Vet Guide to Comfortis® (Spinosad) in 2025 🐾

Hello, I’m Dr Duncan Houston, BVSc—founder of Ask A Vet. In this updated 2025 guide, we dive into Comfortis®, a chewable spinosad tablet approved for dogs and cats to treat and prevent flea infestations. We’ll explore how it works, proper dosing, expected results, side effects, and veterinary-safe use to help keep your pet & home flea-free. 🐶🐱

📘 What Is Comfortis®?

Comfortis® is an FDA-approved monthly chewable medication containing the active ingredient spinosad, designed to treat and prevent flea infestations in dogs and cats 14 weeks and older. It kills adult fleas rapidly and protects against reinfestation for a full month :contentReference[oaicite:3]{index=3}.

✅ How Comfortis® Works

Spinosad targets a flea's nervous system, causing paralysis and death within 30 minutes to 4 hours. In efficacy trials, Comfortis® killed 100% of fleas on dogs and 98% on cats within four hours of dosing :contentReference[oaicite:4]{index=4}.

📐 Dosing Instructions

• **Dogs & Puppies (≥14 weeks, ≥5 lb / 2.3 kg):** Monthly chewable tablet—dose varies by weight (140–1,620 mg) :contentReference[oaicite:5]{index=5}.
• **Cats & Kittens (≥14 weeks, ≥4.1 lb / 1.9 kg):** Same weight-based dosing in chewable tablets :contentReference[oaicite:6]{index=6}.
• Administer **with food** to maximize efficacy and reduce vomiting risk :contentReference[oaicite:7]{index=7}.
• **Missed Dose:** Give as soon as remembered, then resume monthly schedule. If vomiting occurs within an hour, redose with food :contentReference[oaicite:8]{index=8}.

⏱️ Onset & Duration

Comfortis® starts killing fleas as early as **30 minutes**, reaching full effect in **4 hours**, and provides continuous protection for **30 days** :contentReference[oaicite:9]{index=9}.

⚠️ Side Effects & Safety

Common side effects:

• Vomiting—take with a meal to reduce occurrence :contentReference[oaicite:10]{index=10}
• Possible mild lethargy, diarrhea, lack of appetite, increased thirst, incoordination, coughing :contentReference[oaicite:11]{index=11}

Uncommon/severe reactions:

• Seizures—especially in dogs already prone to epilepsy or those receiving high-dose ivermectin concurrently :contentReference[oaicite:12]{index=12}

Use with caution in breeding female dogs and in pets with pre-existing seizure disorders :contentReference[oaicite:13]{index=13}.

🚫 Contraindications & Interactions

• Not evaluated in pregnant or lactating cats—use only if benefit outweighs risk :contentReference[oaicite:14]{index=14}.
• Avoid concurrent use with high-dose ivermectin—can lead to neurologic symptoms :contentReference[oaicite:15]{index=15}.
• Ensure vet is aware of all supplements, medications, and health conditions before use :contentReference[oaicite:16]{index=16}.

🧪 Monitoring & When to Contact Vet

• Watch for vomiting or lethargy—especially after first dose.
• If seizures, incoordination, or persistent illness occur—seek veterinary care.
• No routine bloodwork needed, but follow vet advice if your pet is elderly or has chronic health issues.

🏡 Real-World Scenarios

🐶 Dog with Flea Allergy Dermatitis

• Start Comfortis® monthly with food.
• Combine with flea allergy management: topical shampoos, antihistamines, and home environment control.
• Expect itch and skin improvement within 1–2 months.

🐱 Multi-Pet Household

• Treat all dogs and cats to break flea lifecycle.
• Wash bedding and vacuum regularly; use environmental sprays if infestation persists.

❓ Frequently Asked Questions

Does Comfortis® kill ticks?

No—Comfortis® only targets fleas. For tick protection, consult your vet for additional products.

Can I give it year-round?

Yes—year‑round use is best in most regions, especially with flea allergy or heavy infestation risk.

Is the chewable tablet okay for cats?

Yes—but some cats may dislike the flavor or size; hide in food or use pill pockets as needed :contentReference[oaicite:17]{index=17}.

Is it safe for senior pets?

Generally yes—just monitor for side effects and inform your vet about any health issues :contentReference[oaicite:18]{index=18}.

📌 Final Takeaways

• Comfortis® (spinosad) is a fast-acting, once-monthly oral chew for flea control in dogs and cats.
• Administer with food; redose if vomiting occurs within an hour.
• Common side effects—gentle vomiting or GI upset; rare but serious reactions like seizures in sensitive individuals.
• Avoid high-dose ivermectin combinations; use caution in epileptics and pregnant cats.
• Use within a complete flea-control plan—treat all pets and environment for best results.

Ready to protect your pet from fleas with Comfortis®? Download the Ask A Vet app for dosing reminders, symptom tracking, and 24/7 access to veterinary guidance. Let’s keep your home & pets flea-free together! 🐾❤️