The Rat Fan Club

Respiratory & Heart Disease in Rats

by Debbie “The Rat Lady” Ducommun


Updated 11/29/17

This information is from my booklet Rat Health Care. I highly recommend you order a copy to have on hand! Check it out at Rat Books

Respiratory disease is the most common health problem and cause of death in pet rats. The most common organism causing this disease in rats is the bacteria Mycoplasma pulmonis, which can enter the body’s cells in order to hide from antibiotics.  While antibiotic treatment can help control the disease, there is no known cure for rats. 

Mycoplasmosis is extremely contagious and baby rats contract the bacteria from their mother during birth.  The disease has become so common that pretty much all pet rats are infected, whether they have symptoms or not.  Laboratory rats are free of the disease because in the past, baby rats were delivered by Caesarian section while the mother was submerged in disinfectant, sacrificing the mother.  All laboratory rats in the world are now descended from these hand-fed babies.

The Mycoplasma bacteria live in the lungs, therefore it is incorrect to refer to “upper respiratory infections (URI)” in rats. Mycoplasma commonly causes pneumonia, lung abscesses, emphysema and lung lesions which on autopsy can appear as a “cobblestone” effect on the surface of the lungs.  It can also cause inflammation and bleeding of the uterus.  To see autopsy pictures of rat lungs click here.

A mycoplasma infection makes a rat more susceptible to secondary respiratory bacterial infections as well. The respiratory symptoms that are common in rats can be caused either by the primary mycoplasma infection, secondary infections, or both as well as heart disease. In young rats, symptoms are more likely to be caused by secondary infection, so they need to be treated accordingly.  To see autopsy pictures of rat hearts, click here.

Different rats also seem to have differing resistance to the disease. The severity of a mycoplasma infection can be increased by cigarette smoke, ammonia from a dirty cage, vitamin A or E deficiency, pine or cedar shavings, and a concurrent respiratory infection of another type, as well as genetic susceptibility.

(None of the organisms causing respiratory infections in rats are infectious to humans.  The only diseases I know of that can be transmitted from domestic rats to humans are salmonella and  “rat-bite fever,” a rare bacterial infection similar to cat-scratch fever.  For more info see my article at

Common Symptoms
The first symptom of a respiratory infection is usually frequent sneezing (healthy rats rarely sneeze) which can progress to wheezing.  To hear examples of rats wheezing, click here.  Often, the first symptoms of respiratory disease seen in a rat, especially in young rats, will be caused by a secondary infection.  Mycoplasmosis tends to be a slowly progressive chronic disease that usually doesn’t cause symptoms until the rat is older than 8 months of age. 

For any symptoms, I recommend first trying amoxicillin, which tends to work well for secondary infections.  Secondary infections can become more serious more quickly than mycoplasma, so treat for them first.  If you treat for mycoplasma first, and it turns out to be a secondary infection, the rat may get so sick he dies before you can try the treatment for secondary infections.  Usually a mycoplasma infection is chronic, that is, it starts out slowly with mild symptoms that gradually get worse over a period of weeks or months, so quick treatment for myco is not as critical as it is for a secondary infection.  I recommend that all rats owners have amoxicillin on hand so sick rats can be treated ASAP.


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)


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.”


When treating respiratory symptoms in rats with amoxicillin, if the symptoms do not improve within 3 days of treatment, then you should switch to doxycycline, which tends to work well for mycoplasma. 

Symptoms of advanced lung or heart disease can include labored breathing, weight loss, blue extremities, and respiratory distress, which can cause a rat to gasp through her mouth or become agitated and dash about in panic.  For the treatment of respiratory distress, see the article on  First Aid.  If treatment cannot prevent such attacks, euthanasia is the kindest action.


Mycoplasma usually causes only respiratory symptoms.  Other symptoms such as loss of appetite, lethargy, rough coat, and hunched posture are usually caused by a secondary infection or other disease, and should be treated immediately with amoxicillin.  A rat who is extremely lethargic and refuses to eat or drink needs amoxicillin force-fed. 


An infection can also damage the nasal cavity resulting in bleeding, which can be fatal. Nasal infections are difficult to cure and should be treated long-term with amoxicillin.

