Afoxolaner in focus: one isoxazoline, one adverse-event database, one market authorisation
Most drug-safety writing compares classes of molecules. This article does the opposite: it follows a single active ingredient — afoxolaner, the molecule inside NexGard — through three different regulatory lenses and asks what each jurisdiction actually records about it. Afoxolaner is an isoxazoline-class ectoparasiticide: it blocks insect and acarine GABA- and glutamate-gated chloride channels, killing fleas and ticks. In the United States it lands in the FDA Center for Veterinary Medicine's adverse-event database; in Canada it holds a market-authorisation (DIN) number; in the EU it sits inside the EMA's antiparasitic medicine review. The same molecule, three paper trails — and, as we will see, the trails do not all describe the same thing.
Lens 1 — The US adverse-event database
The ade_afoxolaner_adverse_events topic is built from the FDA CVM openFDA animalandveterinary/event.json endpoint, pulled 2026-07-21. Afoxolaner's cumulative total is 69037 reports. The species split is overwhelmingly canine:
- Dog 63981
- Human 92
- Cat 82
- Other 3
- Other Canids 3
- (unrecorded species) 2
The top reported reactions, in VEDDRA terms, are:
- Vomiting 15987
- Diarrhoea 6128
- Lethargy (see also Central nervous system depression in 'Neurological') 5710
- Lack of efficacy (ectoparasite) - tick NOS 4991
- Lack of efficacy (ectoparasite) - flea 4532
- Seizure NOS 4406
- Lack of efficacy (bacteria) - Borrelia 3554
- Lack of efficacy (tick) 3389
- Skin disorders NOS 2626
- Lack of efficacy (bacteria) - NOS 2606
Two disclaimers govern every number above, and they matter more than the totals. First, reported ≠ causal. These are spontaneous, passive-surveillance reports submitted by veterinarians, owners and manufacturers; the count proves a report was filed, not that the drug caused the event. Second, the "Lack of efficacy" terms are product-performance reports, not adverse reactions. "Lack of efficacy (ectoparasite) - tick/flea" and "Lack of efficacy (bacteria) - Borrelia" denote the product failing to kill the parasite — they must not be read as toxicity in the animal. Stripping those out, the genuine clinical-reaction signal is led by gastrointestinal and neurological terms: Vomiting 15987, Diarrhoea 6128, Lethargy 5710, and Seizure NOS 4406. That seizure count is the same class-wide neurological signal seen across the other isoxazolines. The source also notes the counts are report-level — one report may list multiple reactions and multiple animals, so the figures are not additive and do not imply causation.
Lens 2 — The Canadian market authorisation
The approval_label_nexgard topic records afoxolaner's Canadian registration as a verbatim Health Canada Drug Product Database (DPD) row:
Marketed,02427435,Dogs,BOEHRINGER INGELHEIM ANIMAL HEALTH CANADA INC.,NEXGARD,Veterinary,Yes,PRESCRIPTION,1,AFOXOLANER,11.3 MG
Reading the fields: the product is Marketed under DIN 02427435, species Dogs, holder Boehringer Ingelheim Animal Health Canada Inc., class Veterinary, PRESCRIPTION, active ingredient AFOXOLANER at 11.3 MG, annotated as an oral ectoparasiticide. This is the "approved and on the shelf" leg of the dossier: it tells you the molecule is authorised, for which species, at what strength, and that it requires a prescription. What it does not contain is the product monograph — indications, contraindications and full dosing "reside in the product monograph, which is not contained in the DPD registration CSV". So the Canadian label answers "is it authorised, and at what strength?", not "how safe is it in practice?".
Lens 3 — The EU antiparasitic review (and an honest gap)
The eu_ema_qp_antiparasitics_pet topic reviews the EMA's centrally authorised QP-class (antiparasitic) pet medicines from the dataset generated 20/07/2026. Here the dossier hits a wall worth stating plainly: afoxolaner / NexGard is not listed in this EU topic. The QP pet ectoparasiticides captured are Comfortis (spinosad, Dogs;Cats), Activyl Tick Plus (indoxacarb;permethrin, Dogs), ProMeris (metaflumizone, Cats), ProMeris Duo (metaflumizone;amitraz, Dogs), Certifect (fipronil/amitraz/(S)-methoprene, Dogs), Cheristin (Cats), plus endectocides Longrange (eprinomectin, Cattle, Refused) and Trifexis (spinosad;milbemycin oxime, Dogs, Expired). The topic's own summary states "Most carry Withdrawn or Application withdrawn status."
So the EU leg of this single-drug dossier is a class-context leg, not a direct afoxolaner entry. The honest reading: as captured in the EMA centralised database slice, the flea/tick brands that carry an EMEA/V/C/... number are predominantly Withdrawn or Application-withdrawn — and afoxolaner/NexGard is absent from that particular centrally-authorised list. That absence is itself informative: it means afoxolaner's EU presence, if any, would run through a different authorisation route (national or a centrally-authorised number not captured in this topic) rather than the withdrawn legacy entries documented here. We do not fill the gap with assumption.
What the three lenses add up to
Put the three paper trails together and a single molecule resolves into three different kinds of fact:
- The US records outcomes after use. 69,037 cumulative reports, overwhelmingly canine, with a clinical-reaction profile led by Vomiting (15987), Diarrhoea (6128), Lethargy (5710) and Seizure NOS (4406) — but filtered through the "reported ≠ causal" and "lack-of-efficacy ≠ adverse-reaction" caveats.
- Canada records the authorisation. DIN 02427435, Dogs, AFOXOLANER 11.3 MG, PRESCRIPTION — a clean statement that the product is marketed and at what strength, with the monograph held separately.
- The EU records the class, not this molecule. The captured QP antiparasitic review documents competing ectoparasiticides (spinosad, metaflumizone, fipronil, indoxacarb, eprinomectin, milbemycin oxime) — none of them afoxolaner — and most in Withdrawn/Application-withdrawn status.
The takeaway for a clinician or owner is that "what the regulators know about afoxolaner" is fragmented by design. The adverse-event surveillance lives in the US database; the market-authorisation fact lives in the Canadian DIN; and the EU, in the slice available here, tells you about the ectoparasiticide category afoxolaner belongs to rather than about afoxolaner itself. None of the three, on its own, answers "is this drug safe for my dog?" — and crucially, the largest number in the dossier (69,037) is a report count, not a verdict.
Sources
Every figure above is a verbatim substring of one of the following source topics (all confirmed present on disk):
ade_afoxolaner_adverse_events— afoxolaner total 69037; Dog 63981, Human 92, Cat 82, Other 3, Other Canids 3; top reactions Vomiting 15987, Diarrhoea 6128, Lethargy 5710, Seizure NOS 4406, plus Lack-of-efficacy terms (product-performance, not ADR); openFDA pulled 2026-07-21; counts report-level, not additive, not causal.approval_label_nexgard—Marketed,02427435,Dogs,BOEHRINGER INGELHEIM ANIMAL HEALTH CANADA INC.,NEXGARD,Veterinary,Yes,PRESCRIPTION,1,AFOXOLANER,11.3 MG; DIN 02427435; oral ectoparasiticide; monograph not in DPD CSV.eu_ema_qp_antiparasitics_pet— QP pet ectoparasiticides (Comfortis/Activyl Tick Plus/ProMeris/ProMeris Duo/Certifect/Cheristin/Longrange/Trifexis); afoxolaner/NexGard not listed in this topic; most entries Withdrawn / Application withdrawn (dataset 20/07/2026).