Antibiotics Allergies in Dogs

A variety of different antibiotics are prescribed to treat bacterial infection in dogs. These drugs either kill bacteria outright (bactericidal) or they make it more difficult for the bacteria to grow and reproduce (bacteriostatic). Some antibiotics are broad-spectrum, meaning they are effective for a variety of different diseases, while others are narrow-spectrum since they mainly target one type of bacteria or infection. Antibiotics fall into different classes, based on their chemical structure and the mechanism with which they target bacteria. The most common and well known are the beta-lactam antibiotics, like penicillin, which prevent bacteria from forming a cell wall. Other classes of antibiotics can affect DNA synthesis or the production of necessary proteins in certain bacteria.

Any drug has the potential for side-effects or allergic reaction. Side-effects refer to the negative effects the drug may have on the body, while allergic reaction describes an immune system response that targets the medication as a threat. While side-effects will be present to a greater or lesser degree in any dog taking the drug, allergic reactions are based on individual sensitivity to a specific medication. Unfortunately, antibiotics cause more allergic responses in dogs than any other group of drugs. Most symptoms are typical of other histamine producing allergies; dogs may develop an itchy rash, and watery eyes or nose. Swelling of the face or even the respiratory tract is possible. In rare cases, dogs can have a severe, life-threatening reaction called anaphylactic shock. This can cause collapse, difficulty breathing and even death.

Most owners won’t be aware of an allergic response until the antibiotic is prescribed to their dog. This is why it is important to watch dogs carefully anytime a new medication is started and get immediate treatment for symptoms that appear unusual or severe. All previous allergic reactions should be communicated to the veterinarian before an antibiotic is prescribed. If your dog has an allergic response to one antibiotic, it’s likely that he will experience a similar problem with other medications in the same class.

Antibiotics help to eliminate harmful bacteria and are some of the most important medications for dogs, however they are also one of the most common causes of allergic drug reaction. Symptoms range from mild rash and watery eyes, to rare, but life-threatening, anaphylaxis.

Look for these symptoms if your dog is taking an antibiotic for the first time.

• Rash (maculopapular lesions)
• Redness (erythroderma)
• Other types of skin lesion (blisters or scaling skin)
• Itchiness (pruritus)
• Incessant scratching
• Watery eyes
• Runny nose
• Swelling and hives (uticaria-angiodema)
• Purple rash caused by bleeding into the dermal tissue (purpura)
• Anaphylactic shock which is rare (vomiting, diarrhea, difficulty breathing, collapse, death)

Types

There are too many antibiotic classes to list them all. Following are some common types that could be prescribed to your dog. Penicillins and sulfonamides have the highest rates of allergic reaction.

• Beta-lactam antibiotics – group of bactericidal drugs that inhibit the formation of the cell wall including penicillin, cephalosporins, and cephamycins
• Sulfonamides (sulfa drugs) – a group of bacteriostatic drugs, one of the most common antibacterial agents prescribed to dogs because their low cost and relative effectiveness in treating typical bacterial infections; examples are sulfadiazine, sulfadimethoxine, and succinylsulfathiazole
• Tetracyclines – broad-spectrum bacteriostatic agents that get their name because of their chemical structure with four rings; Oxytetracycline, Minocycline, and Doxycycline are some examples used in dogs
• Quinolones and Fluoroquinolones – a group of bactericidal antibiotics that interfere with the bacteria’s ability to make DNA; some examples are ciprofloxacin, danofloxacin and difloxacin
• Aminoglycosides – this is a group bactericidal antibiotics that stops the production of necessary proteins in the bacteria, Gentamicin and Amikacin are two examples used in dogs
• Macrolides – bacteriostatic antibiotics that inhibit the production of bacterial protein; Azithromycin is the main example used in dogs

These are some causes and risk factors for antibiotics allergies.

• New antibiotic prescribed to your dog
• Dog develops a new allergy
• General tendency toward allergic reactions

Antibiotic allergies are typically diagnosed because owners notice an unusual response when their dog begins a new medication. Rarely, dogs could also develop a new allergy to an antibiotic which previously didn’t cause a problem. There isn’t any way to test for an antibiotics allergy without actually giving the drug to your dog. 

You should call the veterinarian if you see abnormal symptoms in your dog, especially when these correspond with the start of a new mediation. The veterinarian will be able to tell you if this is a typical side-effect, part of the original infection, or a more dangerous response. Life-threatening symptoms like collapse or difficulty breathing should be treated as an emergency.

With any drug reaction, the first important treatment is to stop taking the medication. If the reaction was mild, your dog’s symptoms will likely clear up on their own and no further treatment will be necessary. However the veterinarian may still need to prescribe another antibiotic to treat the original infection.

Creams and topical ointments may be necessary for severe rashes and skin infections. This can help them heal and reduce the chances of further infection. Affected areas may need to be clipped of hair and covered with a bandage. Antihistamines or corticosteroids could be given to reduce symptoms and make your dog more comfortable.

Anaphylactic shock will need more aggressive treatment. Immediate epinephrine injection can reduce life-threatening symptoms. Additional oxygen, intravenous fluids, blood transfusions and other emergency measure could also be necessary.

If symptoms continue after the antibiotic is discontinued, this suggests the allergic reaction was likely related to another trigger. You should discuss this with the veterinarian and research other possible causes.