Flagyl® (Metronidazole) Dosage Calculator for Dogs
Calculate veterinary guidelines based on weight and medical condition
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Your veterinarian may prescribe Flagyl® Dosage For dogs (metronidazole) to be used as a part of your dog's treatment plan if your dog suffers from diarrhea, bacterial infection or some intestinal parasite infection. Metronidazole dosage for dogs is a widely used antibiotic in veterinary medicine, with both antibacterial and antiprotozoal activity, that can be used to manage various gastrointestinal (GI) diseases, anaerobic bacterial infections and giardiasis.
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Metronidazole medication was first used in humans and has been extensively used in dogs under veterinary supervision and is generally safe at the proper dosage. It is not, however, a treatment for all cases of diarrhea and recent veterinary research indicates that routine use for uncomplicated diarrhea and some chronic GI diseases may not be beneficial, and may actually upset the normal gut flora.
Since the correct dosage of Flagyl for dogs varies based on the condition, your dog's overall health, the prescribed dosage schedule, and your dog's body weight, do not administer Flagyl without your veterinarian's advice. Administering excessive amounts may lead to side effects including vomiting, loss of appetite, drooling, lethargy, or neurological issues like unsteady walking (ataxia), tremors and seizures, particularly if given in high doses or over a long period of time. Fortunately, most adverse effects resolve after the drug is stopped and proper veterinary care had been provided.
This comprehensive guide includes a Flagyl dosage for dogs calculator, recommended dosage ranges, dosage charts for various weights, tips on giving Flagyl tablets and liquid, the common uses of Flagyl, possible side effects, safety considerations, drug interactions, some of the latest research on when Flagyl is and isn't the best choice, and answers to the most frequently asked questions from a veterinarian's perspective.
No matter what type of diarrhea treatment your veterinarian recommends, or whether your dog is being treated for another condition that will necessitate the use of metronidazole, this guide will help you understand the medication and how to use it as safely and effectively as possible under your veterinarian's guidance.
Key Takeaways
- Flagyl® (metronidazole) is an antibiotic and anti-protozoal drug that is commonly prescribed to dogs for the treatment of anaerobic bacterial infections, giardiasis (a parasitic infection), gastrointestinal disease and inflammatory bowel disease (IBD) in certain cases.
- Flagyl® (metronidazole) is not FDA approved for dogs, but is commonly used off label due to its extensive history of safe use in dogs.
- The correct Flagyl dosage for dogs are based on your dog's weight, medical condition, age and overall health, and should be used as directed by a veterinarian.
- While metronidazole dosage for dogs is commonly used to treat diarrhea, it is not an effective treatment for all types of diarrhea, and the current research suggests it may not be effective for many uncomplicated cases, and may be detrimental to gut health.
- Symptoms include diarrhea, drooling, loss of appetite, vomiting, nausea, and at times dark or reddish-brown urine.
- Serious side effects, particularly at high doses or with long-term use, include loss of coordination (ataxia), shivering, weakness, abnormal eye movements, convulsions, and other neurological symptoms, all of which must be treated by a veterinarian right away.
- Extra precautions or an alternative medication may be necessary for dogs with liver disease, kidney disease, seizure disorders, low white blood cell counts, pregnant dogs or very young dogs.
- Do not change dosage, skip doses or stop early use unless directed by your veterinarian, since these will affect its effectiveness and can create complications.
- Make sure to tell your veterinarian if your dog is taking any other medications or supplements as metronidazole can interact with some.
- If symptoms do not improve or get worse, or if they don't go away after treatment or serious side effects occur, call your veterinarian right away for additional assessment.
Flagyl (Metronidazole) Dosage Chart For Dogs
Here is the standard clinical dosage and treatment duration table for metronidazole (Flagyl) in dogs, based on veterinary guidelines.
| Condition | Target Dose (mg/kg) | Target Dose (mg/lb) | Dosing Frequency | Standard Duration |
| Giardia | 10–15 mg/kg | 4.5–6.8 mg/lb | Twice daily (Every 12 hours) | 5–7 days |
| Anaerobic Bacterial Infection | 15–20 mg/kg | 6.8–9.1 mg/lb | Twice daily (Every 12 hours) | 7–10 days |
| IBD / Chronic Diarrhea | 15–25 mg/kg | 6.8–11.4 mg/lb | Twice daily (Every 12 hours) | 5–10 days (or longer under vet supervision) |
| Clostridium Perfringens | 10–15 mg/kg | 4.5–6.8 mg/lb | Twice daily (Every 12 hours) | 5–7 days |
Formulation Note: Metronidazole tablets are most commonly distributed in 250 mg and 500 mg strengths. For very small dog profiles, a custom compounded liquid formula is typically prescribed by veterinarians to avoid splitting pills into unsafe or inaccurate sizes.