(For how to mix and use amoxicillin see “Giving Medications” and “Mixing Medications in a Liquid” below.)

Rats with mycoplasma (all pet rats) will frequently exhibit a behavior that is often mistaken for hiccups. The rat experiences rhythmic jerks of his body for between several seconds to several minutes, usually about 2 jerks per second. Sometimes a sound can be heard at each jerk, but often there is no audible sound. This is not hiccups. It is a sneezing jag caused by the mycoplasma respiratory infection. In both coughing and hiccups air is expelled from the mouth. When rats exhibit this behavior, you can see that their mouths remain closed and air is only expelled through the nose, therefore it is sneezing, not coughing or hiccups. I know it is caused by mycoplasma because lab rats, who are myco-free, never do it. If your rats only do it occasionally, you don’t have to worry about it. But if they do it a lot, or if they start doing it more often, then you want to treat it with antibiotics that work for myco. I recommend starting with doxycycline.


Secondary Infections

Mycoplasma makes rats more susceptible to secondary bacterial infections from a variety of bacteria.  These infections are usually opportunistic, taking advantage of a break in the immune system, and are not usually contagious, but they can be deadly, and sometimes within just 12-24 hours!  For this reason, I recommend that amoxicillin be the first antibiotic tried in most cases.  If your rat appears at all sick or lethargic, I recommend starting him or her on amoxicillin ASAP!  That is why I recommend all rat owners have amoxicillin on hand at all times.


If a rat appears quite ill, then it is a good idea to give both amoxicillin and enrofloxacin at the same time.  Both are bacteriocidal and work well together.  Amoxicillin can also be used in combination with doxycycline, because they work on different bacteria.  Another good combination for severe symptoms is gentamicin and amoxicillin. (Gentamicin must be given by injection as it is not absorbed by the digestive tract.)  Both of these combinations target secondary infections as well as mycoplasma.  I recommend treating secondary infections for a minimum of 2-3 weeks or until symptoms have been gone at least a week.


There is controversy whether rats can get strep from a human with strep throat.  The organisms are supposed to be different (Streptococcus pyogenes for strep throat, Streptococcus pneumoniae for rats) but there have been some suspicious cases.  It is probably best for someone with strep throat to avoid rats.


Some books say that rats can get “colds,” but they mean respiratory infections.  Rats cannot get the human cold or flu.


Viral Infections                                    

There are two viruses that can cause respiratory symptoms in rats.  Sendai virus causes a true respiratory infection.  Sialodacryoadenitis (SDA) virus is an infection of the salivary glands, but symptoms can include sneezing, wheezing, runny eyes and nose, labored breathing, swelling of the glands under the throat, bulging eyes and sudden death. 


In mycoplasma-free lab rats these viruses are not usually fatal to post-weaning rats and the rats recover in a week or two.  (Sendai can cause a stuffy nose in infants which can prevent nursing and cause death.)  However, for rats infected with mycoplasma, a viral infection can result in fatal secondary infections.  In fact, the first indication that a rat colony has been infected with a virus can be the sudden death of one or two rats.  The disease is usually more severe in older rats. 


You can’t treat the virus, but you can treat the secondary infections that cause the most danger.  Sometimes treatment with amoxicillin or amoxicillin and enrofloxacin (Baytril) is enough, and sometimes gentamicin with either amoxicillin or cefadroxil is necessary.  Aggressive supportive therapy, including an injection of dexamethasone for inflammation, and fluids, might be necessary. Treatment with ophthalmic ointment may be necessary to prevent eye damage.


Both viruses will die out in a population within 60 days if there are no new rats or babies.  Charles Rivers Laboratories says the SDA virus is only shed for 7 days, but an infected rat will usually have antibodies to the virus for the rest of her life.


Disease Transmission & Quarantine          

Most pet rats get mycoplasma directly from their mother during birth and so have it all their lives.  Infected rats can transmit the disease to mycoplasma-free rats (lab rats) through direct contact or repeated exposure through the air.  Because lab rats don’t get mycoplasma at birth, if they are exposed later they seem to be more resistant to it. 


