Antibiotic side effects in dogs

There are a myriad of conditions that would require dogs to be treated with antibiotics, including bladder infections, ear infections and flesh wounds, just to name a few.

If you suspect that your dog has an infection that needs to be treated with antibiotics, it is crucial to get a proper diagnosis from your veterinarian to confirm the course of treatment. Your vet will culture the type of bacteria to determine the right antibiotic to administer. Any antibiotic administered to your dog poses potential side effects. The adverse reactions and potential side effects that stem from antibiotic use can be summarised in three predominant categories: increased drug resistance, allergic reactions/toxicity and diminishing your dog's "good" bacteria.

Drug Resistance

Drug resistance is a serious problem in both human and veterinary medicines. This occurs when bacteria becomes resistant to the antibiotics to which they have been exposed. The bacteria develop means to fight off the antibiotic and survive. These new, antibiotic-resistant bacteria can infect others who will then develop antibiotic-resistant strains of the infection. If your dog does not finish an entire course of medication to completely eradicate an infection, the bacteria can begin to develop resistance.

Toxic Effects/Allergic Reactions

Toxic effects include possible damage to important organs and cells (for example, the antibiotic aminoglycoside can be toxic to kidney cells). Using proper dosing as guided by your veterinarian is crucial to minimising the potentially toxic affects of medications to your dog. Allergic reactions can be serious and even life-threatening. If you see any warning signs like sudden vomiting, diarrhoea, seizure, shock or coma, seek emergency care immediately. Facial swelling, rapid heart beat, cold limbs and coma are additional symptoms of anaphylaxis, a severe allergic reaction.

Killing "Good" Bacteria

Additionally, antibiotics often kill the "good" bacteria and flora in the gastrointestinal tract, leaving your dog more susceptible to other pathogens and new infections. Introducing probiotics like acidophilus or lactobacillus can help replenish your dog's store of healthy bacteria and improve symptoms of gastrointestinal distress. If you regularly give your dog probiotics, administering staggered doses throughout the day of twice the normal amount will maximise their benefits.

Commonly Prescribed Antibiotics and Possible Side Effects

Aminoglycosides can cause hearing loss, nerve damage, facial swelling and kidney damage; Neomycin, Amikacin and Gentamycin can cause kidney damage (if injected); Penicillins can cause rash, allergic reaction, anaemia, low white blood cell count, fever and gastrointestinal distress; Tetracycline can cause hair loss, light sensitivity, discoloured teeth, gastrointestinal upset, and kidney or liver disease; Erythromycin can cause low white blood cell count, bloody urine, diarrhoea, vomiting, liver damage and neurological problems; Clindamycin can cause gastrointestinal upset; Cephalosporins can cause diarrhoea, gastrointestinal problems, allergic reaction and cross-reaction with penicillin; Sulfa medications can cause anaemia, fever, vomiting, nausea, liver/kidney irritation and leucopenia; Enrofloxacin can damage cartilage in dogs that are still growing, as well as bring on disease of the gastrointestinal tract and urine crystals; Rifampin can cause gastrointestinal distress, discoloured urine and tears, and liver damage; Metronidazole can cause lower white blood cell counts, bloody urine, diarrhoea, vomiting and neurological problems.


There are some websites on the Internet that advocate treating your dog at home using human antibiotics or non-prescription antibiotics like those used for treating infections in fish. This increases your dog's risk of experiencing side effects or adverse reactions, and could be detrimental to its long-term health. Always consult your veterinarian before beginning any medication.