Afoxolaner
Also known as: Nexgard Spectra · Afoxolanerum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Structured calculator evidenceOtodectes synotis infection (extra-label)
Verified clinician required
Alternative schedules — select one
- once
- q1month · for 2 months
NA
Governing clinical context (2)
- ■ Afoxolaner can be administered with or without food.
- Store chewable tablets at or below 30°C (86°F) with excursions permitted up to 40°C (104°F).
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Afoxolaner is an isoxazoline ectoparasiticide used primarily for the treatment and prevention of flea and tick infestations in dogs. It is available as a standalone oral chewable tablet (Nexgard) or in combination with the macrocyclic lactone milbemycin oxime (Nexgard Spectra) for broad-spectrum endo- and ectoparasite control.
Clinical Pearl: Isoxazolines are highly effective but should be used with caution in dogs with a known history of neurological disorders.
Mechanism of action
Afoxolaner acts at ligand-gated chloride channels, in particular those gated by the inhibitory neurotransmitter GABA (gamma-aminobutyric acid).
By binding to these channels, it blocks the pre- and post-synaptic transfer of chloride ions across cell membranes → leading to uncontrolled central nervous system activity → hyperexcitation → death of the insect or acarine parasite.
Safety & warnings
Contraindications
- Known hypersensitivity to afoxolaner or any excipients
Adverse effects
- Vomiting
- Diarrhea
- Lethargy
- Anorexia
- Neurological signs (tremors, ataxia, seizures) - rare
Precautions
Neurological Warning: Use with caution in dogs with a history of seizures or other neurological disorders, as the isoxazoline class has been associated with rare neurological adverse events.
Monitoring
- Efficacy of parasite control
- Adverse gastrointestinal or neurological signs
Pharmacokinetics
Half-life
Absorption
Rapidly absorbed following oral administration. Bioavailability is high (typically >70%).
Distribution
Highly bound to plasma proteins (>99%). Widely distributed to tissues.
Metabolism
Undergoes some hepatic metabolism, but a significant portion is excreted unchanged.
Elimination
Primarily eliminated via biliary excretion into the feces, with a minor renal component.
Overdose
Afoxolaner is generally well tolerated at multiples of the recommended dose. However, significant overdosage may increase the risk of adverse effects, particularly gastrointestinal upset (vomiting, diarrhea) and neurological signs (tremors, ataxia, seizures). Treatment is symptomatic and supportive as there is no specific antidote.
Available products
Formulations
- Oral tablets: 11.3 mg, 28.3 mg, 68 mg, 136 mg (Nexgard)
- Oral tablets: 5 sizes available in combination with milbemycin oxime (Nexgard Spectra)
Veterinary
- Nexgard (11.3 mg, 28.3 mg, 68 mg, 136 mg tablets)
- Nexgard Spectra (afoxolaner + milbemycin oxime tablets)
Regulatory status
POM-V
POM-V
No regulatory data for: 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store in the original blister packaging to protect from light and moisture. Keep out of reach of children and animals.
Client information
Administer the chewable tablet orally once a month, or as directed by your veterinarian. It can be given with or without food.
Monitor your dog for any signs of stomach upset, such as vomiting or diarrhea.
Important: Contact your veterinarian immediately if your dog experiences muscle tremors, uncoordinated movements, or seizures after taking this medication.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.