Certain Medications can be a double-edged sword for pets: While medications may provide relief – they can also cause adverse effects that do more harm than good.

Even the smallest treatments, such as deworming, can trigger intolerance in pets, leading to bothersome yet benign symptoms such as: Itching or potentially life-threatening hypersensitivity reactions like anaphylactic shock, which can result in acute circulatory failure in dogs.

It is fortunate that such an extreme allergic reaction is rare in pets.


Understanding Drug Intolerances in Dogs

Definition:

A “Drug Intolerance” in dogs is a condition where a Dog’s Body cannot tolerate a particular medication.

Drug Intolerance occurs when a dog’s immune system overreacts to a medication, or when a dog’s body cannot properly metabolize or eliminate the Active Ingredient or Additives of a medication.

Some drugs can cause an immediate release of neurotransmitters, such as histamine, in dogs with a predisposition to them.

This results in an “Allergy-Like Reaction“. However, IgE antibodies are not involved. Instead, an allergic reaction of the immediate type is imitated without an actual allergy present.

Such reactions are also called pseudoallergic reactions. Pseudoallergic reactions occur without prior sensitization, i.e., they can occur on first contact with the active substance.


Drug Intolerances, Side Effects and Allergic Reactions.

Drug intolerances, side effects, and allergic reactions are all adverse reactions that can occur in dogs after taking a medication. However, there are important differences between these reactions.

Drug Intolerance

A drug intolerance occurs when a dog’s body cannot tolerate a medication. This can be due to a variety of factors – such as an inability to properly metabolize or eliminate the medication or a hypersensitivity to the drug.

The Symptoms of drug intolerance can range from mild to severe and may include nausea, vomiting, diarrhea, lethargy, loss of appetite, or changes in the Dogs behavior!

Examples for a Drug Intolerance in Dogs:

  1. Ivermectin: Ivermectin is an antiparasitic medication that is commonly used to treat heartworm disease in dogs. Some dogs – particularly those with the MDR1 gene mutation, can be intolerant to this Ivermectin . Dogs that are intolerant to Ivermectin may experience symptoms such as lethargy, vomiting, diarrhea, or seizures.
  2. Acepromazine: Acepromazine is a medication commonly used as a sedative and as anti-anxiety agent in dogs. Some dogs may be intolerant to this medication and may experience symptoms such as low blood pressure, difficulty breathing, or seizures.
  3. Chemotherapy Drugs: Chemotherapy drugs are used to treat cancer in dogs, but they can also cause drug intolerances. Dogs that are intolerant to chemotherapy drugs may experience symptoms such as vomiting, diarrhea, lethargy, or loss of appetite.
  4. Antibiotics: Antibiotics are commonly used to treat bacterial infections in dogs, but some dogs may be intolerant to some Antibiotics (especially Sulfonamide Antibiotics) .

Side Effects

Side effects are an expected and predictable outcome of a medication and can occur even when the medication is properly administered. They are typically mild and non-life-threatening, and can include symptoms such as nausea, vomiting, or diarrhea.

Side effects can occur in dogs that are not intolerant to the medication and are a result of the medication’s mechanism of action.

Examples for Side effects in Medications for Dogs

  1. Sedation: Some medications, such as benzodiazepines, may cause sedation in dogs. This is a side effect that does not indicate drug intolerance and is typically not life-threatening.
  2. Dry mouth: Medications, such as tricyclic antidepressants, will often cause dry mouth in dogs – a typical side effect.
  3. Changes in Blood Pressure: Medications, such as alpha-adrenergic agonists, may cause changes in blood pressure in dogs.
  4. Increased Appetite: Corticosteroids, can increase appetite in dogs
  5. Painkillers: Some painkillers such as aspirin, ibuprofen and diclofenac can cause stomach ulcers, and long-term use of cortisone promotes weight gain, water retention and hair loss.
    These Medications can also weaken the immune system if used long-term – Some may cause diabetes and high blood pressure.

Allergic Reactions

Allergic reactions occur when a dog’s immune system overreacts to a medication, and they can be life-threatening. Symptoms of an allergic reaction can include hives, facial swelling, difficulty breathing, or anaphylaxis.

Allergic reactions are typically immediate and can occur even with a small dose of a medication. Unlike drug intolerances, allergic reactions involve the immune system.

Examples for Allergic Reactions in Medications for Dogs

  1. Anaphylaxis: Anaphylaxis is a severe and life-threatening allergic reaction that can occur after exposure to an allergen, including medications. Symptoms can include difficulty breathing, swelling of the face and throat, vomiting, diarrhea, or even collapse.
  2. Hives: Hives are a common allergic-reaction that may occur after exposure to an allergen, also medications. Symptoms can include raised bumps or welts on the skin that are itchy or painful.
  3. Facial swelling: Facial swelling is another common allergic reaction that can occur after exposure to an allergen, including medications. Symptoms can include swelling of the face, lips, or tongue.
  4. Pruritus: Pruritus, or itching, is a common allergic reaction that can occur after exposure to an allergens. Symptoms can include scratching, biting, or licking at the skin.
  5. Gastrointestinal upset: Gastrointestinal upset, such as vomiting or diarrhea, can be a symptom of an allergic reaction to a medication in some dogs.

