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Pet Rats/Bad breath?


My rat has what appears to be really bad breath and I am wondering if there is a way to take care of it or if it means something bad. She is about 2.5 years old and in great health. She did have surgery a few weeks ago to have a benign mammary tumour removed, but her surgical scars have nearly completely healed and she is back to her normal active self. I only noticed the bad breath yesterday. Her appetite and water consumption are normal, and as I mentioned before she is not acting strangely or different. Her diet has not changed, and is the same diet I also feed to my other rat, who does not have bad breath. The only medicines she had after her surgery were painkillers that she only took for a few days.

Hi Aya,
A bad smell is usually caused by a bacterial infection. This could be in her mouth or in her nasal cavity. I recommend getting her on amoxicillin. See the info below. I recommend keeping her on it probably for the rest of her life as these type of infections tend to be hard to clear up completely, and most rats tolerate being on antibiotics long-term very well.

Based on my 30 years of experience, for a rat who is sick, no matter the symptoms, amoxicillin is the first treatment I recommend. This is because amoxicillin is best for secondary infections, which can get very severe very quickly, killing a rat in a matter of hours or days, and require immediate treatment. Baytril is not always effective for secondary infections, so if you try it first, the could die. Therefore, I recommend all rat owners have amoxicillin on hand. If the amoxicillin doesn’t work within 2-3 days, then you can try doxycycline or Baytril for mycoplasma, which is a slow chronic disease, so you usually have more time for treatment. Secondary infections can cause respiratory symptoms (but not always), lethargy, poor appetite, and other symptoms, and are common in rats, especially young rats and those from pet shops. Older rats can also get secondary infections on top of mycoplasma. Amoxicillin is also best for abscesses.

All vets will have amoxicillin, and in the U.S. you can also get amoxicillin over the counter as aquarium fish capsules from some feed stores and specialty aquarium stores, and online. Call the stores in your area and ask before driving there.  Do NOT tell them you are buying it for your rats!  It is legal for them sell it over the counter only for fish.  You will not find it at Petco, PetSmart, etc.  If you can’t find amoxicillin, you can use ampicillin which is basically the same thing, it just isn’t absorbed as well, so just double the dose to 20 mg/lb twice a day. Be sure to get CAPSULES.

Some vets won’t prescribe amoxicillin for rats because they learn in vet school that you can't give amoxicillin to hamsters or guinea pigs (it will kill them) so they sometimes generalize this to all rodents.  But amoxicillin is fine for rats and mice, whose digestive systems are very different from quinea pigs and hamsters.  I use it all the time.  (For more about getting your vet to prescribe amoxicillin, see the info at the bottom.)

Rarely you will have an individual who will be allergic or sensitive to amoxicillin, and the most common side effect is diarrhea.  In most cases, this diarrhea is mild enough to be controlled with probiotics (good bacteria for the intestines) but if the diarrhea is severe it will stop when you discontinue the treatment with amoxicillin.

You can order amoxicillin capsules from If your rat is already sick, be sure to ask for overnight delivery! They will even ship OVERSEAS!

You can also get amoxicillin mail order from Jedd’s Pigeon Supplies at 800-659-5928.

You want to mix the amoxicillin in a yummy liquid such as Ensure or slightly diluted Hershey’s strawberry syrup. You can buy a 1 ml syringe for measuring at most pharmacies. A 3 ml or 12 ml syringe is also helpful for measuring out the flavoring. Amoxicillin does not dissolve but forms a suspension. The powder will sink to the bottom, so before taking out a dose, you need to stir the mixture with the syringe extremely well, being sure to scrape up all the powder off the bottom so it is in suspension.

Mix one capsule of 250 mg amoxicillin in 7.5 ml of flavoring (If you have 500 mg capsules, use twice the amount of flavoring: 15 ml.) A small pill bottle is about the right size to mix it in.  Keep in the refrigerator.  Amoxicillin doesn’t taste too bad to most rats and most rats will eagerly lick this right from the tip of the syringe.  The normal dose is 0.3 ml/lb twice a day.  You can go as high as 5 times that normal dose if necessary, and it’s a good idea to give a double dose the first time.

If your rat won’t take the amoxicillin mixture voluntarily, you can try mixing it in yummy soft food. Or, you can make the dose 0.1 ml which is too small for them to spit out when you put it in the back of their mouth.  Mix one capsule with 2.5 ml of flavoring. Then the dose is only 0.1 ml/lb twice a day.

You need to know about how much your rat weighs. The normal dose is 10 mg/lb twice a day but you can safely go as high as 50 mg/lb if needed. A 250 mg amoxicillin capsule contains 25  1-lb doses.  

Give the dose twice a day.  If it's going to work the symptoms should improve within 2-3 days.  If it does work you need to continue the treatment for at least 2-3 weeks.  If it doesn’t work then you need to try a different treatment.  If the symptoms are all gone within 3 days you should continue the treatment for 3 weeks.  If it takes longer for all the symptoms to go away, give it for 4-8 weeks and maybe longer.  The longer it takes for all the symptoms to go away, the longer you should continue the treatment.  If the symptoms stop improving, or if the amoxicillin doesn't help at all, you will need to try doxycycline instead.

