Ivermectin and selamectin are both macrocyclic lactones, but their US labels are not interchangeable: the FDA-approved ivermectin products for dogs are labeled around heartworm prevention and intestinal worms, while the selamectin label (Revolution, Zoetis Inc., published on DailyMed) adds flea, ear mite, sarcoptic mange and one tick claim that no ivermectin label carries. The comparison that matters is never "which drug is stronger" — it is which parasite, in which species, appears in which approved indication. A good starting point is the index of FDA-approved ivermectin animal products, which lists what each formulation is actually cleared to do.

Every product named here is an animal drug, labeled for animal use only, and none of them is approved for people. FDA states plainly in its consumer update dated 5 April 2024 that animal ivermectin products are different formulations from those approved for humans, that their safety in humans is not known, and that medications intended for animals should never be used on people. All label and guideline facts below were verified against primary sources on or before 28 September 2026.

Key takeaways

  • Ivermectin, moxidectin, selamectin, eprinomectin and doramectin are all macrocyclic lactones — swapping among them is a change of product, not a change of drug class.
  • Fenbendazole (a benzimidazole), pyrantel and morantel (tetrahydropyrimidines) and praziquantel (an isoquinoline) act differently and carry different label claims; praziquantel is the tapeworm component in equine and canine combination products.
  • Among the FDA-approved ivermectin labels reviewed for this article, none carries a flea or tick indication. Where an ivermectin-containing product treats fleas, the flea claim comes from the other active ingredient.
  • US surveys tell very different resistance stories by species: AAEP (May 2024) records only "early indications" of macrocyclic lactone resistance in equine cyathostomins, while ACSRPC (June 2024) reports that most barber pole worm populations in temperate US sheep, goats and camelids are already ivermectin-resistant.
  • These are animal formulations only. Product choice belongs with a veterinarian and, for worms, with a fecal egg count reduction test rather than a label read in isolation.

Drug classes in one paragraph: macrocyclic lactones, benzimidazoles, tetrahydropyrimidines, isoquinolines

Two plain equine paste syringes on a tack room shelf, representing the difference between ivermectin and moxidectin.

The FDA-approved STROMECTOL label (SPL dated 20 September 2024) calls ivermectin a semisynthetic anthelmintic derived from the avermectins; FDA-approved ivermectin injection labels for animals call it "a member of the macrocyclic lactone class of endectocides." The AAEP Internal Parasite Control Guidelines (May 2024 revision) state that macrocyclic lactones act on glutamate-gated chloride channels in nematode nerve and muscle cells, producing flaccid paralysis, and Table 1 of that document lists the class (ivermectin, moxidectin) with general label claims for cyathostomins, large strongyles, ascarids, pinworms, threadworms and bots. The American Consortium for Small Ruminant Parasite Control (ACSRPC) describes three dewormer chemical classes available in the United States — benzimidazole, membrane depolarizing, and macrocyclic lactone — with ivermectin in the third. Benzimidazoles (fenbendazole, albendazole, oxfendazole) and the tetrahydropyrimidines (pyrantel, morantel) are gut-active nematode drugs; praziquantel, an isoquinoline, is the cestode drug, and the Droncit (praziquantel) label on DailyMed describes it as a cestocide for removal of tapeworms in dogs and cats.

Ivermectin and moxidectin: same class, different spectrum and safety margin

Owner parting a dog's fur at the shoulders to apply a topical spot-on parasiticide at home.

Moxidectin is the other macrocyclic lactone in common US use — Quest (moxidectin) equine oral gel is an OTC animal drug label on DailyMed for horses and ponies including breeding mares and stallions. AAEP reports that in the 1990s moxidectin egg reappearance periods ran 12–16 weeks against ivermectin's 8–10 weeks, but that since 2017 several studies have reported ERPs of 4–5 weeks for both drugs. AAEP also cautions that a shortened ERP is not necessarily a sign of emerging resistance; selection for parasites with shorter life cycles may explain part of it.

