Vet Guide 2025: Zonisamide (Zonegran) for Seizure Control in Pets 🐾🧠

By Dr Duncan Houston, BVSc 🩺

Seizures in pets can be a distressing and sometimes challenging condition to manage. While many cases are effectively controlled with medications like phenobarbital, some pets require alternative options—either due to side effects or lack of effectiveness. One such alternative is Zonisamide, a newer anticonvulsant that is gaining traction in veterinary medicine 🐶🐱💊.

🧬 What Is Zonisamide?

Zonisamide, sold under the brand name Zonegran®, is an anticonvulsant drug used to treat seizures in both cats and dogs. It is part of a class of drugs known as sulfonamides, and although originally developed for humans, it has shown promising results in pets—especially in cases where first-line seizure medications fall short 🧠🛡️.

Zonisamide is available in the following oral capsule strengths:

• 25 mg
• 50 mg
• 100 mg

💊 How Zonisamide Is Used

For Dogs 🐕

Dogs are typically dosed twice daily. Zonisamide may be used on its own or more commonly as an add-on therapy with phenobarbital in dogs experiencing breakthrough seizures. In these cases, it can help improve control without requiring extremely high doses of phenobarbital ⚖️.

For Cats 🐈

Cats, due to slower drug clearance, may be dosed once daily. Zonisamide is still relatively new in feline patients, so vets monitor closely for unexpected side effects 🧪.

🧪 Monitoring & Adjustments

Blood tests are essential to ensure safe and effective use:

• 📊 Blood levels checked 1–2 weeks after starting or adjusting dosage
• 📉 Monitoring for sedation, vomiting, appetite loss, or liver enzyme changes
• 🧪 Combination therapy (e.g., with phenobarbital) requires peak and trough level testing

Zonisamide blood levels help vets determine if the drug is within a therapeutic range, especially when seizures recur despite regular dosing ⏱️.

⚠️ Potential Side Effects

• 😴 Common: Sedation, lethargy, and drowsiness (especially early in therapy)
• 🤢 Gastrointestinal: Vomiting, appetite loss, diarrhea
• 🧪 Liver: Rare but documented cases of liver damage
• 🧂 Renal: Renal tubular acidosis and electrolyte imbalances (especially with diuretics)
• 🧠 Tolerance: Increasing doses may be needed over time for the same effect

🚨 Serious Symptoms to Report Immediately:

• 😵 Listlessness or collapse
• 🍽️ Complete refusal to eat
• 💛 Yellowing of the eyes (jaundice)

Zonisamide can also lower thyroid hormone levels, so pets on long-term therapy may need thyroid testing as part of routine care 🔍.

🤰 Safety & Handling Precautions

⚠️ Do not use in pregnant animals. Zonisamide has been linked to birth defects, especially cardiovascular abnormalities. Women of childbearing age should wear gloves when handling this medication and wash hands thoroughly afterward 🧤🧼.

🔄 Drug Interactions

Zonisamide is metabolized by the liver and interacts with several drugs:

• 💊 Phenobarbital: Accelerates zonisamide metabolism—dose adjustment likely required
• 🧴 Carbonic anhydrase inhibitors (e.g., acetazolamide, dorzolamide): Increase risk of kidney stones

Let your vet know about any other medications, including supplements, that your pet may be taking 📋.

📉 Contraindications & Cautions

• 🚫 Do NOT stop Zonisamide abruptly—can cause dangerous rebound seizures
• 🧪 Not recommended without periodic bloodwork (kidney, liver, and electrolytes)
• ⚠️ Avoid in pets with known sulfa allergies

It can be given with or without food, and most pets tolerate capsules well when hidden in a treat or pill pocket 🍖💊.

📊 Zonisamide vs. Other Anticonvulsants

📦 Product Snapshot

• Brand Name: Zonegran®
• Form: Capsules (25, 50, 100 mg)
• Frequency: Usually twice daily in dogs, once daily in cats

📲 Ask A Vet: Personalized Seizure Management

Managing pet seizures isn’t a one-size-fits-all journey. Use the Ask A Vet app to consult with a licensed veterinarian about Zonisamide, blood test planning, or alternative therapies. Whether you’re just starting or adjusting treatment, expert guidance is just a tap away. Visit AskAVet.com to get started today 📱🐕.

🔚 Final Thoughts

Zonisamide is an excellent seizure control option for pets in 2025, particularly those who don’t respond to standard therapies or who need a milder, well-tolerated add-on. With regular vet oversight and responsible use, it can dramatically improve your pet’s quality of life. Always consult your vet—like Dr Duncan Houston—for a customized treatment plan that meets your pet’s unique needs 🐶❤️.