Metronidazole for Dogs (Uses, Side Effects & Dosage)

Is your dog suffering from severe diarrhea, oral pain, or parasites? Your vet may suggest using a human medication called metronidazole. Though this medication is made for human use, it’s generally considered safe and effective by veterinarians nationwide.

As with any medication, there are a few things to know when starting your dog on metronidazole, including what to expect, any severe side effects to look out for, and possible drug interactions that may be dangerous for your dog.

Interested in learning more about metronidazole? Read on to learn all about this medication and how to safely administer it to your dog. Or, use the links below to jump ahead to a section of your choosing.

• What is Metronidazole?
• What is Metronidazole Used for?
• Metronidazole Administration and Dosage
• Side Effects of Metronidazole in Dogs
• Metronidazole Risks and Drug Interactions
• FAQS
• Final Notes

What is Metronidazole?

Metronidazole, commonly known by brand names Flagyl, Metizol, Prostat, and more, is an antibiotic widely used to treat large intestine infections and inflammation in dogs. Though it’s a medication created for humans, veterinary science has discovered it’s effective in treating animals, too. Though the FDA hasn't approved it, many veterinarians find its off-label use in dogs safe.

Metronidazole can be useful in treating various bacterial and parasitic infections in dogs. These include conditions like¹:

• Parasites like Giardia and Coccidiosis
• Inflammatory bowel disease
• Oral and dental infections

Metronidazole Facts

• Common names: Flagyl, Metizol, Prostat, Metrogel
• Typical uses: Severe diarrhea, IBD, Giardia, Trichomoniasis, amebic dysentery, bacterial infections
• Standard dosage: 10-25 mg/kg of weight
• Common side effects: Diarrhea, nausea, lack of appetite, fatigue, discolored urine
• Less common side effects: neurologic disorders, lethargy, weakness, hepatotoxicity and hematuria

How it Works

Metronidazole is both an antibiotic and antiprotozoal. Let’s explore what these terms mean:

• Antibiotic: Antibiotic drugs address “bad” bacteria that live in your dog and make them sick. Antibiotics may kill or prevent bacteria from multiplying, therefore stopping the infection.²
• Antiprotozoal: Antiprotozoals treat infections caused by single-cell parasites known as protozoa. These include common infections like Giardia and Coccidiosis. These medications either kill the parasites or prevent them from reproducing.

Research also suggests that metronidazole can lower inflammation by suppressing the immune system, making it a potentially effective treatment for inflammatory bowel disease.³

What is Metronidazole Used for?

Metronidazole can be used to treat a host of bacterial and parasitic infections in dogs, including³:

• Abscesses: Puss-filled lumps often caused by bacterial infections
• Amebic dysentery: A parasitic intestinal disease spread by human feces
• Anaerobic bacterial infections: Infections caused by bacteria that thrive in oxygen-free environments like the gums and wounds
• Inflammatory bowel disease: Inflammation of the GI tract that disrupts digestion
• Giardia: A common parasite that can cause diarrhea, vomiting, weight loss, and other GI issues
• Trichomoniasis: An oral infection caused by parasites in the intestinal tract.

Metronidazole is also commonly used to treat severe diarrhea in dogs and may be prescribed even when the cause of diarrhea can't be determined.

Metronidazole Administration and Dosage

If you think your dog may benefit from Metronidazole, it’s time to talk to your vet. They can help determine whether the medication may help your dog’s health and how it should be administered. Metronidazole or metronidazole benzoate is available in oral liquids, pills, topical ointments, and injections.

Your vet will also determine a dosage that’s best for your dog’s needs. The dosage will depend on your dog's breed, size, and the type of infection or illness being treated. In general, the dose ranges from 5-20 mg/kg of body weight, but dosage can vary.⁴ For instance:

• Dogs suffering from giardiasis typically get a dosage of 25 mg/kg every 12 hours for five days
• Dogs with inflammatory GI issues or IBD may receive 10-15 mg/kg every 12 hours

Depending on your dog’s condition, metronidazole or metronidazole benzoate may be prescribed in tandem with other medications. It’s important to follow your vet’s instructions to ensure your dog is being treated properly.

Metronidazole can be bitter, so you may need to find ways to entice your dog to swallow their medication. In most cases, masking the pill in a piece of cheese should help, but if you have issues administering the drug to your pet, call your vet for advice.

The medication takes effect within a few hours, and you should notice gradual improvements after a few days.