The rat viruses and some secondary bacteria can be spread both through direct contact and through the air.  Apparently, the SDA virus can live for 3 hours on inanimate objects, and longer in the human nasal tract, so after being around strange rats it is best to blow your nose and wait 3 hours before going home or visiting other rats.


When bringing a new rat into your colony, a quarantine is only necessary if the rat has been exposed to new rats in the previous 2 weeks. If the new rat

has been in the same living situation for the last 2 weeks, a quarantine shouldn’t be necessary.  If the new rat has been exposed to other new rats in the

previous 2 weeks, or when bringing rats home from a show, it is best for them to be quarantined for at least 1-2 weeks before exposing them to your other

rats.  Ideally there should be no air-flow between your rats’ room and the quarantine area.  Wash thoroughly and change your clothes after being with the

quarantined rats.


Other Causes of Respiratory Symptoms

Some rats are sensitive to some beddings—most commonly CareFRESH—and can sneeze when exposed to them. Pine and cedar shavings, which are toxic, can cause sneezing.  I recommend using rabbit food as bedding in rat cages. It is cheap in big bags from a feed store and very good at controlling odor. 


Allergies are rare, but can occur.  I know of a rat who wheezed in response to yogurt drops, and 2 brothers who sneezed when exposed to dogs!  The most common foods to cause allergies in rats are peanuts and dairy products, including yogurt drops.


Congestive heart failure, which is also very common in rats, can also cause respiratory symptoms. Lung tumors are very rare.  Since 1985 I have done gross autopsies on more than 250 rats and I have seen only 2 lung tumors, although  I have seen 4 chest lymphomas.

Most respiratory symptoms in rats are caused by respiratory infections or heart disease, but tumors in the chest can also cause labored breathing. It is very rare to find a lung tumor in rats. Since 1985 years I have done gross autopsies on more than 200 rats and I have only seen two lung tumors, but lymphomas of the chest are more common—I have seen 7 of them.

Inner Ear Infections

Inner ear infections are common in rats. They may be caused by mycoplasma or a secondary bacteria such as Streptococcus moniliformis or Pseudomonas. The infection causes inflammation in the inner ear, affecting the rat’s balance. This will cause the rat to hold his head tilted to one side. This is why some books call this disease “wry neck” but it has nothing to do with the neck. Without treatment, the loss of balance can get so bad the rat will roll over and over and is unable to eat, therefore, immediate aggressive treatment is necessary. A rare possible side effect is facial paralysis (see my Rat Health Care booklet.)


 I recommend treating with either enrofloxacin and amoxicillin together, or chloremphenicol. An anti-inflammatory must also be given to reduce the swelling in the ear. Dexamethasone or prednisone is best. If necessary you can also try ibuprofen. If the treatment is going to work, you should see significant improvement within 2-3 days. If not, switch antibiotics. Continue treatment until symptoms are gone for a week or until it has been a week since you have seen any further improvement. At this point it isn't likely to improve any more. An inner ear infection can result in a permanent head tilt, even if treated, but a mild head tilt won’t affect the rat much.


Treating Mycoplasma

The antibiotics that tend to be most effective against mycoplasma are doxycycline and enrofloxacin.  There are different strains of mycoplasma that are more or less resistant to various antibiotics.  In some cases, a strain will respond best to both doxycycline and enrofloxacin together.


Because mycoplasma is a very resistant organism, treatment must be persistent.  Humans can contract a version of mycoplasma which is a different disease than what rats get (humans get Mycoplasma pneumoniae) and when they do the treatment is antibiotics for 1-2 years!


I recommend treating mycoplasma for at least 6-12 weeks at a time or even much longer.  An older rat with chronic symptoms and/or heart disease should be on enrofloxacin and/or doxycycline for the rest of his life.   Both these antibiotics are usually well tolerated by rats for long periods of time.  I have had some of my rats on enrofloxacin or doxycycline for over a year with good results, and one of my vet’s patients lived to be over 4 years old and was on Baytril the last 2 years of her life!


