Ivermectin

What is this medication for?

• Heartworm prevention (FDA-approved); microfilaricide, slow-kill adulticide adjunct, demodicosis (higher doses)
• Heartworm prevention (FDA-approved)

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

• Never substitute large-animal (cattle/horse) injectable ivermectin formulations for small-animal dosing without extremely careful dilution/calculation — this is a well-documented, sometimes fatal, dosing-error scenario.

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• Vomiting, wobbliness/unsteadiness, low energy/tiredness (Overdose)

Worth a phone call to your veterinarian

• Shock-like reaction (microfilaricide use) — depression, hypothermia, vomiting (Uncommon, related to dying microfilariae)

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Neurotoxicity: hypersalivation, depression, wobbliness/unsteadiness, blindness, coma (Dose- and breed-dependent)
• Retinopathy (sudden blindness/mydriasis, usually reversible) (High-dose only)

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: Public-health/label restriction — not for use in lactating dairy animals; not recommended in puppies <6 weeks old
• has or has had: ABCB1-1Δ (formerly MDR1) mutant breeds — Collies, Australian Shepherds, Shelties, Old English Sheepdogs, long-haired Whippets — at higher risk of CNS toxicity at doses above the heartworm-prevention range; genetic testing recommended before high-dose (e.g., demodicosis) use in these breeds

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • P-glycoprotein inhibitors (ketoconazole, itraconazole, cyclosporine, diltiazem, verapamil, erythromycin, clarithromycin, spironolactone, amiodarone, quinidine, tamoxifen, carvedilol)
  • Benzodiazepines
  • Spinosad (Comfortis)

Storage and handling

Tightly sealed container, protect from light, room temperature.

Good to know

• Never substitute large-animal (cattle/horse) injectable ivermectin formulations for small-animal dosing without extremely careful dilution/calculation — this is a well-documented, sometimes fatal, dosing-error scenario.
• At the low heartworm-prevention dose, even ABCB1-mutant dogs are generally considered safe to treat — the major risk arises at the much higher off-label doses (e.g., demodicosis, aggressive microfilaricide protocols).
• Combined with doxycycline pre-treatment (10 mg/kg BID × 4 weeks) as part of the "moxi/doxy" or slow-kill heartworm adulticide protocol per American Heartworm Society guidance.