An adverse drug reaction is a term used to describe when dogs have an undesired response to a medicinal product. This includes anything from tablets and injections to medicated shampoos or ear cleaners. There are many different types of adverse reactions. Adverse drug reactions can be difficult to diagnose because the symptoms are often vague and can result from various causes.

It's important to be aware that vets select and administer medications with precision, based on a wealth of clinical studies and evidence to determine the appropriate dosage and treatment. Any dog can develop a reaction to any drug. Adverse drug reactions can vary from very mild to severe, including death. Most drug reactions only cause mild symptoms; severe reactions are very uncommon.

What to do if your dog is showing signs of an adverse drug reaction

It’s best to speak to a vet as soon as possible

• Let the vet know of any symptoms your dog is showing

• Determine if your dog got a larger dose than recommended at home

• Stay calm and avoid asking for advice on internet forums; these can be full of misinformation.

Most adverse drug reactions are mild and can be monitored or treated at home. Our Joii vets are available 24 hours a day for advice. Call us now if you have any questions.

Most common causes of adverse drug reactions in dogs

The most common reported reactions are those from:

• Vaccinations

• Antimicrobial medications, such as antibiotics

• Non steroidal anti-inflammatory medications (NSAIDs)

• Parasite preventatives

• Anaesthetic agents

These are the most commonly used medications in veterinary medicine, so it’s likely that this is why we see more reactions reported, rather than these being more risky.

When to worry about an adverse drug reaction in dogs

An emergency exam will be needed if your dog:

• Has severe vomiting and diarrhoea

• Is showing any neurological signs, such as incoordination or seizures

• Has breathing problems

Call us and speak to one of our Joii vets if your dog:

• Has mild vomiting or diarrhoea

• Has itchy or red skin

Tips on how to prevent adverse drug reactions in dogs

• Always stick to the dose that your vet has prescribed. If the dose is not clear, double-check before giving it to your dog.

• If you miss a dose or overdose by accident, always check with your vet before giving any further medication.

• Never give your dog human medications, unless specifically advised to do so by your vet.

• If your dog is on long-term medication, make sure to attend regular check-ups with your vet. Regular blood and urine tests are advised for certain medications.

How to know if your dog is having an adverse drug reaction

Adverse drug reactions are difficult to diagnose, as the symptoms tend to be quite vague and can have many different causes. Symptoms (especially severe ones) will usually appear within a few hours but can be up to 2-3 days later. The most common symptoms of drug reactions include:

• Vomiting

• Diarrhoea

• Lethargy

• Reduced or increased appetite

• Increased thirst

• Skin reactions: itching, redness, hives and hair loss

• Drooling

• Sedation

Severe allergic reactions are rare but life-threatening.

Symptoms include:

• Difficulty breathing

• Red or blue gums

• Seizures

• Collapse

How to help at home if your dog has an adverse drug reaction

Most cases of mild reactions can be treated at home:

• Remove any products applied to the skin by washing thoroughly

• Feeding small meals of bland food can help dogs with tummy upsets

• Heating the food slightly can help with palatability

• Allow rest and monitor for any new symptoms

• Using a buster collar for itchy dogs can help prevent self-trauma

Treatment for adverse drug reactions in dogs

The treatment approach depends on the severity of the reaction. Typically, it involves removing any remaining drug from the body and providing symptomatic relief.

This may include:

• Emergency treatment for anaphylactic reactions: hospitalisation, fluids via a drip, and emergency medications.

• Anti-seizure medication

• Antihistamines

• Corticosteroids

• Activated charcoal: to reduce further absorption of the drug

• Induced vomiting, if caught early

• Antidotes: if available, though these are not common in vet medicine

Are some dogs more at risk of adverse drug reactions?

• Age can have an effect on how the body processes certain medications. Both very young and elderly dogs may be more likely to have reactions to medications.

• Dogs with liver disease because that's where drugs are processed in the body.

• Dogs with kidney disease because that's where drugs are eliminated.

• Dogs with heart disease may also have an increased risk.

• Dogs with allergies or atopy.

• Dogs with the MDR1 gene mutation have a higher risk of reactions to certain medications, such as ivermectin. This includes Collies, Australian Shepherds, Shetland Sheepdogs, and Old English Sheepdogs.

• If a dog has had a previous reaction to a medication, it’s likely that this will recur if the medication is used again. These further reactions can be more severe.

Other risks (less common)

• Adverse drug reactions can lead to transient problems in the liver and kidneys. These often improve once the medication is stopped.

• Another less common side effect is auto-immune disease, such as immune-mediated haemolytic anaemia.

• Stomach ulcers caused by NSAIDs and steroids.

• Lumps caused by injection reactions.

• Neurological signs, such as incoordination and seizures due to flea or tick preventatives.