Other Respiratory Medications

If your rat’s nose seems congested, the decongestant pseudephedrine might help (use carefully in rats with congestive heart failure).  Buy the non-drowsy pediatric formula. A product also containing guivesan seems to dry them out less.  The dose is 1.5 mg/lb, 3 times a day. An antihistamine can be helpful in some cases, and especially, of course, if the symptoms are caused by an allergy. For doses, see my Rat Health Care booklet.  Remember that these medications only treat the symptoms, not the cause.


A bronchodialator can be very helpful in rats with labored breathing or respiratory distress.  The one I use the most is aminophylline, but I have also used theophylline for a rat who hated the taste of aminophylline.  Aminophylline can be given either orally for long-term treatment or by injection in an emergency. The dose for aminophylline is 2.5-5 mg/lb 2 to 6 times a day. You can also try Primatene tablets which are available over-the-counter. Try a dose of 1 mg/lb 2 to 6 times a day.


An anti-inflammatory can also be very helpful to reduce inflammation in the lungs.  Ibuprofen has been helpful in several cases, and I use prednisone extensively.  The dose for ibuprofen is 60 mg/lb. For more info on giving it, see the First Aid section on the Rat Info page. The dose for prednisone is 1 mg/lb twice a day. For severe acute infections, an injection of dexaphosphate or dexamethasone, at a dose of 1 mg/lb, are stronger.  You should see improvement within 12 hours. 


If there is excess fluid in the lungs, a diuretic can be helpful.  I’ve had good results with Lasix (furosemide) at a dose of 1-2 mg/lb 1-3 times/day.  You should see improvement with oral dosing within 12 hours, and with an injection in a few hours.  Vitamin B6 can also act as a diuretic.   I suggest trying 5-10 mg per day.  When a rat is on a diuretic, you must frequently check him for dehydration by pinching the skin on his back.  In a rat who is normally hydrated, the skin will snap back immediately.  The longer the skin takes to snap back, the more dehydrated a rat is.  If a rat on a diuretic becomes dehydrated you must stop the diuretic and get the rat rehydrated.


Treating Congestive Heart Failure

I have found that rats with advanced respiratory disease often have congestive heart failure as well. The recommended treatment for heart failure is a low sodium diet, enalapril (1-12 mg/lb twice a day), which lowers the blood pressure and makes it easier for the heart to beat, and atenolol (1-4 mg/lb twice a day), an beta-blocker that slows the heartbeat to make it more effective.  (The American Heart Association recommends the use of beta-blockers for most patients with congestive heart failure.)  Enalapril is so safe it can be used as a diagnostic tool.  If giving enalapril improves your rat’s symptoms, then you know he has congestive heart failure.  If enalapril is going to help you should see improvement in the rat’s symptoms within 1-5 days.  A diuretic can also help in some cases.  For more information about congestive heart failure, see my Rat Health Care booklet.


Other Treatments

Moisturizing the air with a humidifier can help some rats breathe more easily. 


A product called VetRx or FerretRx can help in some cases.  It is aromatherapy that works by stimulating deeper breathing and contains Canada balsam, camphor, oil origanum, and oil Rosemary.  The best results seem to come by putting a few drops in the nest box or on the bedding where it will be inhaled 2-3 times a day.  Do not rub it on your rat’s nose as this seems to cause discomfort for some rats.  When using it, try alternating one week on, one week off.  It seems to cause irritation if used continuously.  Look for these products in pet shops and feed stores. Another essential oil that can help is eucalyptus, or you can use Vicks Vaporub.


If a rat is having gasping attacks, he will swallow large quantities of air which he can’t burp up.  This will cause stomach distension and discomfort.  In severe cases it can press on the chest and make the breathing worse, so the air must be removed from the stomach through needle aspiration.


If the rat is no longer gasping (a rat in respiratory distress will not be able to take oral medications) but still has a distended stomach, you can try using the product Gas-X.  Try giving about ¼ teaspoon.


When a rat is experiencing severe labored breathing or respiratory distress, oxygen therapy can be beneficial.  It can make the rat more comfortable while you wait for medications to work.  Gas oxygen must be prescribed by your vet.  You can rent or buy bottled oxygen, and you can also buy a machine that concentrates oxygen out of the air.  Used oxygen concentrators are sold on eBay without a prescription for around $200-300.  You can use a 10-gallon aquarium as an oxygen chamber, or make a chamber as for nebulizer treatments (see below).  The rat will need to live in the chamber until other treatments insure comfort outside the chamber.  Don’t forget a water bottle.