Encysted larvae and withdrawal times

AAEP names moxidectin and fenbendazole as the two anthelmintics with registered efficacy against encysted cyathostomin larvae, describes ivermectin as non-larvicidal, and states that neither moxidectin nor fenbendazole can be expected to perform with high larvicidal efficacy — recent studies show both reduce encysted burdens by less than 85%. In small ruminants the practical difference is residue timing: the ACSRPC goat chart (November 2024) gives oral ivermectin at 0.4 mg/kg with a 20-day meat and 20-day milk withdrawal, and oral moxidectin sheep drench at 0.4 mg/kg with a 23-day meat and 19-day milk withdrawal for a single dose. ACSRPC states these are FARAD-derived extra-label recommendations, not FDA label withdrawal periods.

Selamectin: what the topical label claims that ivermectin's does not

A dog being combed on a farmhouse porch during a flea and tick check.

The Revolution (selamectin) label states that it kills adult fleas and prevents flea eggs from hatching for one month, and is indicated for prevention and control of flea infestations (Ctenocephalides felis), prevention of heartworm disease caused by Dirofilaria immitis, and treatment and control of ear mite (Otodectes cynotis) infestations; in dogs it is also indicated for treatment and control of sarcoptic mange (Sarcoptes scabiei) and for control of tick infestations due to Dermacentor variabilis.

No single ivermectin product assembles that list. HEARTGARD tablets (NADA 138-412, 68 micrograms ivermectin) and HEARTGARD Chewables (NADA 140-886) are indicated to prevent heartworm disease by eliminating the tissue stage of D. immitis larvae for 30 days after infection, per 21 CFR 520.1193 — a point worth reading alongside how monthly heartworm preventives are labeled. Ear mites in cats get a separate ivermectin product, ACAREXX otic suspension (NADA 141-174, a 0.5 mL tube of 0.01 percent suspension, 21 CFR 524.1195). Fleas require a second molecule entirely: Advantage DUO (NADA 141-208, 21 CFR 524.1140) pairs ivermectin with 100 mg/mL imidacloprid.

Pyrantel and praziquantel: why combination products exist

A veterinarian examining a fecal sample under a microscope in a rural clinic while a producer waits.

Combination labels exist because the ivermectin claim stops where the other drug's claim starts. HEARTGARD Plus (NADA 140-971) supplies 68 mcg ivermectin with 57 mg pyrantel, 136 mcg with 114 mg, or 272 mcg with 227 mg, and its indication adds treatment and control of roundworms (Toxocara canis, Toxascaris leonina) and hookworms (Ancylostoma caninum, Uncinaria stenocephala) — claims that come from the pyrantel. Generic equivalents include IVERHART PLUS (ANADA 200-302) and Tri-Heart Plus (ANADA 200-338). Standalone pyrantel products such as Nemex-2 suspension are labeled for removal of the same roundworms and hookworms in dogs and puppies. None of the ivermectin/pyrantel dog combinations carries a whipworm claim.

Praziquantel is added for tapeworms. ZIMECTERIN GOLD (NADA 141-214) contains 1.55% ivermectin and 7.75% praziquantel, dosed at 200 mcg/kg ivermectin plus 1 mg/kg praziquantel in a syringe treating one 1,250 lb horse, and its indication adds Anoplocephala perfoliata; EQUIMAX (NADA 141-215) pairs 1.87% ivermectin with 14.03% praziquantel in a syringe treating up to 1,320 lb. For dogs, IVERHART MAX Chew (NADA 141-441) combines ivermectin, pyrantel pamoate and praziquantel. AAEP recommends including praziquantel for tapeworms at least once a year where horses have access to green pastures — while also reporting data suggesting treatment failure of praziquantel and pyrantel pamoate against A. perfoliata in Central Kentucky.

Fenbendazole: where it covers what ivermectin does not

The clearest canine example of how fenbendazole and ivermectin differ is on the Panacur C (fenbendazole) label, which is for treatment and control of roundworms (Toxocara canis, Toxascaris leonina), hookworms (Ancylostoma caninum, Uncinaria stenocephala), whipworms (Trichuris vulpis) and tapeworms (Taenia pisiformis). Whipworms and T. pisiformis are exactly the gaps in the ivermectin/pyrantel labels. Panacur Plus (NADA 141-286, 21 CFR 520.1200) exists for that reason, combining ivermectin, fenbendazole and praziquantel in one chewable tablet.

