Medically Review By: Medsdog Team
Last Updated: August 2026
Metronidazole is an antiprotozoal medication and an antibiotic that finds extensive use in veterinary medicine. It works by interfering with the DNA of anaerobic bacteria and protozoa so that they stop growing.
Metronidazole is popularly used to treat dogs with diarrhea, gastrointestinal infections, and some of the bacterial and protozoal infections.
Correct dosage varies according to the weight of my dog, the condition under treatment and the length of time of treatment, usually in mg/kg or mg per kilogram.
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Beside other useful information there is the Metronidazole dosage for dog’s calculator and chart included in this guide which helps a pet owner to know the safe dose of Metronidazole.
Disclaimer: All the information in this guide is for informational purposes only and will never replace your vet advice.
Flagyl (Metronidazole) Dosage Calculator for Dogs
Estimate a starting dose based on your dog’s weight and the product you have on hand.
| Body Weight | 0 lb (0 kg) |
| Dose Rate Used | 25 mg/kg (11.3 mg/lb) |
| Typical Frequency | Every 12 hours (per vet direction) |
Metronidazole Dosage for Dogs Overview
- Popular Brand names Flagyl, Metizol, Protostat, Metrogel
- The standard metronidazole dosage for dogs is 10 to 50 mg/kg (about 5 to 30 mg/lb) one to 4 times a day, depending on the condition being treated.
- Giardia infections are treated at the high end of the range up to 25 mg/kg.
- Metronidazole is not FDA-approved for dogs in the U.S. (except one specific liquid formulation for Giardia), so all dosing is done off-label under veterinary supervision.
- Doses above roughly 60 mg/kg, or prolonged courses beyond 2 weeks, carry a meaningfully higher risk of neurological side effects.
What is Metronidazole for Dogs
Metronidazole is an antiprotozoal medication and an antibiotic that finds extensive use in veterinary medicine. It works by interfering with the DNA of anaerobic bacteria and protozoa so that they stop growing.
It is frequently prescribed by veterinarians as:
- Acute or chronic diarrhea
- Giardia infections
- IBD Inflammatory bowel disease (IBD)
- Dental or oral infections
- Some gastrointestinal disorders of the liver.
What is the Safe Metronidazole Dosage for Dogs?
The recommended metronidazole dosage for the treatment of infections caused by Giardia, Trichomonas, and Balantidium coli is 10 to 50 mg/kg (about 5 to 30 mg/lb) one to four times a day, depending on the condition being treated.
Remember, this dose can be increased or decreased by your vet after examining certain conditions, including breed, weight, health condition, response to the medicine, and medications your furry friend is already taking.
Flagyl Metronidazole Available Strength
- 250 milligram tablets
- 500 milligram tables
- 375 milligram capsules
- 200 mg of metronidazole per 5 ml of liquid
Metronidazole Dosage Chart for Dogs by Weight
| Dog Weight | Weight (kg) | 10 mg/kg Dose | 20 mg/kg Dose | 30 mg/kg Dose | 40 mg/kg Dose | 50 mg/kg Dose |
|---|---|---|---|---|---|---|
| 5 lb | 2.3 kg | 23 mg | 45 mg | 68 mg | 91 mg | 113 mg |
| 10 lb | 4.5 kg | 45 mg | 91 mg | 136 mg | 182 mg | 227 mg |
| 15 lb | 6.8 kg | 68 mg | 136 mg | 204 mg | 272 mg | 340 mg |
| 20 lb | 9.1 kg | 91 mg | 182 mg | 273 mg | 364 mg | 455 mg |
| 25 lb | 11.3 kg | 113 mg | 227 mg | 340 mg | 454 mg | 567 mg |
| 30 lb | 13.6 kg | 136 mg | 272 mg | 408 mg | 544 mg | 680 mg |
| 40 lb | 18.1 kg | 181 mg | 363 mg | 544 mg | 726 mg | 907 mg |
| 50 lb | 22.7 kg | 227 mg | 454 mg | 681 mg | 908 mg | 1,135 mg |
