Metronidazole (Flagyl) Toxicity in Dogs
Written By Darlene Stott
Published: 11/26/2016Updated: 10/21/2021
Veterinary reviewed by Dr. Linda Simon, MVB MRCVS
Metronidazole (Flagyl) Toxicity in Dogs - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost
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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Metronidazole (Flagyl) Toxicity Average Cost
From 569 quotes ranging from $200 - $1,000
Average Cost
$350
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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. 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
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 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.
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.
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.
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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.
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.
Metronidazole (Flagyl) Toxicity Average Cost
From 569 quotes ranging from $200 - $1,000
Average Cost
$350
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Metronidazole (Flagyl) Toxicity Questions and Advice from Veterinary Professionals
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Mutt
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dog-age-icon
Three Years
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1 found this helpful

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1 found this helpful

My pet has the following symptoms:
Loose Bowel Movements
How long does it take to get out of their system after they took the last pill. Can it make them nauseous
July 26, 2020
Answered by Dr. Michele K. DVM
1 Recommendations
Thank you for your question. That medication does not tend to cause nausea, and if your veterinarian gave it to your dog for diarrhea, the diarrhea should be resolved by the time you finish the medication. If it is not getting better, it would be best to have a recheck with your veterinarian, as there may be something else going on. I hope that all goes well for your dog!
July 26, 2020
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Yorkie
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dog-age-icon
Eight Years
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0 found this helpful

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0 found this helpful

My pet has the following symptoms:
Panting, Won'T Settle
Took my dog to the emergency vet two days ago with bloody diarrhea. Vet prescribed metronidazole and a probiotic. Today she's panting and can't seem to settle.
July 21, 2020
Answered by Dr. Michele K. DVM
0 Recommendations
Thank you for your question. She may still be uncomfortable from her GI upset. If things are getting better with her metronidazole and probiotic, then she may just need to some time to adjust and feel better. If she is not getting better with the metronidazole and the probiotic, and she is still having problems. It would be best to have a recheck with your veterinarian, and see what is going on. I hope that all goes well for her.
July 21, 2020
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French Bulldog
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dog-age-icon
Ten Months
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3 found this helpful

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3 found this helpful

My pet has the following symptoms:
Vomiting Blood
My dog was given metronidazole for giardia this is second day on medication and has been throwing up bright red blood all night and morning
July 12, 2020
Answered by Dr. Sara O. DVM
3 Recommendations
Hello, So sorry to hear about your dog. If she is vomiting blood, I would reccomend stopping this medication for right now and see a vet as soon as possible. Vomiting blood is never a good sign that should see a vet right away. I hope your dog starts to feel better soon.
July 12, 2020
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Pit bull
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Hella
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10 Years
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3 found this helpful

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3 found this helpful

My pet has the following symptoms:
Tired
My dog Hella was vomiting a little, no temp, and wanting little food. She was a bit tired than normal but still totally responsive and active,also drinking water as normal. She was not spayed. We took her into a vet and they gave her blood tests, ultra sound, The vet said she was pre diabetic, her liver enzymes were high and they suspected a uterine infection, They said to treat her with meds prescribed then when well to book a spay. They said the meds were safe and she need to rest alot. The meds were Metronidazole 500 mgs twice daily,amoxicillin,a liver pill and a anti nausea. Hella weighed 77 lbs. During the week she drank normally, ate only when I hand fed her with little interest. She resisted the meds. We stuck with it as vet advised. All she wanted to do was sleep. On day 7 after giving meds she fell to the floor with seizures. The first vet visit was 930.00. My husband carried her into vet. At first they did not have time for her to I said she seemed to be dying. At the vet the wanted to send her to another vet for ultrasounds. Though they had said she had no tumors ect on first visit. They took blood and said her liver levels were good. The gave her iv fluids and valium. She did not stop having seizures. We made the decision to have her put to sleep. We asked if the meds did this and they pooed and pawed about it. They denied it could cause this. If I had been told the danger I this drug I would of NEVER allowed it. The second vet visit was almost 800 dollars for about 3 or 4 hours in there. I am very heartbroken and mad we were not told the dangers of this drug. I posted a bit on fb and the replied. Seizures are never fun...................She went in for a slight infection and it ended in death...I am afraid to ever trust another vet. And most assuredly will check any and all meds in future.
Aug. 28, 2018
Answered by Dr. Michele K. DVM
3 Recommendations
I"m very sorry for the loss of your Hella, that is very sad. Those medications are very commonly used, and very safe, generally. I'm not sure that the medication would have caused the seizures after 7 days of giving them, and think that something else may have caused her seizures. I hope that you will be able to trust your veterinarian in the future, and am sorry, again, for your loss.
Aug. 28, 2018
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English Bulldog
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Zues
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11 Years
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2 found this helpful

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2 found this helpful

My pet has the following symptoms:
Weakness
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
May 26, 2018
Answered by Dr. Michele K. DVM
2 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.
May 26, 2018
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toy poodle
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Fifi
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14 Years
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0 found this helpful

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0 found this helpful

My pet has the following symptoms:
Diarrhea
Fifi was my life being a recent widow. My sweet 6 lb toy poodle had diarrhea and I immediately took her to Banfield Clinic. Expensive test were given and all came out fine. After the Vet visit she was still having diarrhea and I gave her one 0.25 of Metronidazole. a few hours later she died in my arms. I can't stop crying feeling like I killed my dog - I feel like a murderer. Fifi was a senior dog but ran around the house and yard like a puppy. She was so healthy. The Vet even gave me a follow up appointment and I made her grooming appointment. I feel so guilty since I did not do my "homework" and read about this medicine before I gave it to Fifi. For sure I would not have used it and my sweet Fifi would still be part of my life.
Metronidazole (Flagyl) Toxicity Average Cost
From 569 quotes ranging from $200 - $1,000
Average Cost
$350
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