The coverage runs the other way too. The Safe-Guard (fenbendazole) 10% suspension label covers lungworms, stomach worms and intestinal worms in cattle, but fenbendazole carries no external-parasite claims, whereas the IVOMEC Injection label (NADA 128-409) includes sucking lice and mange mites alongside gastrointestinal roundworms and cattle grubs. In goats, the ACSRPC chart gives fenbendazole at 10 mg/kg with a 16-day meat and 12-day milk withdrawal; AAEP recommends the benzimidazole class for the two foal ascarid treatments at about 2–3 months and about 5 months of age, at a labeled dose of 10 mg/kg orally.

Fleas and ticks: no ivermectin label claims them, and what does

Searches for ivermectin for fleas on dogs, or ivermectin for ticks, run into a label problem. Across the FDA-approved ivermectin labels examined for this article, the arthropod claims are lice, mange mites, grubs, nasal bots, equine bots and ear mites — IVOMEC Pour-On (NADA 140-841, 5 mg ivermectin per mL, 1 mL per 22 lb) is the one cattle form that adds horn flies (Haematobia irritans) and the biting louse Damalinia bovis. Fleas and ticks do not appear. FDA has also issued Emergency Use Authorizations for ivermectin products against New World screwworm — Ivomec injection for cattle on 5 February 2026, Ivermectin Liquid for Horses on 15 July 2026, and Bimectin injection for cattle on 27 August 2026 — but those authorizations cover a fly larva, not fleas or ticks.

What does carry those claims: selamectin, for fleas and D. variabilis; Revolution Plus, where the added sarolaner brings a broader tick list including Amblyomma americanum and Amblyomma maculatum in cats; and imidacloprid, the flea component in Advantage DUO.

Comparison table by parasite and species, from the labels

Target Ivermectin label Comparator label
Heartworm prevention, dogs HEARTGARD/HEARTGARD Chewables: prevents heartworm disease by eliminating the tissue stage of D. immitis larvae for 30 days after infection (21 CFR 520.1193) Revolution: prevention of heartworm disease caused by D. immitis
Fleas, dogs and cats No flea claim on the ivermectin labels reviewed; Advantage DUO's flea activity is attributed to imidacloprid Revolution: kills adult fleas, prevents eggs hatching for one month
Ticks No tick claim found on the ivermectin labels reviewed Revolution: control of Dermacentor variabilis; Revolution Plus adds sarolaner for further tick species in cats
Whipworms, dogs Not claimed by the ivermectin/pyrantel combinations Panacur C: whipworms (Trichuris vulpis)
Tapeworms, horses ZIMECTERIN (1.87% paste, NADA 134-314) alone does not claim tapeworms ZIMECTERIN GOLD and EQUIMAX add praziquantel for A. perfoliata
Encysted small strongyles, horses AAEP describes ivermectin as non-larvicidal Moxidectin and fenbendazole have registered efficacy, but AAEP reports both reduce burdens by less than 85%
Cattle lice and mange mites IVOMEC Injection indication includes sucking lice and mange mites; 35-day slaughter withdrawal Safe-Guard fenbendazole: internal parasites only
Goats No FDA-approved ivermectin product lists goats (Animal Drugs @ FDA, retrieved 28 September 2026) ACSRPC notes only fenbendazole at 5 mg/kg and morantel tartrate are FDA-approved in goats among the drugs on its chart

Rotation: why two drugs from the same class are not a rotation

AAEP's position on the old calendar is unhedged. Its take-home messages tell owners to "discontinue deworming all horses with fixed intervals year-round (e.g., every 2 months), and stop blindly rotating anthelmintic classes," and its closing list of six changes worth making includes "abandon rotational deworming." Alternating ivermectin and moxidectin is not a rotation at all: both are macrocyclic lactones, and AAEP now records the same 4–5 week ERP for each. ACSRPC puts the same warning in mechanistic terms — moxidectin will kill ivermectin-resistant worms for a while, but used against ivermectin-resistant worms, resistance levels climb over several grazing seasons until moxidectin loses effectiveness.

The two species groups diverge on combinations. ACSRPC recommends combination treatment for clinically parasitized small ruminants, usually albendazole plus moxidectin plus levamisole in the US, given as full separate doses and never mixed in one syringe, with the withdrawal set by the longest-withdrawal component. AAEP, by contrast, states it currently lacks evidence to endorse combination deworming as a sustainable approach for strongyle control in horses, and says the off-label use in horses of anthelmintics labeled for other species, such as ruminants, is inappropriate and not recommended — worth remembering when building a horse deworming program.