| 60 lb | 27.2 kg | 272 mg | 544 mg | 816 mg | 1,088 mg | 1,360 mg |
| 70 lb | 31.8 kg | 318 mg | 636 mg | 954 mg | 1,272 mg | 1,590 mg |
| 80 lb | 36.3 kg | 363 mg | 726 mg | 1,089 mg | 1,452 mg | 1,815 mg |
| 90 lb | 40.8 kg | 408 mg | 816 mg | 1,224 mg | 1,632 mg | 2,040 mg |
| 100 lb | 45.4 kg | 454 mg | 908 mg | 1,362 mg | 1,816 mg | 2,270 mg |
Flagyl® 250mg, 500mg Tablets Dosage Chart for Dogs
| Dog Weight | Weight (kg) | Approx. Dose at 25 mg/kg | 250 mg Tablet | 500 mg Tablet |
|---|---|---|---|---|
| 5 lb | 2.3 kg | 58 mg | ¼ tablet | — |
| 10 lb | 4.5 kg | 113 mg | ½ tablet | ¼ tablet |
| 15 lb | 6.8 kg | 170 mg | ¾ tablet | ¼ tablet |
| 20 lb | 9.1 kg | 227 mg | 1 tablet | ½ tablet |
| 25 lb | 11.3 kg | 283 mg | 1¼ tablets | ½ tablet |
| 30 lb | 13.6 kg | 340 mg | 1½ tablets | ¾ tablet |
| 40 lb | 18.1 kg | 454 mg | 2 tablets | 1 tablet |
| 50 lb | 22.7 kg | 567 mg | 2¼ tablets | 1¼ tablets |
| 60 lb | 27.2 kg | 680 mg | 2¾ tablets | 1½ tablets |
| 70 lb | 31.8 kg | 795 mg | 3¼ tablets | 1½ tablets |
| 80 lb | 36.3 kg | 908 mg | 3¾ tablets | 1¾ tablets |
| 90 lb | 40.8 kg | 1,020 mg | 4 tablets | 2 tablets |
| 100 lb | 45.4 kg | 1,135 mg | 4½ tablets | 2¼ tablets |
Important: The fractions above are mathematical approximations to the 25 mg/kg dose, not a substitute for a veterinarian's prescription. Human Flagyl tablets are prescription products, and not every human tablet is scored or designed to be split into quarters.
Flagyl® 200 mg/5ml Liquid Suspension Dosage Chart for Dogs
| Dog Weight | Weight (kg) | Calculated Dose | Flagyl 200 mg/5 mL Volume |
|---|---|---|---|
| 5 lb | 2.3 kg | 57.5 mg | 1.4 mL |
| 10 lb | 4.5 kg | 112.5 mg | 2.8 mL |
| 15 lb | 6.8 kg | 170 mg | 4.3 mL |
| 20 lb | 9.1 kg | 227.5 mg | 5.7 mL |
| 25 lb | 11.3 kg | 282.5 mg | 7.1 mL |
| 30 lb | 13.6 kg | 340 mg | 8.5 mL |
| 40 lb | 18.1 kg | 452.5 mg | 11.3 mL |
| 50 lb | 22.7 kg | 567.5 mg | 14.2 mL |
| 60 lb | 27.2 kg | 680 mg | 17.0 mL |
| 70 lb | 31.8 kg | 795 mg | 19.9 mL |
| 80 lb | 36.3 kg | 907.5 mg | 22.7 mL |
| 90 lb | 40.8 kg | 1,020 mg | 25.5 mL |
| 100 lb | 45.4 kg | 1,135 mg | 28.4 mL |
Recommended dose used for this chart: 25 mg/kg (11.3 mg/lb) per dose every 12 hours. Veterinary references identify this regimen for canine giardiasis; other conditions can require different metronidazole doses and frequencies.
Metronidazole Dosage by Condition (mg/kg Per Day)
| Condition | Typical Dose | Frequency | Typical Duration |
|---|---|---|---|
| Acute diarrhea / general GI upset | 10 mg/kg/day | Every 12 hrs | 3–5 days |
| Inflammatory bowel disease (IBD) | 10–15 mg/kg/day | Every 12 hrs | Vet-directed, often 10–14 days |
| Giardia | 25 mg/kg/day | Every 12 hrs | 5–7 days |
| Hepatic encephalopathy | 7.5 mg/kg/day | Every 8–12 hrs | Vet-directed (often long-term, at reduced rate) |
Metronidazole Dosage for Puppies
Puppies can be prescribed metronidazole, most commonly for Giardia picked up at a shelter, breeder, or dog park, but dosing needs extra caution:
- Puppies under about 12 weeks old are generally not given metronidazole unless a vet has specifically weighed the risks and benefits.
- Because puppies gain weight quickly, a dose calculated even a few weeks ago may already be outdated always re-weigh before refilling a prescription.
- Puppies are more sensitive to dehydration from GI illness, so hydration and nutrition support alongside the medication matter more than in adult dogs.
Never use an adult dosing chart to estimate a puppy's dose without vet confirmation get a same-day weight and a fresh calculation instead.
How Long Does Metronidazole Take to Work in Dogs?