If respiratory symptoms do not improve in an oxygen chamber, it means the lungs are not capable of oxygen exchange, and the rat should be immediately euthanized.


Aggressive Treatment

You can significantly improve the health and life span of most rats with respiratory disease by treating all symptoms promptly, continuing antibiotics for the treatment periods I’ve recommended, and trying new medications if one is not working. Treatment for heart disease is also important.


Even if your rat becomes very sick, don’t give up. I’ve seen several rats pulled back from the brink of death after receiving the correct medications, recovering their health to live for several more months.  Although respiratory and heart disease are extremely common and can be devastating, prompt and persistent treatment with medications that work for your rat can help keep the diseases in check in most cases, and will usually allow your rat to enjoy a long happy life.


Giving Medications

The easiest way to give medications is to mix them into a yummy liquid. To do this you need syringes for accurate measurement. For capsules, just pull them open and dump out the contents into the flavoring. Most tablets will dissolve in a liquid overnight, but they can also be ground up for immediate mixing. Some ideas for the flavoring are: Ensure, powdered soy infant formula mixed up fairly thin, soy milk or almond milk plain, or flavored with fruit syrup, slightly diluted strawberry sundae syrup or pancake syrup (try blueberry), or molasses diluted 1:1 with water.  Flavored syrups may also be available from your vet or pharmacist.


If you don’t have syringes for measuring, you can grind tablets or the contents of a capsule into a fine powder on a small plate with a spoon and divide the powder into the proper number of doses. You can then mix each dose in food.  Some suggestions for foods to put medications into include baby food, pudding, mashed avocado, yogurt, brown sugar and carob powder, honey, peanut butter mixed with jelly, moistened graham cracker, non-fat cream cheese, margarine, Nutri-Cal, pasta sauce, and as a last resort, ice cream, frosting, cheesecake, or even butterscotch or chocolate syrup!  Use only enough food to mask the taste of the medicine so your rat will eat it all immediately.  Adding a bit of salt will help counter the bitter flavor of medicines.  If your rat refuses to eat the doctored food voluntarily, those in paste form can be smeared on his mouth, or even on the backs of his ears so he will groom the paste off and eat it.


If a rat dislikes the taste—or the aftertaste—of a liquid, it is still possible to administer it if you give only 0.1 ml at a time. You can force this tiny drop into the back of a rat’s mouth and it’s too small to be spit out.


The dose for ibuprofen is 15-60 mg/lb 2 to 4 times a day.  You can use you can either crush up a tablet or use liquid baby medications. Most rats like berry flavored Motrin.  To figure out the dose, look on the bottle to see how many mg/ml.  Figure out how many ml to use to give your rat the proper number of mg.  It’s a good idea to give the rat a treat afterwards to mask the bad aftertaste that may cause your rat to refuse the medication the second time.


Antibiotic Treatment
Antibiotics are different from other drugs in that they don’t work directly on the patient; instead they work on bacteria inside the patient’s body.  In general, it is better to give a higher dose rather than too little as the levels in the blood must be high enough to do their job.  Antibiotics must be selected carefully not only according to what type of bacteria may be causing the infection, but also how the antibiotic works, what tissues of the body it can penetrate, the patient’s state of health, and any possible side-effects.


Antibiotics are divided into two groups according to how they work.  Bactericidal antibiotics actually kill the bacteria but only when they are growing.  Bacteriostatic antibiotics prevent the bacteria from growing, so the immune system can kill them off.  Bacteriocidal types should be used for serious acute infections whenever possible.


Some antibiotics have a synergistic effect, having a greater effect together than when used alone.  This occurs when gentamicin is used with the penicillins, which assist gentamicin in penetrating the bacteria’s cell wall.