Side Effects of Metronidazole in Dogs

Metronidazole for dogs is considered relatively safe and adverse side effects are uncommon. However, pet owners may notice that their dog's urine is reddish-brown due to pigments in the medication. Additional common side effects include³:

• Diarrhea
• Nausea
• Excessive drooling
• Lack of appetite
• Lethargy

In rare cases, dogs taking metronidazole can experience signs of neurotoxicity, with symptoms such as³:

• Tremors
• Muscle spasms
• Ataxia
• Convulsions
• Paralysis

Other rare side effects of metronidazole include³:

• Liver damage: If you notice yellowing of the eyes, gums, or skin, contact your vet immediately
• Cutaneous vasculitis: This condition causes blood vessels to become inflamed and skin to swell and bruise

As with any medication, you should monitor your dog for signs of allergic reactions. This includes³:

• Hives and rash
• Rapid heartbeat
• Difficulty breathing

If you suspect your dog is having an allergic reaction to metronidazole, contact your vet immediately.

Because metronidazole is a short-acting medication, any minor symptoms should subside within a day after they stop taking the drug. Additionally, most minor side effects should improve over the course of your dog's treatment. However, if you're worried about your dog's side effects, contact your vet to let them know and determine whether your dog should stop or continue treatment.

Metronidazole Risks and Drug Interactions

Although metronidazole and metronidazole benzoate are considered to be relatively safe medications for dogs, there are some health risks and drug interactions to be aware of.

Risks

In some cases, metronidazole may be harmful to your dog’s health. In general, dogs that should not take metronidazole include:

• Pregnant and nursing females
• Dogs with an allergy to the medication or related drugs
• Dogs with weakened immune systems
• Puppies under 8 weeks old

Drug Interactions

Some drugs may interact with metronidazole, including supplements, flea medications, chemotherapy drugs, and more. Potential interactions include³:

• Cimetidine
• Cyclosporine
• Phenobarbital
• Phenytoin
• Warfarin

If your dog is taking other drugs, tell your vet to ensure they won't experience any adverse reactions that may cause one medication to become ineffective or even harmful to your dog's health.

Overdose

It is possible for your dog to overdose on metronidazole, though it should be avoidable as long as you follow your vet’s instructions. A typical overdose of metronidazole is greater than 30 mg/kg/day.⁵ Overdoses are a medical emergency, so if you notice any of these symptoms, take your dog to the nearest emergency vet clinic as soon as possible:

• Vomiting
• Difficulty walking
• Disorientation
• Extreme fatigue
• Stiffness
• Seizures

If your dog takes more metronidazole than they're supposed to, they'll require immediate treatment to limit medication absorption and potentially harmful symptoms.

FAQS

How fast does metronidazole work in dogs?

The medication in metronidazole begins working just a few hours after your dog consumes it. Once they digest the pill, the medication will combat harmful bacteria and protozoa that may be causing your dog’s illness. That said, you should notice the results of metronidazole within a few hours after ingesting the medication. Progression may be slow and steady but should improve over time.

What bacteria does metronidazole get rid of?

Metronidazole addresses anaerobic bacteria, which thrive in environments with less oxygen. In dogs, low-oxygen environments include the gums and any damaged tissue, such as wounds, abscesses, and other injuries.¹ Metronidazole is able to address these types of bacteria directly, making it an extremely effective medication for treating oral infections and infections in wounds and sores.

How should metronidazole be stored?

Metronidazole for dogs should be stored at room temperature; typically, anything between 59 to 77 degrees Fahrenheit is okay. It's best to keep it in a dark, dry area where you store the rest of your medications and supplements.⁴

Additionally, you should always keep medication out of reach of children and pets. Even though overdoses are rare because this medication is bitter, it's not worth the risk. Therefore, keep your medication in a cabinet or closet where your children and pets can't reach them.

Is metronidazole an antibiotic for dogs?

Yes, metronidazole, also known as Flagyl for dogs, is a popular antibiotic used by vets to treat diarrhea and inflammation issues in the digestive tract. It can even be used to treat gum disease since it targets bacteria.

Final Notes

Metronidazole is an effective treatment for many infections caused by bacteria and protozoan parasites, especially infections in the digestive tract. Most side effects are minor, though there can be severe symptoms.

Worried about your dog's health? Talk to a Dutch vet. We can help you fix your dog's nutrition, learn about why dogs have diarrhea, diagnose the underlying cause of your dog's GI issues, and help you treat them, with or without medication. Plus, all Dutch members get free shipping on online pet pharmacy orders. Join Dutch today.