Note:

Pet owners should understand the differences between drug intolerances in Dogs, Side effects, and Allergic Reactions, as they may require different treatment approaches.

If a dog is experiencing an adverse reaction to a medication, it’s important to contact your VET immediately for advice and treatment.


Drug Cross Reactions

Cross-reaction means that a drug reaction occurs not only with a very specific active substance, but also with other active substances that are structurally related or have similar properties.

In allergic reactions, a dog’s immune system may react to different groups of substances that are structurally similar (for example, different penicillins or even penicillins and cephalosporins).

Cross-reactions also occur in intolerance reactions, namely when active substances have a similar mechanism of action (for example, different non-steroidal anti-inflammatory drugs).

Drug Cross reactions

Side effects of veterinary drugs must be distinguished from intolerance reactions and Allergic Reactions. The combination of different medicines can also cause them.

If you want to avoid interactions between different remedies, it is essential to inform the veterinarian about all the animal’s medicines- including natural remedies.

Unfortunately, even commonly prescribed preparations are not free of side effects.


Signs and Symptoms of Drug Intolerances

It’s not always easy to differentiate between drug intolerances, side effects, and allergic reactions in dogs because they can have overlapping symptoms.

Dog with allergy

A dog that experiences gastrointestinal upset after taking a medication may be experiencing a side effect, a drug intolerance, or an allergic reaction.

Similarly, a dog that develops a skin rash after taking a special medication may be experiencing a side effect, a drug intolerance, or an allergic reaction.

Here are some signs and symptoms of Drug Intolerances in dogs:

  1. Gastrointestinal Upset: Dogs that are intolerant to a medication may experience symptoms such as vomiting, diarrhea, or loss of appetite.
  2. Lethargy: Dogs that are intolerant to a special drug may appear more tired than usual or have less energy.
  3. Behavioral Changes: Dogs that are intolerant to medication may exhibit behavioral changes, such as increased anxiety or restlessness.
  4. Changes in Urine or Stool: Dogs intolerant to a medication may have changes in the color or consistency of their urine or stool.
  5. Difficulty Breathing: Dogs that are intolerant a special medication may have difficulty breathing or appear to be short of breath.
  6. Skin Reactions: Dogs that are intolerant to a medication may develop skin reactions, such as rashes or hives – what also can happen in Drug Allergies!

Note:

The differences between these types of adverse reactions can be subtle and may require additional testing or evaluation to determine the underlying cause.

A veterinarian may perform blood tests, skin tests, or other diagnostic procedures to determine whether a dog is experiencing a drug intolerance or an allergic reaction.


Examples of Common Medications that may Cause Drug Intolerances in Gogs.

In principle, any drug can cause an allergic reaction. However, a few widely used drugs are responsible for 90 percent of all reactions.

The most common triggers of drug intolerance include:

  • Antibiotics, most commonly penicillins, cephalosporins and sulfonamides.
  • Painkillers and rheumatism medicines
  • Anti-epileptic drugs
  • Psychotropic drugs such as antidepressants and neuroleptics
  • X-ray contrast media
  • Local anesthetics
  • Antihypertensives such as ACE inhibitors

Here are some examples of common medications that may cause drug intolerances in dogs:

  1. Nonsteroidal anti-inflammatory drugs (NSAIDs): NSAIDs are commonly used to treat pain and inflammation in dogs, but some dogs may be intolerant to these medications. Dogs that are intolerant to NSAIDs may experience symptoms such as vomiting, diarrhea, loss of appetite, or lethargy.
  2. Ivermectin: Ivermectin is an antiparasitic medication that is commonly used to treat heartworm disease in dogs. However, some dogs, particularly those with the MDR1 gene mutation, may be intolerant to this medication. Dogs that are intolerant to ivermectin may experience symptoms such as lethargy, vomiting, diarrhea, or seizures.
  3. Chemotherapy Drugs: Chemotherapy drugs are used to treat cancer in dogs, but they can also cause drug intolerances. Dogs that are intolerant to chemotherapy drugs may experience symptoms such as vomiting, diarrhea, lethargy, or loss of appetite.
  4. Sulfonamides: Sulfonamides are a class of antibiotics commonly used to treat bacterial infections in dogs, but some dogs may be intolerant to these medications. Dogs that are intolerant to sulfonamides may experience symptoms such as vomiting, diarrhea, or loss of appetite.
  5. Phenobarbital: Phenobarbital is a medication commonly used to treat seizures in dogs, but some dogs may be intolerant to this medication. Dogs that are intolerant to phenobarbital may experience symptoms such as lethargy, weakness, or loss of coordination.
  6. Salicylate Intolerance: Also Salicylate Intolerance is another example of a drug intolerance that can occur in dogs even this is very rare. Salicylates are a class of medications that are used to treat pain and inflammation, but some dogs may be intolerant to these medications.