What Is Flagyl (Metronidazole) for Dogs, and How Does It Work?
For veterinarians, Flagyl® (metronidazole) is a prescription antibiotic/antiprotozoal medication used to treat a number of bacterial and protozoal infections in dogs. Metronidazole belongs to the nitroimidazole group of antibiotics and is most commonly used to treat Giardia (Giardia duodenalis) infection, diarrhea and other gastrointestinal (GI) conditions caused by susceptible organisms. It is able to cross the central nervous system (CNS), bones and body tissues, and may be used to treat a few types of infections of the brain, spinal cord or bone when indicated.
Dog antibiotic dosage acts by crossing into cells of anaerobic bacteria (bacteria that grow in areas with low oxygen) and disrupting the DNA, which results in the loss of normal DNA structure, separation and non-function. This will halt the growth and multiplication of the bacteria and cause them to die. It is not fully understood how it works against protozoal parasites but it is thought to also act as a parasite killer by interfering with the DNA of protozoal parasites.
The only FDA approved metronidazole product for dogs is the oral liquid (Ayradia®), which is specifically labeled for Giardia duodenalis infections in dogs and puppies. Any other veterinary uses of metronidazole such as tablets, capsules, injectable form and for other indications are extrapolations and are classified as extra-label (off-label). This indicates that they are not approved by the FDA for these purposes; rather they are legally prescribed by veterinarians and evidence exists that they are safe and effective for these uses.
Metronidazole tablets, capsules, injectable and oral liquid are prescription-only medications and compounded versions of Metronidazole can be used if a pet requires a specific dose, or if the flavor is an issue. Regular tablets can be very bitter, making administration a challenge. Once a dose is administered, the medication starts to be effective in 1-2 hours, but expect to see improvement in your dog's symptoms in several days, depending on the condition being treated.
What Is Metronidazole Used for in Dogs?
Metronidazole (Flagyl®) is a antibiotic and anti-protozoal drug that veterinarians may use to treat a number of bacterial, protozoal and gastrointestinal (GI) diseases in dogs. It is usually prescribed to treat diarrhea caused by the susceptible bacteria or parasites, especially when the changes in the diet don't help.
Metronidazole medication for dogs is used extensively in veterinary medicine, but most of its applications in dogs are extra-label (off-label) applications, which is to say that they are used in dogs as a result of evidence that they are safe and effective, rather than because they are FDA approved for use in dogs. Ayradia® oral liquid is the only FDA-approved veterinary metronidazole product; it is indicated for the treatment of Giardia duodenalis infection in dogs and puppies.
Common Doggy Indications of Metronidazole
Metronidazole is recommended for the following conditions:
- Giardia (Giardia duodenalis) infections
- Anaerobic bacterial infections
- Acute or sudden onset of diarrhea from sensitive bacteria or parasites
- Gastrointestinal (GI) infections (acute and chronic)
- Serving as a case of inflammatory bowel disease (IBD)
- Intestinal infections
- Abscesses such as abdominal abscesses.
- Amebiasis
- Trichomoniasis
- Infections of the ears that develop from bacteria that are susceptible to treatment.
- Gum disease (periodontal infections)
- Some bone or joint infections (some types of arthritis)
- Dogs with portosystemic (liver) shunts should be supported with treatment.
How Metronidazole Is Given
There are a number of formulations of metronidazole:
- Tablets
- Capsules
- Oral liquid
- Capsules, powder, injection (for veterinary hospitals)
Can be given with or without food, but may be given with a small meal to minimize upset. Liquid formulations should be thoroughly shaken prior to use. Never give your dog more or less of any medication or supplement, always follow your veterinarian's directions and inform him/her of any other medication or supplement your dog is taking including any herbal products. Never discontinue treatment without your veterinarian's direction.
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Current Research Says:
Metronidazole dose is still a valuable drug for certain infections but new research in veterinary medicine has altered its use for diarrhoea.
Studies suggest that:
- Not the best treatment for most cases of acute, non-specific diarrhea.
- Probiotics, synbiotics and dietary management can give comparable and/or better effect without disturbing the normal gut flora.
- Metronidazole is not consistently effective in the treatment of an overgrowth of E coli in the intestine.
- Some protozoal infections are now becoming resistant to metronidazole treatment.
- Metronidazole drug for dogs is not effective for inflammatory bowel disease (IBD) when combined with prednisone over prednisone alone.
