy symptoms. It also has sedative properties and can prevent or minimize itching caused by allergies. The drug is a proven treatment against many airborne allergens and its side effects are minimal. 
Diphenhydramine, the chief ingredient of Benadryl, typically causes marked drowsiness, although as more doses are administered, that effect might lessen. Other side effects are dry mouth and loose stool. Your dog might also experience appetite loss, diarrhea and vomiting, but these side effects are less common. 
Many veterinary drugs benefit your dog's health but can cause unpleasant side effects. The most common include diarrhea, vomiting and appetite loss. Contact your vet if your dog develops more serious or prolonged side effects.​ 

Read more: Side Effects of the 4 Most Common Prescription Drugs for Dogs - VetInfo [/COLOR]​


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## Penny & Maggie's Mom (Oct 4, 2007)

I don't have any knowledge to share, but sending good thoughts that you can get this figured out soon.


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## 3 goldens (Sep 30, 2005)

Honey has been on daily Benadryl for 3 years now and never had problems with mush poop. Nor did it ever seem to make her drowsey--but it sends me into a "nap time state" every time I take it.


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## Cathy's Gunner (Dec 4, 2008)

I'm not sure about the side effects, Anne. I'm sure each dog is different and maybe the mixture of drugs could cause it as well. I hope that his stool will firm up soon to put your mind at ease. I'm glad he doesn't seem to be effected by it in his moods. Hugs.....


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## cgriffin (Nov 30, 2011)

My dogs never had lose stools with Benadryl but I also think maybe the combination of all the drugs together could cause Toby's tummy trouble. 
I suppose process of elimination starting with the anti-histamine would be a good idea. I would think the anti-histamine is the one Toby needs least, correct? 
Good luck and I hope the tummy trouble will be resolved fast!


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## Dallas Gold (Dec 22, 2007)

Thanks everyone. He's not on Benadryl, but another antihistamine his vet prefers to use for pollen related allergies (she saves Benadryl for insect stings, etc because she doesn't think it works as well for these pollen issues). It's chlorpheniramine (yellow tablets, generic version of chloratrimatron/ chlortabs I believe). The active ingredient is chlorpheniramine. I am also beginning to think it is the combination of the drugs. He's taken the antihistamine in the past with no issues, so that lends credence to the combination theory of causation. Hubby really wants me to stop the Rimadyl so we struck a compromise--stop all of them to see if it clears up and then consider adding things back in. Until then, I'm keeping him indoors during the day and wiping his fur down to reduce the pollen load! I'm feeling slightly anxious about this because next week we are getting a new fence, reducing his ability to eliminate on our property because we will need to take leashed potty breaks during the day in the neighborhood. It's one thing to scoop sloppy poop from your back yard, but downright embarrassing to take him for a walk in your neighborhood and not be able to clean the grass completely up for them--I'll be bringing a water bottle with a squirt top and plenty of paper towels I guess!


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## CAROLINA MOM (May 12, 2009)

Poor Toby and poor you, so sorry you're both going through this. Hope Toby will be doing better very soon.


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## CAROLINA MOM (May 12, 2009)

DG-I found this chart that was posted on Dr. Matt Allworth's website the Community Vet.

I don't know how accurate this info might be ( my disclaimer so to speak)

It does show Gastro problems with the chlorpheniramine you are using for Toby. I didn't know if the Diphenhydramine was an acitve ingredient in the chlorpheniramine as it is in Benadryl.


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## Dallas Gold (Dec 22, 2007)

Thanks Sandy! That is helpful and worthy of keeping somewhere on the computer.

It's been 24 hours since giving him an antihistamine and Rimadyl and well, I'm slowly seeing it take a better shape. He definitely has a long way to go to total improvement but there is some form now at least and the color is getting back to his normal color. I know TMI, but the stool got lighter on the antihistamines. I hope and pray we see major improvement today and tomorrow because Tuesday is when his back yard is taken over by fence work and we will be doing walks out front. He is feeling great by the way--he did some zoomies for me this morning before leaving for his walk. I always enjoy seeing zoomies, especially for an 8 year old dog!


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## Dallas Gold (Dec 22, 2007)

I made a PDF of that handy chart for anyone wanting to keep a copy on their computers:

View attachment possible side effects of antihistamines.pdf


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## CAROLINA MOM (May 12, 2009)

Zoomies in an 8 year old boy is Fantatsic in my book, awesome to watch.

Glad to hear Toby is doing better today, hope each day shows improvement. 

Thanks for converting the chart to PDF.


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## Cathy's Gunner (Dec 4, 2008)

Great news, Anne! I'm so glad to hear Toby is feeling better. Hopefully the stools will be back to normal soon. Gunner is on Benadryl off and on right now because he has been sneezing and having the reverse sneezes. Doesn't seem to affect him in any way as far as stool or sleepiness. It does seem to help his sneezing. Have a wonderful day with your boy.


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## Penny & Maggie's Mom (Oct 4, 2007)

That's a great chart to have. Thanks ladies. Anne, if it turns out he does need an antihistamine, you may want to ask your doc about zyrtec. Maggie has done really well on it.


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## Dallas Gold (Dec 22, 2007)

Penny & Maggie's Mom said:


> That's a great chart to have. Thanks ladies. Anne, if it turns out he does need an antihistamine, you may want to ask your doc about zyrtec. Maggie has done really well on it.


That's funny--look at the chart- side effects of Zyrtec: Expensive! I'm laughing! Instead of affecting the dog, it affects the owner's wallet!


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## Dallas Gold (Dec 22, 2007)

oh, and I forgot to add, his ophthalmologist was mostly anti antihistamines for dogs for some reason, saying they really didn't help them too much. Obviously he's never owned an allergic golden retriever. I did see a side effect of the chlorpheniramine is vision changes, so, another reason to stop and then switch.


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## Penny & Maggie's Mom (Oct 4, 2007)

Dallas Gold said:


> That's funny--look at the chart- side effects of Zyrtec: Expensive! I'm laughing! Instead of affecting the dog, it affects the owner's wallet!


 
I did see that, but the generic from Sam's isn't too bad.


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