Diagnosis and Treatment of Drug Intolerances In Dogs

Diagnosing “Drug Intolerances in Dogs” can be challenging because the symptoms of drug intolerances can overlap with the symptoms of other adverse drug reactions, such as side effects or allergic reactions. However, veterinarians may use a variety of tools and tests to diagnose drug intolerances, including:

  1. Physical examination: Veterinarians will perform a thorough physical examination of the dog to identify any changes in behavior, vital signs, or physical appearance that may indicate a drug intolerance.
  2. Medical history: Veterinarians will review the dog’s medical history, including any medications or supplements the dog has been taking, to identify any potential drug intolerances.
  3. Blood tests: Blood tests can be used to evaluate the dog’s liver and kidney function, which can be affected by some medications.
  4. Skin tests: Skin tests can be used to identify allergic reactions to medications, which can sometimes be mistaken for drug intolerances.

If a drug intolerance is suspected, you VET may recommend stopping the medication and switching to an alternative treatment. In some cases, the dog may need to be hospitalized for supportive care, such as intravenous fluids or oxygen therapy, to manage the symptoms of the drug intolerance.


Preventing Drug Intolerances

Here are some tips and advice on how pet owners can prevent drug intolerances from occurring in their dogs:

  1. Follow dosage instructions: Pet owners should always follow their veterinarian’s instructions when administering medications to their dogs. Giving too much medication or administering it too frequently can increase the risk of adverse reactions, including drug intolerances.
  2. Monitor for adverse reactions: Pet owners should monitor their dog for any adverse reactions to medications and report any symptoms immediately to their veterinarian. This includes symptoms such as vomiting, diarrhea, lethargy, or changes in behavior.
  3. Regular check-ups: Regular check-ups with the veterinarian can help identify any potential drug intolerances or other adverse reactions before they become severe. Pet owners should schedule regular appointments with their veterinarian to monitor their dog’s overall health and to discuss any concerns about medication use.
  4. Avoid self-medicating: Pet owners should avoid self-medicating their dogs and should only give medications that have been prescribed by their veterinarian. Over-the-counter medications and supplements can interact with prescription medications and increase the risk of adverse reactions.
  5. Genetic testing: In some cases, genetic testing can be performed to identify potential drug intolerances. For example, dogs with the MDR1 gene mutation may be intolerant to certain medications, including ivermectin.

By following these tips and working closely with their veterinarian, pet owners can help prevent drug intolerances from occurring in their dogs and ensure that their dog receives safe and effective treatment.


Summary

Drug intolerances are a type of adverse reaction to medications that can occur in dogs. They are different from side effects and allergic reactions, but can have overlapping symptoms.

Some common Medications that can cause drug intolerances in dogs include NSAIDs, chemotherapy drugs, antibiotics, and ivermectin. Salicylate intolerance is another example of a drug intolerance that can occur in dogs.

Diagnosing drug intolerances can be challenging, but a thorough evaluation by a VET can help identify the underlying cause. Treatment options include stopping the medication and switching to an alternative.

Prevention is key, and pet owners can help prevent drug intolerances by following dosage instructions, monitoring for adverse reactions, and scheduling regular check-ups with their VET.


Sources:

  1. Hansen, S. R. (2018). Adverse Drug Reactions in Dogs and Cats. Veterinary Clinics of North America: Small Animal Practice, 48(4), 745-763. doi: 10.1016/j.cvsm.2018.02.002

https://www.sciencedirect.com/science/article/pii/S019556161830017X

  1. KuKanich, B., & Papich, M. G. (2015). Pharmacokinetics and adverse effects of H1-receptor antagonists in dogs and cats. Journal of Veterinary Pharmacology and Therapeutics, 38(5), 441-463. doi: 10.1111/jvp.12224

https://onlinelibrary.wiley.com/doi/abs/10.1111/jvp.12224

  1. Mealey, K. L., & Meurs, K. M. (2008). Breed distribution of the ABCB1-1Delta (multidrug sensitivity) polymorphism among dogs undergoing ABCB1 genotyping. Journal of the American Veterinary Medical Association, 233(6), 921-924. doi: 10.2460/javma.233.6.921
  2. Fossler, C. P., & Mavromatis, K. (2017). Adverse drug reactions: Types and treatment options. The Veterinary Clinics of North America. Small Animal Practice, 47(5), 1027-1042. https://doi.org/10.1016/j.cvsm.2017.04.006
  3. Rieder, M. J. (2021). Overview of adverse drug reactions. UpToDate. https://www.uptodate.com/contents/overview-of-adverse-drug-reactions
  4. Trepanier, L. A. (2013). Adverse drug reactions. In Small Animal Clinical Pharmacology (2nd ed., pp. 39-44). Elsevier Health Sciences.

Trepanier, L. A. (2013). Adverse drug reactions. In Small Animal Clinical Pharmacology (2nd ed., pp. 39-44). Elsevier Health Sciences.


Dr-Orika-Mosquera-Lopez

Dr. Orika Mosquera

Hello, I am Dr. Orika Mosquera Lopez graduated from the free university of colombia sectional Barranquilla as a doctor and surgeon. I work as a General Practitioner with Experience in the Emergency Department, Hospitalization and External Consultation. I love pets, i have 2 cats, Bagheera and Nhala and one Yorkshire Terrier called Princess. I care a lot about the well-being of my animals

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