# Spinosad: veterinary dose and monograph

> Spinosad is a veterinary antiparasitic. Spinosyn (fermentation-derived) oral flea ADULTICIDE giving fast kill and a full month of control in a palatable beef-flavoured chewable — a convenient, water-resistant alternative to topical adulticides. Indications include monthly adult flea control / prevention (dogs and, where licensed, cats); flea-allergy dermatitis management; owners preferring an oral, water-resistant alternative to spot-ons. This monograph lists 2 reference doses for dogs and cats, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/spinosad · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Antiparasitic
- **Also known as:** Comfortis, Trifexis (component)
- **Species with doses:** Dogs and Cats
- **General dose range:** 30–60 mg/kg PO monthly — check the species tables for the indication
- **Routes:** PO
- **Last reviewed:** 1 October 2026

## Indications

- Monthly adult flea control / prevention (dogs and, where licensed, cats)
- Flea-allergy dermatitis management
- Owners preferring an oral, water-resistant alternative to spot-ons
- (Trifexis combination adds milbemycin for heartworm/intestinal worms)

## Spinosad dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

### Dogs

*Spinosad doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Flea control (monthly, with food) | 30–60 mg/kg | PO | monthly | — |

- Flea control (monthly, with food): Papich 5e: 30 mg/kg PO once monthly. Plumb’s p.1073 (Comfortis label): 30–60 mg/kg (minimum 30) PO once monthly with food. Re-dose if vomiting within 1 h. Caution with high-dose ivermectin (interaction).

### Cats

*Spinosad doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Flea control (where licensed) | 50–100 mg/kg | PO | monthly | — |

- Flea control (where licensed): Papich 5e: 50–100 mg/kg PO once monthly (approved dose in some countries 50 mg/kg). Give with food.

## Contraindications

Concurrent high (extra-label) doses of ivermectin/macrocyclic lactones (neurotoxicity risk via P-gp inhibition) — routine heartworm-preventive doses are generally considered safe, but avoid demodicosis-level ivermectin dosing with spinosad. History of seizures (use cautiously). Give with food. Known hypersensitivity.

## Species-specific warnings

> **Caution:** Dogs: Avoid concurrent high-dose ivermectin/macrocyclic-lactone protocols (P-gp inhibition → neurotoxicity), particularly in MDR1-mutant breeds.

## Adverse effects

- Vomiting (the most common effect, especially first dose — give with food)
- Lethargy, decreased appetite, diarrhoea
- Rare: tremor/ataxia/seizure (more likely with concurrent high-dose ivermectin)

## Drug interactions

- High-dose ivermectin / macrocyclic lactones (extra-label, e.g. demodicosis protocols): spinosad inhibits P-gp → increased CNS exposure and neurotoxicity (tremor, seizures) — avoid the combination
- Routine monthly heartworm-preventive macrocyclic-lactone doses: generally considered compatible
- No major other systemic interactions

## Pregnancy and lactation

Considered safe in breeding, pregnant and lactating dogs at label doses (per product data).

## Monitoring

- Flea control over the month; vomiting (especially first dose)
- Review concurrent ivermectin/macrocyclic-lactone use (avoid high doses)
- Neurologic signs if interaction risk

## Toxicity and overdose

Wide margin; the dominant adverse effect is vomiting (give with food). Neurotoxicity is uncommon and chiefly associated with concurrent high-dose ivermectin (P-gp inhibition). Overdose may increase GI signs and, with the ivermectin interaction, CNS signs.

Management: No specific antidote. Supportive care; anti-emetic for vomiting. For neurotoxicity (especially with concurrent high-dose ivermectin): supportive/intensive care, control seizures with benzodiazepines, consider intravenous lipid emulsion. Re-dose flea product only per label if vomiting was early.

## Clinical pearls

- A palatable, water-resistant monthly oral flea killer — great for dogs that swim/bathe or owners who dislike spot-ons
- ALWAYS give with food (absorption) and re-dose if the pet vomits within an hour
- Do NOT pair with high-dose (demodicosis-level) ivermectin — spinosad inhibits P-gp and can precipitate neurotoxicity; routine heartworm-preventive doses are fine
- Vomiting is the usual nuisance effect — feeding with the dose minimises it

## Mechanism of action

Spinosyns activate insect nicotinic acetylcholine receptors at a novel (allosteric) site and also affect GABA-gated channels, causing involuntary muscle contractions, paralysis and rapid death of fleas. The receptor target differs from neonicotinoids/other classes (low cross-resistance). It inhibits mammalian P-glycoprotein, which is the basis of the high-dose ivermectin interaction.

## Formulations and products

- Chewable tablet 30–60 mg/kg (Comfortis) — weight bands
- Comfortis (Elanco) — Spinosad chewable (weight bands), Chewable tablet
- Trifexis (Elanco) — Spinosad + Milbemycin oxime, Chewable (combination)

## Storage

Chewables: 15–30 °C, dry, keep in original packaging away from pets (palatable — risk of accidental over-ingestion).

## Before you use this dose

> **Caution:** Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

## Other antiparasitics

- [Rafoxanide](https://vetmasterji.com/drugs/rafoxanide)
- [Ronidazole](https://vetmasterji.com/drugs/ronidazole)
- [Sarolaner](https://vetmasterji.com/drugs/sarolaner)
- [Selamectin](https://vetmasterji.com/drugs/selamectin)
- [Toltrazuril](https://vetmasterji.com/drugs/toltrazuril)
- [Triclabendazole](https://vetmasterji.com/drugs/triclabendazole)

## Frequently asked questions

### What is the dose of Spinosad for dogs?

Reference doses for Spinosad in dogs: 30–60 mg/kg PO monthly (Flea control (monthly, with food)). Confirm against the label and the patient before use.

### What is the dose of Spinosad for cats?

Reference doses for Spinosad in cats: 50–100 mg/kg PO monthly (Flea control (where licensed)). Confirm against the label and the patient before use.

### When should Spinosad not be used?

Concurrent high (extra-label) doses of ivermectin/macrocyclic lactones (neurotoxicity risk via P-gp inhibition) — routine heartworm-preventive doses are generally considered safe, but avoid demodicosis-level ivermectin dosing with spinosad. History of seizures (use cautiously). Give with food. Known hypersensitivity.

### What are the side effects of Spinosad in animals?

Vomiting (the most common effect, especially first dose — give with food); Lethargy, decreased appetite, diarrhoea; Rare: tremor/ataxia/seizure (more likely with concurrent high-dose ivermectin).

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.