Updated September 24, 2019

I just recently finished a course of antibiotics for a chronic sinus infection, and while I feel so much better because of them, side effects of the medication are lingering. As you know, our bodies are full of beneficial bacteria. When we take antibiotics for bacteria causing us illness, our levels of good bacteria take a hit, too, and often we are left with effects like gastrointestinal upset until our bodies get back in balance. My experience this go around with antibiotics got me thinking about side effects of common medications in our pets.

The two most commonly prescribed medications in veterinary medicine (besides heartworm prevention and flea/tick medications) are antibiotics and steroids, so it makes perfect sense to address those two medications today.


Let’s start with antibiotics. Even the healthiest of pets has probably been on antibiotics at one time or another. Antibiotics are used for bacterial infections, from skin infections to respiratory infections to urinary tract infections to blood and bone infections and more. If bacteria is the cause of your pet’s symptoms, antibiotics are your friend. Like other medications, they are usually covered by pet insurance. 

The most common side effect by far from the use of antibiotics is gastrointestinal upset. This includes both vomiting and diarrhea. Vomiting can sometimes be prevented by giving medication with food rather than on an empty stomach, but diarrhea is a different story. Generally, antibiotic induced diarrhea is due to the upset of the natural flora (good bacteria) in your pet’s gastrointestinal tract. Giving probiotics or yogurt with active cultures can help your pet’s stools get back to normal.

Other side effects from antibiotics are possible, depending on the particular antibiotic. Some classes of antibiotics are known to cause a condition known as dry eye in dogs, while others can cause birth defects in the fetus if given to a pregnant dog or cat. Your veterinarian or a member of her staff will probably discuss potential side effects with you before you leave the clinic with a new medication, but if she doesn’t, be sure to ask. You’ll want to know what to look out for in case an adverse reaction occurs.

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Let’s move on to steroids, which have many applications for veterinary patients. Steroids act in several ways, but veterinarians mostly rely on them for their anti-inflammatory properties. They can be used to bring down swelling or treat acute or chronic pain, and they work wonders on itchy dogs and cats. Steroids can also be used to suppress the immune system, easing the symptoms of allergies and auto-immune related illnesses like hemolytic anemia and thrombocytopenia.

The way in which steroids act on your pet’s body has a lot to do with the dose of the drug used. A low dose of steroid is perfect for an itchy dog, but a much higher dose will be needed in a pet with an autoimmune condition. The dose will also affect the level of side effects you see in your pet.

Steroids are notorious for causing side effects in pets, and sometimes owners will even refuse the medication because they don’t want to deal with them. The most common side effects we see in pets on steroids are an increase in the amount of water they drink and an increased appetite. Pets on steroids are typically ravenous, bugging their owners and whining for food every chance they get. And because they are drinking so much water, they need to go outside for potty breaks more often (and are prone to accidents if they can’t get outside). Owners often find that these side effects are more troublesome than the original symptoms!

Common side effects are just part of the package with drugs like antibiotics and steroids, and we put up with them because these drugs save our pets’ lives. From time to time, however, the side effects of your pet’s medications may be doing more harm than good. Always talk to your vet about potential side effects from medications before you go home, and keep a close eye on your pet, especially when you’re administering a new medication.

Aug 25, 2014
Pet Health

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