Metronidazole is absorbed quickly usually within 1–2 hours but symptom improvement in canines takes longer. Most owners see firmer stools within 24–48 hours for simple diarrhea, while Giardia cases typically need the full 5–7 day course before the parasite is cleared.
Even if your furry friend seems back to normal early, finish the entire prescribed course unless your vet tells you otherwise; stopping early is one of the more common reasons infections return.
Side Effects & Safety Warnings
Common Side Effects
- Nausea or vomiting
- Loss of appetite
- Drooling
Serious (Seek Vet Care Immediately)
- Tremors or seizures
- Loss of coordination (ataxia)
- Head tilt or eye twitching
Metronidazole Drug Interactions in Dogs
| Interacting Drug | What Happens |
|---|---|
| Warfarin / other anticoagulants | Increased bleeding risk |
| Cimetidine | Stronger metronidazole effect, higher side-effect risk |
| Phenobarbital, phenytoin | Can reduce metronidazole's effectiveness |
| Cyclosporine (Atopica) | Increased risk of cyclosporine-related side effects |
Which Dogs Should Not Take Metronidazole
Metronidazole isn't right for every pooch. Your vet will likely avoid it, or use a much lower and closely monitored dose, in canines that are:
- Pregnant (linked to birth defects in lab studies) or nursing (passes into milk)
- Living with liver disease or reduced liver function
- Prone to seizures or on seizure medication
- Known to have a hypersensitivity or prior allergic reaction to metronidazole
- Very young puppies (see Puppies section)
Suspected Overdose: What to Do
If your furry friend ingests more than the recommended dosage, whether from a dosing mistake or getting into a pill bottle act immediately rather than waiting for symptoms:
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- Call your veterinarian or the nearest emergency animal hospital right away.
- If it's after hours, contact a poison control hotline:
- ASPCA Animal Poison Control Center: (888) 426-4435
- Pet Poison Helpline: (855) 764-7661 (a consultation fee may apply)
- Have the medication packaging on hand, and note the estimated amount and time ingested.
- Do not induce vomiting unless a veterinary professional specifically instructs you to.
A Safety Note: Ivermectin for Dogs Without a Vet
Because metronidazole and ivermectin are sometimes searched together as general "deworming" or GI medications, it's worth a clear warning: never dose ivermectin without veterinary guidance. Collies, Shelties, Australian Shepherds, and related breeds can carry the MDR1 gene mutation, which makes even small doses of ivermectin potentially fatal. If you're researching parasite treatments, see our full ivermectin safety guide before giving anything at home.
Are There Alternatives to Metronidazole for Dogs?
Depending on what's actually causing your pup's symptoms, your vet may reach for a different medication entirely:
- Giardia specifically: fenbendazole is a common alternative or add-on see our fenbendazole for treating dog giardia or the related Panacur fenbendazole brand.
- Severe antibiotic-responsive diarrhea: vets sometimes combine metronidazole with another antibiotic for a faster effect commonly paired with our enrofloxacin in more resistant cases.
- General bacterial GI infections: amoxicillin/clavulanate is another first-line option see our Clavamox (amoxicillin/clavulanate) guide.
- Supportive rehydration during any GI illness: an oral electrolyte solution can help alongside prescribed medication see our Pedialyte electrolyte for canines.
- Dietary management, probiotics, and added fiber are also commonly used either instead of or alongside medication for milder cases.
How Metronidazole Calculator for Dogs works
How the math works: the calculator multiplies your dog's weight in kilograms by the prescribed mg/kg rate. If you only know your dog's weight in pounds, it's converted to kilograms first (1 kg ≈ 2.2 lb) before the mg/kg rate is applied this keeps the pound-based and kilogram-based results consistent with each other and with the published veterinary literature.
FAQs
Can I give metronidazole to my dog without a vet?
No. Although dosage calculators are helpful, prescription oversight is critical.
Puppies, such as pinpointing in metronidazole, it is safe?
Sometimes-but dosing needs to be carefully adjusted by a veterinarian.
Is metronidazole allowed to be mixed with food?
Yes, and it often does relieve the upset stomach.
What if I miss a dose?
Give it when remembered except if close to the next dose - never double dose.
Are there alternatives to metronidazole?
Yes, based on the cause (dietary management, probiotics, dewormers).
Final Thoughts
A metronidazole dosage calculator and chart are useful tools for understanding what your vet has prescribed and catching an obvious math error before you give a dose but they're not a substitute for the diagnosis and monitoring only a veterinarian can provide.
Used correctly, at the right mg/kg rate for the right condition, metronidazole remains one of the most reliable antibiotics in veterinary GI medicine.
