Metronidazole (Flagyl) Toxicity Average Cost

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What is Metronidazole (Flagyl) Toxicity?

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.

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Symptoms of Metronidazole (Flagyl) Toxicity in Dogs

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.

  • 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


  • Overdose occurs when the wrong dose or a double dose is given or if your dog gets into the medication
  • 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

Causes of Metronidazole (Flagyl) Toxicity in Dogs

  • Accidental overdose
  • Allergy
  • Drug interaction

Diagnosis of Metronidazole (Flagyl) Toxicity in Dogs

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 height, 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 spinal tap and an MRI. Your dog will be anesthetized for both 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 functioning, 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.

Treatment of Metronidazole (Flagyl) Toxicity in Dogs

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.


The medications your dog is given depends on the symptoms and test results, but 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.


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 of Metronidazole (Flagyl) Toxicity in Dogs

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.

Metronidazole (Flagyl) Toxicity Questions and Advice from Veterinary Professionals

Border Collie
10 Years
Moderate condition
0 found helpful
Moderate condition

Has Symptoms


Medication Used


my dog bailey has a tumor on his lung,and prostate cancer,he has started having diarrhea,last time he had metronidazole he ended up having heavy breathing,i know that metronidazole has helped in the past,is there something else i can try to get his tummy back to normal

Dr. Michele King, DVM
Dr. Michele King, DVM
1402 Recommendations
Thank you for your email. WIthout examining Bailey and knowing more about his health history and status, I can't comment on what might help with his diarrhea. Since it may be related to any number of conditions, it would be best to consult with your veterinarian to assess his health, examine him, and determine what might be the best treatment for him.

i Got my dogs medication mixed up and gave him 250 mlg of metronidazole in a period of 3 days he is about 3-4 pounds, what can I do to help him since I don’t have the money yet to take him to get checked with the vet. He’s weak, can’t eat, had a seizure and has been throwing up, please help I’m desperate

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11 Years
Moderate condition
2 found helpful
Moderate condition

Has Symptoms


Medication Used

Cerenia tablets

I am giving my dog metronidazole 1/2 of a 250 mg tab twice a day. After I administer it he starts trembling. He is legtharic and not eating at all. He started to get sick Saturday night. He had a fever yesterday of 105.2 taken at the vet. Received IV with cerenia and metronidazole and fluids. Is he having a reaction to the metronidazole?

Dr. Callum Turner, DVM
Dr. Callum Turner, DVM
2985 Recommendations

Trembling, lethargy and a loss of appetite are all associated with side effects and/or toxicity with metronidazole; if you are noticing these symptoms you should return to your Veterinarian immediately for another examination and to determine if Cosmo continues with metronidazole or a move is made to another medication. Regards Dr Callum Turner DVM

My 12 lb Doxie just died from this. Vets failed to warn of issues. So sad.

I recently gave my 4 month old 5 lb toy poodle 250 mg 3 times over 2 days. He showing no signs of symptoms and is behaving normal. I'm worried and scared what should I do?

I was given the medication for my six yr old little dog. For a bacteria infection. And sent home. Two hrs later. We ruched her back to the vet. She died. Within two hrs of taking it

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Miniature Schnauzer
14 Weeks
Serious condition
0 found helpful
Serious condition

Has Symptoms

Seizures. No use of back legs

My 4 lb 10 week old mini schnauzer was given metronidazole for diarrhea. She was to take an eighth of a pill twice Dailey, however the tablets went cut evenly so I’m sure that some days she got too much. The day after I stopped giving it to her, she had mild seizures and lost use of her back legs. It has been 21 Days. She still cannot walk. She has improved, in that she can stand on her own for short periods of time and has taken several very wobbly steps. I was expecting her to be back to normal by now. Do you think she will regain use of her back legs? Wonder how long this will take?

Dr. Michele King, DVM
Dr. Michele King, DVM
1402 Recommendations
Thank you for your email. Toxicity to Metronidazole is not common, but it does occur. If you think that Sally had a reaction to that medication, it would be best to have her seen by your veterinarian, and determine that that is the cause. If she did have an adverse reaction to the drug, the signs should improve as it leaves her system, but it would be best to follow up with your veterinarian, partly so that they know what is going on, and partly so that they can give her any supportive care that she may need. I hope that she is okay!

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English Bulldog
11 Years
Moderate condition
0 found helpful
Moderate condition

Has Symptoms


Our 10 1/2 year old English bulldog Zeus had a bad bacterial infection where h was throwing up and vomited some blood. He was prescribed flagyl two days ago . Only side effects we're seeing are fatigue with some heavy breathing, some loss of balance and appetite loss. He is sleeping most of the day but the throwing up and diarrhea accidents have stopped. He is a 58 lb dog and is taking 1 1/2 pills in th morning and evening as prescribed. Do you think this dosage is too much for him ? Don't won't too overdue it Thanks. Kw

Dr. Michele King, DVM
Dr. Michele King, DVM
1402 Recommendations
I'm not sure what strength the tablets are that you are giving Zeus, and there are many sizes of those tablets available. The dose range for a dog his size would be from 263 mg to 527 mg. If the tablets that he is taking are in that dose range, it would be best to continue the prescription that your veterinarian recommended. If the loss of balance is dramatic, that may be a side effect of that medication and you should call your veterinarian to see how they want to proceed.

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2 Years
Serious condition
0 found helpful
Serious condition

My dog had severe flagyl toxicity and was hospitalized for a week. Then I took him home for 2 more weeks before he started acting normally. My question is can going through all this with the seizures, nystagmus and inability to walk, would this change his personality? He doesn't seem to be as happy go lucky as he was. Even his groomer states he's not the same dog. Will he come back to normal?

Dr. Callum Turner, DVM
Dr. Callum Turner, DVM
2985 Recommendations
The problem with issues like this is that you cannot explain this is a dog, so they their behaviour can change since they are unaware of what is happening and why; it may take some time for Oliver’s personality to come back but I cannot say whether he will ever be the same dog as before. Traumatic events whether physical, psychological or both can have a lasting effect on a dog; all you can do is offer the same love, care and attention you always have given. Regards Dr Callum Turner DVM

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