Dog Metronidazole Dosage Calculator
Indication-specific metronidazole (Flagyl) dosing for dogs — covering Giardia, anaerobic infections, and inflammatory bowel disease, with tablet and suspension breakdowns.
🐶 Introduction
Metronidazole (Flagyl®) is a nitroimidazole antimicrobial agent with both antibacterial and antiprotozoal activity. It is one of the most commonly prescribed drugs in small animal practice, valued for its efficacy against anaerobic bacteria, Giardia species, Clostridium perfringens, and Helicobacter. At lower doses, it also exerts immunomodulatory and anti-inflammatory effects useful in managing inflammatory bowel disease (IBD).
Metronidazole works by entering susceptible organisms and undergoing intracellular reduction to reactive intermediates that damage DNA, disrupting nucleic acid synthesis and causing cell death. This mechanism is selective for anaerobes and protozoa because they possess the low-redox-potential ferredoxin systems required for drug activation.
📚 Indication-Specific Dosing
Giardiasis
25–50 mg/kg/day PO, divided q12h, for 5–7 days. Higher end of range for confirmed Giardia. Often combined with fenbendazole (50 mg/kg/day × 5 days) for improved efficacy.
Anaerobic Bacterial Infections
15–30 mg/kg/day PO, divided q8–12h, for 5–10 days. Covers Clostridium, Bacteroides, Fusobacterium. Often combined with a fluoroquinolone for broad-spectrum coverage.
Inflammatory Bowel Disease (IBD) — Anti-inflammatory
10–15 mg/kg/day PO, divided q12h, for 4–6 weeks. Lower dose leverages immunomodulatory effects. Used as adjunctive therapy alongside diet change.
Hepatic Encephalopathy
7.5 mg/kg PO q8h. Reduces ammonia-producing gut bacteria.
Available Formulations
- 250 mg tablets, 500 mg tablets (human pharmacy)
- 50 mg/mL oral suspension (compounded veterinary)
- Injectable: 5 mg/mL IV (hospital use)
Neurotoxicity Warning
Prolonged use (>7 days) or high doses (>60 mg/kg/day) risk metronidazole-associated neurotoxicity: ataxia, nystagmus, seizures, head tilt. These are dose-dependent and generally reversible upon discontinuation.
📋 How to Use
- Enter your dog’s weight in kg or lb.
- Select the indication — this determines the dose range.
- Choose your available formulation (250 mg tablet, 500 mg tablet, or 50 mg/mL liquid).
- Click Calculate to see daily dose, per-dose amount, and quantity of tablets or liquid.
- Always complete the full course; stopping early risks resistance.
🦠 Metronidazole Dose Calculator
Duration limit: Do not exceed 7 days without veterinary guidance. Signs of neurotoxicity (wobbling, rapid eye movements, head tilt, seizures) require immediate discontinuation and veterinary assessment. Give with food to reduce GI upset.
📖 References & Methodology
- Plumb DC. Plumb’s Veterinary Drug Handbook, 9th ed. Wiley-Blackwell, 2018. Metronidazole entry.
- Papich MG. Saunders Handbook of Veterinary Drugs, 4th ed. Elsevier, 2016.
- Scorza AV, Lappin MR. Metronidazole for the treatment of feline giardiasis. J Feline Med Surg. 2004;6(3):157-160.
- Trepanier LA. Idiosyncratic toxicity associated with potentiated sulfonamides in the dog. J Vet Pharmacol Ther. 2004;27(3):129-138.