- In light of these findings, it is now recommended that metronidazole should only be used when there is a clear indication for it rather than routinely as a treatment for all dogs with diarrhea.
What Are the Benefits of Metronidazole?
When used under the guidance of a veterinarian, metronidazole (Flagyl®) has a number of advantages for dogs. It is an antibiotic and antiprotozoal drug that is useful for some anaerobic bacterial infections, and against protozoal parasites. Among its main benefits is its capacity to cross the blood–brain barrier and enter the bone tissues as well as the spinal cord, where it is able to treat infections in locations where numerous antibiotics are inadequate.
Metronidazole is beneficial to dogs in several ways
- Effectively treats anaerobic bacterial infections.
- Assists with the control of diarrhea due to susceptible bacterial or protozoal infections.
- In appropriate cases reduces inflammation of the intestinal tract.
- Usually used in dogs to treat Giardia (Giardia duodenalis) infections.
- Knows how to penetrate the central nervous system (brain and spinal cord), so it can be used in some neurological infections.
- Capable of penetrating bone tissue making it able to treat some bone related bacterial infections.
- There are a number of different formulations available such as tablet, capsule, oral liquid and injectable that can be used for administration to suit the individual patient.
- Acts promptly following administration, but usually clinical improvement can be seen within several days.
What Are the Side Effects of Metronidazole in Dogs?
Metronidazole (Flagyl®) is generally well tolerated by most dogs when administered at the recommended dose but, as with all drugs, may have side effects. Common side effects are in the digestive system, such as diarrhea, loss of appetite, nausea, stomach upset and vomiting. Metronidazole tastes very bitter and some dogs may salivate profusely, gag, froth at the mouth or vomit, particularly if a tablet is crushed.
Medication may also decrease healthy bacteria in the gut and change the balance of bacteria leading to potential longer-term changes in the gut and to increased diarrhea. Other minor complications are tiredness, weakness, lethargy, fever, and dark/discoloured urine. Usually these side effects are not serious and will get better in a few days after the medicine is discontinued.
Common Side Effects
The most common side effects reported are:
- Nausea
- Vomiting
- Diarrhea
- Stomach upset
- Loss of appetite (anorexia)
- Over Production of Saliva
- Gagging or regurgitation
- Salivating and frothing at the mouth
- Fatigue or lethargy
- Weakness
- Fever
- Dark or coloured urine.
- Disturbance of normal gut bacteria, which can lead to diarrhoea
Serious Side Effects
While rare, severe side effects call for immediate veterinary care:
- Nervous system toxicity (neurotoxicity) particularly after high doses or long-term use (over two weeks), liver disease or over dose.
- Walking difficulty (ataxia) or "drunken gait.
- Loss of balance or co-ordination
- Head tilt
- Quick, uncontrolled eye movements, or eye twitching (nystagmus)
- Muscle contractions or shaking of the body
- Muscle spasms
- Feeble or unable to stand.
- Disorientation or confusion
- Seizures or convulsions
- Yellowing of the skin, gums or eyes (jaundice)
- Uncommon skin reactions such as hair loss, bruising, swelling, or scaling
- Unusually low levels of blood cells in rare instances
Who is at a Higher Risk?
There is a higher risk for serious side effects in:
- Dogs that are given high daily doses (particularly >30 mg/kg or >13.6 mg/lb)
- Dogs that receive more than 14 days of treatment
- Dogs with liver disease or liver dysfunction.
- Frail dogs
- Because of their body weight, small dogs may be more susceptible to neurotoxicity.
- Pregnant or lactating bitches (females) – metronidazole is not generally recommended and has caused birth defects in some instances.
If any side effects do occur, a doctor needs to be contacted
If your dog develops any neurological symptoms such as vomiting, severe diarrhea, excessive salivation, wobbliness, tremors, seizures, difficulty walking, eye twitching, etc. stop the Flagyl (metronidazole) medication right away and call your vet or emergency veterinary hospital.
With supportive care, the majority of metronidazole-induced neurotoxicity is reversible upon discontinuation of the drug and may take days to weeks. Treatments, such as diazepam (Valium®), will in many cases help to speed up recovery. If an overdose or severe reaction is suspected, get veterinary help as soon as possible.
Are There Any Interactions Between Metronidazole and Other Medications?
Yes. Metronidazole (Flagyl® Dosage For Dogs) may interact with a number of other medications, which can cause more side effects or make it less effective. Tell your veterinarian if your dog is taking any other prescription, over-the-counter (OTC), vitamins, minerals, herbals, or dietary supplements prior to beginning metronidazole. This will help your veterinarian prevent potential drug interactions and decide if a medication needs to be adjusted, if more monitoring is required, or if a different medication is necessary.