Bacterial Resistance

There is some confusion about resistance to antibiotics.  It’s not the patient that develops a resistance to an antibiotic, it is the bacteria.  A particular type of bacteria might develop a way to withstand the action of an antibiotic.  This is more likely to happen when the antibiotic is only given for a short period of time, if it is given off and on, or if it is given at a less than optimum dose.  The bacteria might be able to withstand a short weak attack but not a longer stronger attack.  This is why when treating respiratory infections in rats it’s not a good idea to give an antibiotic for mycoplasma  for less than 6 weeks, or to use antibiotics in a on-off, on-off fashion.  It’s better to use the antibiotic steadily for a long time.  If bacteria become resistant to an antibiotic, then a different antibiotic must be used.  Using two antibiotics together can sometimes also overcome resistance.


Using Antibiotics

If a particular antibiotic is effective against an infectious organism, you should see an improvement in acute symptoms within 2-3 days, or in chronic symptoms in 3-5 days.  Don’t keep using the same treatment if there is no improvement in the symptoms!  With any treatment you should continue to see steady improvement in the symptoms.  If you don’t, try another antibiotic.  (See Flowcharts on page 26-28 of my Rat Health Care booklet.)   If the symptoms come back, restart the treatment and continue it at least twice as long.


When a rat is severely ill, it is a good idea for the first dose given to be extra strong, sometimes twice the normal dose, to get the patient off to a good start. In general, the length of treatment for infections affecting the skin should be at least 10-14 days.  Respiratory and urinary infections generally need to be treated for several weeks. 


I recommend continuing treatment for secondary respiratory infections for at least 2-3 weeks, or until the symptoms have been gone for at least two weeks.  In cases of chronic respiratory infections, treatment can and should be continued for longer than this.  However, some antibiotics, such as gentamicin and chloremphenicol should not be used longer than 14 days.  For mycoplasma the course of treatment should be at least 6-12 weeks and sometimes for the rest of the rat’s life.


Most Useful Antibiotics

I have found the most useful antibiotics for rats to be amoxicillin, doxycycline and enrofloxacin (Baytril).  For the past 10 years or so I have hardly used anything else.  I find that respiratory symptoms that don’t respond to these antibiotics are usually caused by congestive heart failure.



Amoxicillin is a broad spectrum antibiotic in the penicillin family. It is bacteriocidal. Although it is not effective against Mycoplasma, it is the best choice for all other bacterial infections in rats, especially abscesses, and the first antibiotic I always recommend trying. Even if a rat is on doxycycline or enrofloxacin for mycoplasma, if he develops symptoms of a secondary infection (see page 24), he should be put on amoxicillin in addition to the other antibiotic. Amoxicillin also helps Baytril work more effectively for urinary infections in rats.


Amoxicillin is one of the only antibiotics that is perfectly safe to give to pregnant and nursing mothers and babies of any age. (Another is cefadroxil, and cephalexin can be given to nursing mothers as it does not enter the milk.)


Amoxicillin has a wide dose range of 22-110 mg/kg (10-50 mg/lb) BID1, with 22 mg/kg (10 mg/lb) the standard dose. Higher doses can be tried in severe cases, or if the lower dose doesn’t seem to be working well. It should be given for at least 2 weeks after all the symptoms are gone, but can be used long-term without problems in most rats.


Amoxicillin only tends to cause diarrhea in a few individual rats. Mild diarrhea can be treated with probiotics, but if it is severe, stop the amoxicillin as soon as possible. 


The most common brand prescribed by veterinarians is Amoxi-drops, a bubblegum-flavored liquid of which the normal  dose is 0.44 ml/kg (0.2 ml/lb). But amoxicillin capsules can also be used and mixed into a liquid at home, and are a lot cheaper. Amoxicillin tastes okay to most rats and so is usually no problem to give in any form. An occasional rat will hate the taste.


Amoxicillin usually comes in a 250 mg capsule, which contains 25 1-lb. doses. To mix it, I suggest putting one 250 mg amoxicillin capsule in 7.5 ml of flavoring. Then the dose is   0.3 ml/lb, the dose for a half-pound rat is 0.15 ml and the dose for a 1¼-lb rat is 0.4 ml. For a tiny baby, give one drop. For a 500 mg capsule, use double the amount of flavoring. Amoxicillin capsules are good for years after their expiration date, and all amoxi, whether for fish, dogs or humans, is the same.


