Metronidazole (Flagyl) Toxicity in Dogs

Although there have been serious side effects reported in some dogs, if it is prescribed, then the veterinarian believes your dog will benefit from metronidazole. You should always talk to the veterinarian about any side effects or complications before administering them to your pet. The chance of metronidazole toxicity may be low, but it is possible that it could affect your dog in a bad way. There are serious implications with metronidazole, such as neurological injury and hepatotoxicity (liver damage).

Metronidazole, or Flagyl, is an antibiotic and antiprotozoal drug that is used in treating many kinds of infections such as diarrheal disorders, giardia, inflammatory bowel disease, and dental infections to name a few. Because it is able to pass through bone, it is often given for oral infections and is a commonly used drug for inflammatory disorders of the large intestine. However, this drug is not approved by the FDA for use in animals, so if your veterinarian prescribes it you should talk about this decision carefully.

The symptoms of metronidazole toxicity may be immediate, could take several hours, or can even take 7-10 days to show up, depending on the dosage and the cause. Allergic reaction is usually immediate, but with an accidental overdose it may be several days before your dog starts to show any signs of complications. Signs can include:

• Drooling
• Gagging
• Smacking lips
• Pawing at the mouth
• Cough
• Sneezing
• Runny nose
• Extreme lethargy
• Weakness
• Nausea
• Vomiting
• Appetite loss
• Fever
• Chills
• Hives
• Dizziness
• Confusion
• Agitation
• Sores inside the mouth or on the lips
• Watery or bloody diarrhea
• Loss of balance or coordination
• Swelling of the face, lips, tongue, or throat
• Inability to walk
• Irregular heart rate
• Difficulty breathing
• Liver damage (yellowing of the eyes and skin, appetite loss, fever, diarrhea, fluid retention)
• Seizures
• Death

 Types

• Overdose occurs when the wrong dose or a double dose is given or if your dog gets into the medication
• A bad reaction can be from an allergic reaction or drug sensitivity
• Drug interaction happens when you give your dog metronidazole with another drug that should not be mixed; some of those drugs are warfarin, coumarin, cimetidine, sedatives, phenobarbital, and phenytoin

• Accidental overdose
• Allergy
• Drug interaction

Try to bring your medical and shot records and be prepared to explain the reason for your visit in detail. Also, be sure to bring the metronidazole with you and tell the veterinarian if you have given any other medications besides the metronidazole. The veterinarian will need to perform a detailed physical examination, which includes weight, body temperature, reflexes, pupil reaction time, coat and skin condition, breath sounds, heart and respiratory rate, blood pressure, and oxygen level. Some important tests for verifying metronidazole toxicity are a blood test and urine analysis. As signs are often neurological, we may also advise spinal taps and an MRI or CT scan. Your dog will be anesthetized for these procedures for safety. The spinal tap is done by inserting a thin needle into the spinal cord at the back of the neck or lower back and collecting spinal fluid into a tube to be analyzed. The spinal tap will likely show increased protein.

An MRI (magnetic resonance imaging) will be done to check the brain function, which may find hemorrhaging and degeneration of the cerebellum. Other tests are usually found to be normal, but the veterinarian will want to do a blood count and serum analysis to check for underlying illness or side effects. In addition, radiographs (x-rays), CT scan, and an ultrasound may be done for further inspection.

Treating metronidazole toxicity is done by stopping the medication and treating the symptoms as they occur.

Fluid Therapy

Your dog should already be receiving intravenous (IV) fluids from the earlier procedure. The veterinarian will likely continue the fluids and add nutrients and electrolytes as needed. This will keep your pet from getting dehydrated and flush the kidneys as well.

Medication

The medications your dog is given depends on the symptoms and test results, but they will likely administer diazepam right away. This drug is able to alleviate vestibular dysfunction in animals and shortens the recovery time. However, the average length of recovery time is 12-16 days and may be as long as three weeks.

Hospitalization

The veterinarian will likely suggest your dog be hospitalized for at least 24 hours for observation and supplemental treatment. The length of your dog’s stay depends on the severity of the symptoms and how well your pet responds to treatment.

Recovery from metronidazole toxicity is a long process and depends on the amount of time your dog was on the medication and how much was given or accidentally ingested. Usually, all of the side effects can be reversed and your dog should have no lasting complications as long as your pet received treatment from a veterinary professional. Be sure to follow the veterinarian’s instructions and return for your pet’s follow up appointment for evaluation.

Paying to treat metronidazole toxicity out of pocket can be a major financial burden. Fortunately, most pet insurance companies reimburse claims within 3 days, putting 90% of the bill back in your pocket. In the market for pet insurance? Compare leading pet insurance companies to find the right plan for your pet.