Drugs that should not be combined with Metronidazole
- Warfarin (Coumadin®): Metronidazole for dogs may enhance the effect of this blood-thinning medication, which may lead to bleeding. Your vet may decrease the warfarin dose, if necessary, and monitor your dog more closely.
- Cimetidine: This medication may interfere with the breakdown of metronidazole and cause it to build up in the body and cause side effects.
- Phenobarbital: This seizure medication can cause metronidazole to be eliminated more quickly, making the antibiotic less effective.
- Phenytoin (Dilantin®): As with phenobarbital, phenytoin can decrease the effectiveness of metronidazole by speeding up the way it is broken down in the body.
- Cyclosporine (Atopica®): Cyclosporine levels may be raised by metronidazole which may lead to cyclosporine-related side effects. Further monitoring or dose adjustments may be needed.
- Fluorouracil (5-FU): Metronidazole may be used with fluorouracil, but may enhance the blood levels of 5-FU to possibly toxic levels.
Important Safety Tips
- Be sure to tell your vet the names of all of the products your dog receives, including prescription drugs, OTC products, vitamins, supplements and herbs.
- Avoid changing or stopping any medication without veterinarian's instruction while your dog is on metronidazole.
- These are not the only medications which can interact with each other. Your veterinarian will be able to advise you on whether or not metronidazole can be used along with your other treatment and the proper monitoring that should be done if necessary.
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FAQs
For what is Flagyl (metronidazole) used for dogs?
Flagyl (metronidazole) Dosage For Dogs is a antibiotic and antiprotozoal drug that is used to treat anaerobic bacterial infections, Giardia infections and some gastrointestinal conditions and diarrhea caused by susceptible bacteria or parasites. It can also be prescribed for other infections when appropriate by your veterinarian.
How long will metronidazole take to work for a dog?
Metronidazole drugs for dogs starts to work in about 1-2 hours after taking it. Most dogs, however, don't notice much of a difference until several days after that, depending on the condition that is being treated and the severity of the infection.
Is it okay to give my dog metronidazole without a vet's prescription?
No, Metronidazole is a prescription drug and should only be administered under veterinary supervision. Treatment failures or adverse reactions may occur if the wrong dose is used, or if it is used for the wrong condition.
If you miss a dose of metronidazole, what should you do?
In the event of a missed dose, it should be administered as soon as possible unless the next dose is due in less than an hour. If you do, do not make up the missed dose, but resume the usual schedule. Do not double dose to compensate for a missed dose.
May metronidazole be given with food?
Yes. Metronidazole dose can be given with or without food. If your dog becomes upset in the tummy when taking it on empty tummy, try offering it with a little food or treat to help minimise tummy upset.
Does metronidazole interact with other drugs?
Yes. Certain drugs may interact with metronidazole, including warfarin, cimetidine, phenobarbital, phenytoin, cyclosporine and fluorouracil (5-FU). Before beginning treatment, always be sure to inform your veterinarian about any other medications, vitamins, supplements or herbal products that your dog is taking.
Final Thoughts
Metronidazole (Flagyl®) Medication for dogs is a very useful antibiotic and anti-protozoal drug that can be used to treat Giardia infection, anaerobic bacterial infections, and some gastrointestinal diseases in dogs, but only under veterinary supervision. It is not, however, the appropriate treatment for all cases of diarrhoea and many dogs with mild or uncomplicated diarrhoea will be fine with appropriate dietary management and/or probiotics or other treatments. Your veterinarian will decide if metronidazole is right for your dog, depending on your dog's symptoms, diagnosis and health status.
To achieve best results, metronidazole should always be administered as directed by your veterinarian, and the prescribed course of treatment should be completed, unless your veterinarian advises otherwise. This will help clear the infection, decrease the chances of it returning, and help with successful treatment. Most dogs do fine on short-term therapy, but watch your dog for side effects like vomiting, diarrhea, loss of appetite, drooling, wobbliness, tremors, or odd behavior. If any signs of neurologic activity are noticed, cease the use of the medication immediately and call the veterinarian right away.
If your dog does not improve in a few days or if the diarrhea gets worse on the medications, or if it gets worse after the meds are done, do not continue to give it on your own, get it examined again. Your vet may also suggest changing your dog's diet after therapy or supplementing with probiotics to help restore the balance of gut bacteria and promote digestive health. Metronidazole can be a safe and effective treatment for your dog, with the right diagnosis, dosage and with your vet's guidance.