For rats who won’t take amoxicillin willingly, you can make the dose 0.1 ml/lb so it can be easily forced, by mixing one 250 mg capsule with only 2.5 ml of flavoring.


Note that amoxicillin powder does not dissolve in the flavoring and will sink to the bottom. Before taking out a dose, you must stir the mixture well with the syringe, which works better than shaking it, to get the powder in suspension. When refrigerated, the mixture will be good for 2 weeks.


Amoxicillin is available over the counter for fish.  You can order it from and also Jedd’s Pigeon Supply and Drs. Foster and Smith (see sources below.)


Other antibiotics in the Penicillin family:

ampicillin—Can be used instead of amoxicillin, but is not as well absorbed, so you must give double the dose.  Do not use with atenolol. 20 mg/lb BID for at least 2-3 weeks.  Taste okay.

amoxicillin trihydrate/clavulanate^—Effective for some bacteria that are resistant to amoxicillin.  Good for skin infections and abscesses. Some individuals are sensitive to the clavulanate ingredient.  10 mg/lb BID for 2-3 weeks. Brands: Clavamox, Augmentin. Most rats like it.


NOTE:  Some vets won’t prescribe amoxicillin for rats because they learn in vet school that amoxicillin can kill hamsters or guinea pigs, so they sometimes generalize this to all rodents.  Here are some references for vets 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 are essentially the same)


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.”


Blackwell’s Five-Minute Veterinary Consult: Small Mammals, Second Edition, Barbara L. Oblesbee. 2011 John Wiley & Sons, Inc. page 588, “amoxicillin/clavulanic acid (12.5-15 mg/kg PO q12h) may also be used.”



Doxycycline is related to tetracycline but is absorbed better and does not bind to minerals as much.  Doxy tends to work well against Mycoplasma in rats, but in rats is not good for much else. It is bacteriostatic.  This is the second antibiotic I recommend trying for respiratory symptoms in rats after amoxicillin.  It often works well together with enrofloxacin.  It should not be used in pregnant or nursing moms.  It can increase the side effects of digoxin, so enrofloxacin is better for rats on digoxin.


Doxycycline is one of the few medications that can become dangerous after its expiration date. It can change chemically and become toxic to the kidneys, so must be thrown out after its expiration date.


The most common brand prescribed by vets is Vibramycin, a flavored liquid, but you can also buy it yourself.  Doxycycline is available over the counter for fish and birds.


Doxycycline comes in either a liquid, or 100 mg capsules or packets, which can be mixed into a liquid.  100 mg contains 40 1-lb doses.  I normally recommend making the dose 0.3 ml/lb, so to do this, you mix one capsule with 12 ml of flavoring. (40 X 0.3 = 12 ml)  I recommend mixing it with either slightly diluted strawberry syrup, or almond milk flavoured with strawberry syrup.  Store it in the refrigerator. It will be good for at least 2 weeks.


The best option for doxycycline now is probably to order Doxysyrup or Doxyvet Liquid 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. I have heard from several rat owners that this liquid is not as palatable as the Doxysyrup, but it can be diluted with yummier liquid or mixed with food. 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 might also want to search on eBay or Amazon to look for other sources of doxycycline. Be sure to get either capsules or powder packets, not loose powder, and look carefully at how much you will get for the cost, because some vendors charge a lot of money.


Most rats don’t mind the taste of doxy, but some absolutely hate it and will fight against taking it.  In this case, it is usually best to use enrofloxacin (Baytril) instead.


At Jedd’s 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. Some rats don’t like the flavor but it can be diluted with tastier liquid.


The usual dose of doxycycline is 2.5 mg/lb BID1 ,12  but this can be doubled if it doesn’t seem to be working well.  Because it is used in rats mainly for Mycoplasma, it should be given for a minimum of 6 weeks at a time, and is safe for very long term use. I recommend older rats be put on a treatment for myco, either doxy or Baytril, for the rest of their lives.


If you have a rat who refuses to take the doxy voluntarily, and you need to force it, you can make the dose only 0.1 ml/lb. If you put only 0.1 ml of liquid in the back of a rat’s mouth, it is too small for them to spit out. In this case you can mix the capsule with only 4 ml of flavouring, making the 1-lb dose only 0.1 ml.  However, in this case, it is better to switch to Baytril. Usually, a rat who hates doxy will take Baytril okay, and vice versa.