Resistance: what US surveys have found, by species

In horses, AAEP's Table 4 (May 2024) records macrocyclic lactone resistance as "early indications" in cyathostomins but "widespread" in pinworms and in Parascaris spp., where widespread is defined as reported on multiple continents with farm prevalences often above 80%. AAEP advises assuming benzimidazole and pyrantel resistance in strongyles until proven otherwise by testing, which it says leaves macrocyclic lactones as the only option in many locations, and assuming macrocyclic lactone resistance in ascarids until documented otherwise.

In small ruminants the picture is worse, which is the background to resistance in small ruminants. ACSRPC states that most barber pole worm populations from sheep, goats and camelids in temperate parts of the United States are already resistant to ivermectin, with moxidectin resistance becoming more common. Its resistance factsheet (November 2024) cites a Mid-Atlantic study of 14 sheep and 20 goat farms in 2008–2009 finding ivermectin resistance on 82 percent of farms and moxidectin resistance on 47 percent, and a more recent Maryland, Virginia and Georgia sheep survey finding benzimidazole, ivermectin, moxidectin and levamisole resistance on 100%, 97%, 83% and 50% of farms respectively. For dogs and cats, the verified source set behind this article contains no US survey figure, so none is given here. FDA-approved livestock labels carry their own warning: the IVOMEC Injection label states that parasite resistance may develop to any dewormer and has been reported for most classes of dewormers.

Why the right comparison is made with a veterinarian and a fecal test

A label tells you what a product is cleared to claim; only testing tells you whether it still works on your animals. AAEP's first take-home message is to perform fecal egg count reduction tests annually in every herd or barn, with a pragmatic rule of thumb that any anthelmintic should reduce both ascarid and strongyle fecal egg counts by more than 95% at 14 days after treatment. ACSRPC uses a comparable standard for small ruminants — a reduction of 95 percent or more, measured on 10 or more treated animals with counts of 250 epg or higher, with the post-treatment count taken 7 to 14 days after deworming at least once a year.

A veterinarian is also the person who resolves conflicts in the guidance itself. Two ACSRPC documents both dated November 2024 give different milk withdrawals for oral ivermectin in goats — 20 days on the goat chart, 9 days on the dairy goat page — and ACSRPC separately warns that outdated versions of its charts circulate online. Because no FDA-approved ivermectin product lists goats at all, any such use is extra-label and belongs under veterinary direction. And again: all of these are animal drugs, labeled for animal use only and not approved for people.

Frequently asked questions

Is selamectin just topical ivermectin?

No. Both are macrocyclic lactones, but they are different molecules with different approved labels. The selamectin label claims fleas, heartworm prevention, ear mites, sarcoptic mange and Dermacentor variabilis ticks; the ivermectin dog labels are built around heartworm prevention, with intestinal worm claims supplied by added pyrantel.

If ivermectin has stopped working, should I switch to moxidectin?

That is a veterinary decision, and it is not a class change. ACSRPC states moxidectin will kill ivermectin-resistant worms for a while, but that using it against them drives resistance up over several grazing seasons until moxidectin also fails. AAEP recommends confirming efficacy with a fecal egg count reduction test rather than assuming.

Does ivermectin kill fleas or ticks on dogs?

No FDA-approved ivermectin label examined for this article carries a flea or tick indication. Flea activity in an ivermectin-containing product such as Advantage DUO is attributed to imidacloprid, the other active ingredient.

Is fenbendazole better than ivermectin for dogs?

Neither is "better" in general; they cover different parasites. The Panacur C label claims whipworms and Taenia pisiformis, which ivermectin/pyrantel products do not, while ivermectin products carry the heartworm prevention claim that fenbendazole does not.

Can I use a cattle or sheep ivermectin product in another species?

Labels say no. The IVOMEC Injection label states the product was developed for cattle, swine, reindeer and American bison only, and warns that use in other species may cause severe adverse reactions, including fatalities in dogs. AAEP says using ruminant-labeled anthelmintics in horses is inappropriate. All of these products are for animal use only and are not approved for human use.

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