Afoxolaner
**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: 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.
Dosing by species
- Parasite control (fleas, ticks) · 11.3 mg, 28.3 mg, 68 mg, or 136 mg tablets · PO · Not specified in monograph · Not specified · Administer appropriate tablet size based on weight. Available alone (Nexgard) or with milbemycin oxime (Nexgard Spectra).
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Known hypersensitivity to afoxolaner or any excipients
Adverse effects
- Vomiting
- Diarrhea
- Lethargy
- Anorexia
- Neurological signs (tremors, ataxia, seizures) - rare
Monitoring
- Efficacy of parasite control
- Adverse gastrointestinal or neurological signs
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.
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.