Baytril (generic name: enrofloxacin)

Enrofloxacin is a broad spectrum antibiotic in the fluoroquinolone family.  It is bacteriocidal.  It is particularly good for Mycoplasma.  It can also be good for urinary infections when used along with amoxicillin.  It can safely be used very long term in rats (ie. 2 years!) Other brand names are usually similar to enrofloxacin, ie. Enrofloxin.


Enrofloxacin can be combined with doxycycline, penicillins, cephalosporins or gentamicin.  Do not use it with chloremphenicol.  It can interfere with the metabolism of bronchdilators, so doxycycline is better to use for rats on a bronchodilator.


The brand usually prescribed by vets is Baytril. The injectable form is usually 2.25% (22.5 mg/ml). Vets will sometimes want to give Baytril by injection, but it is highly caustic: DO NOT give Baytril by IM injection and only SQ when absolutely necessary as SQ injections can cause severe skin ulcers which take a very long time to heal.  I know of two rats who bled to death after scratching these ulcers! 


Some vets grind Baytril tablets and mix them in a liquid flavoring.  These preparations should probably be refrigerated. The injectable liquid, which can be given orally, or 10% oral liquid should NOT be refrigerated because it will crystalize.


The recommended dose of enrofloxacin for rats is 10 mg/lb BID4 for at least 6 weeks or long term.  A generic 10% oral liquid (100 mg/ml) is available inexpensively from pigeon supply companies (see sources below.)  The dose for the 10% liquid is 0.1 ml/lb BID.


Clear liquid Baytril, either injectable or oral, tastes pretty bad and needs to be mixed with more flavouring than most other medicines.  I don’t recommend

mixing up a lot of it ahead of time as that may affect its potency. 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. 


If you want to mix some of the Baytril up ahead of time, you can mix 0.5 ml of the 10% liquid enrofloxacin with 4.5 ml of flavouring. The 1-lb dose is then 1 ml.


Other Antibiotics

Although amoxicillin, doxycycline, and enrofloxacin will take care of most infections in rats, occasionally another antibiotic will be necessary. I highly recommend my Rat Health Care booklet as a reference.


Sources for Antibiotics

Some antibiotics can be purchased over the counter for different animals: amoxicillin and ampicillin for aquarium fish;  doxycycline and enrofloxacin for birds. Prescription drugs can be purchased either from your vet, a human pharmacy (often cheaper), or a mail order catalog. 


When ordering an antibiotic by mail order, be sure to specify if you want capsules, packets, or liquid, or you might get loose powder or tablets instead.


Here are some sources:


Jedds Pigeon Supplies , 800-659-5928   *My preferred source

for liquid doxy and 10% liquid enrofloxacin. Also amoxi capsules. Orders can be made by phone. Doxysyrup is 10 mg/ml, so the normal dose is 0.25 ml/lb twice a day. Doxyvet Liquid is 50 mg/ml, and more economical. The normal dose is 0.05 ml/lb twice a day. It can be diluted with tastier liquid. *My preferred source for amoxi capsules for fish  10% liquid enrofloxacin, doxy  10% liquid enrofloxacin, doxy


Doctors Foster & Smith, 800-826-7206  amoxi capsules for fish

A Note About Doses
I have not included liquid doses for all medications because the dose will vary with the concentration of the liquid. Here is how you convert a dose in mg to a dose in ml. Find the concentration of the medication, which will be in mg/ml. Divide this number by the dose in mg. Divide the results into 1. For example, if the concentration is 50 mg/ml, and the dose you want is 10 mg, you need to divide 50 by 10. This gives you the number of doses in one ml, in this case, 5. Dividing 5 into 1 gives you the dose in ml, in this case 0.2 ml. (One ml is exactly the same as one cc.)

To determine how many doses in a tablet or capsule, divide the strength of the pill by the required dose. For example, if the pill contains 50 mg and the dose is 2 mg, you divide 50 by 2, and you find that the pill contains 25 doses. If you need help figuring out doses, just give me a call.


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