You can get doxycycline from Jedd’s Pigeon Supply. Most people will want to order Doxysyrup, which is 10 mg/ml. The normal dose is 0.25 ml/lb twice a day. If necessary you can give twice this.

If you own a lot of rats, the most economical choice is Doxyvet Liquid, which is 50 mg/ml. The normal dose is 0.05 ml/lb twice a day. If necessary you can give twice this. It works best to dilute it with flavoring. If you mix 1 ml of the Doxyvet with 5 ml of flavoring, and then the dose is 0.3 ml/lb twice a day. Depending on the flavoring you use, the mixture should probably be refrigerated.

You can also find 100 mg capsules or packets of doxycycline from some sources. In this case, mix one capsule or packet with 12 ml of flavoring (slightly diluted strawberry syrup works good) and then the dose is 0.3 ml/lb twice a day. Store in the refrigerator and stir before taking out a dose.

You can buy 100 ml of 10% oral generic Baytril (enrofloxacin but they call it Enroxil) from pigeon supply companies for birds. The dose for a 1-lb rat is 0.1 ml, which means that 100 ml is 1000 rat doses!  Very economical.   You need to give it twice a day.  Do not refrigerate the Baytril!

I’ve had the best luck giving Baytril in 4-6 ml of a product such as strawberry Ensure or Boost in a baby food jar lid, or in 1/8 teaspoon of the soy baby formula powder, making a paste.  It helps if you put the baby food jar lid on a small magnet to help keep your rat from tipping it over.  

You can also order it from Jedd’s Pigeon Supplies, or or

Jedd’s Pigeon Supplies is my favorite. I order by phone at 800-659-5928. You can also order it on their website at If ordering online, order item #5002.  It won’t say it’s Baytril, as they keep it quiet.

You will find more info about treating respiratory infections on my website at on the Rat Info page.  I also highly recommend you order my Rat Health Care booklet.  It is only $7 plus $2.25 shipping (CA residents add 58 cents tax.)  The address is Rat Fan Club, 857 Lindo Lane, Chico CA 95973.

Concerning amoxicillin and veterininarians:  Many vets don’t want to use amoxicillin on rats.  This is probably because in vet school they learn that amoxicillin can’t be used in guinea pigs, rabbits or hamsters (because it kills the good bacteria in their intestines), and they probably generalize this to rats and mice.  However, rats and mice usually tolerate amoxicillin quite well.  In my experience only a very small percentage of them will get diarrhea from it, and this is not life-threatening; it will usually clear up with a probiotic, or the amoxicillin can be stopped.

Here are some references for using amoxicillin in rats for your vet to check if they are reluctant to prescribe amoxicillin:

Exotic Animal Formulary, Third Edition, James W. Carpenter, MS, DVM editor, Elsevier Saunders Publishing
Page 377, Antimicrobial and antifungal agents used in rodents.
Ampicillin for mice and rats: dosage 20-50 mg/kg PO, SC, IM q12h
(Note: ampicillin and amoxicillin have essentially the same adverse reactions and effectiveness, so they can be used interchangeably)

Blackwell’s Five-Minute Veterinary Consult: Small Mammal, Second Edition, Barbara L. Oglesbee. 2011 John Wiley & Sons, Inc.
Page 588, For Bacterial Infection
For rats (do not use in hamsters), amoxicillin/clavulanic acid (12.5–15 mg/kg PO q12h) may also be used.

ViN (Veterinary Information Network, Inc.) Website

Thomas Donnelly, BVSc on 02/05/2006  “Amoxicillin is safe to give rats.”

Johanna Briscoe, VMD, on 07/08/2004  “I have used Clavamox liquid in a rat and it worked beautifully on an abscess that I thought may have been from a bite….  Clavamox dose same as in other mammals—13.75 mg/kg PO BID.”
(Note: Clavamox is the brand name for a mixture of amoxicillin and clavulanic acid.)

Elizabeth Mitchell on 06/01/2007  “I have used Clavamox a few times in rats without problems, although I am always very careful to warn owners to watch for diarrhea.  I  generally have gone with a dose more similar to dogs and cats (20-30 mg/kg BID) but if you search on PubMed you will find all sorts of much higher doses.”

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Debbie Ducommun


I can answer any questions about pet rats, but you will probably be able find answers to simple questions more quickly on my website at If you have a life-threatening emergency you can try calling me at 530-899-0605. I am not usually on the computer on the weekend.


I have been "The Rat Lady" since 1985 and am recognized as one of the world's experts on pet rats. I have 3 published books and already answer lots of questions about rats daily.

President of Rat Assistance & Teaching Society

I am a monthly columnist for Pet Business magazine, and my writing has appeared in other magazines. I have 3 published books.

BA in Animal Behavior

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