Stronghold (Selamectin) for Cats & Dogs: Complete Guide – How It Works, Full Parasite Coverage, Colour-Coded Dosage, the 2-Hour Water Rule & How It Compares to Frontline and Advocate

Stronghold is one of the most versatile parasite control products in veterinary medicine. Unlike most flea spot-ons that target only external parasites, Stronghold’s active ingredient selamectin is absorbed systemically and works against fleas, heartworm larvae, ear mites, roundworms, hookworms, biting lice, and sarcoptic mange from a single monthly application. This guide covers everything: the mechanism, full parasite coverage list, colour-coded dosage for every size cat and dog, critical safety rules, and a direct comparison with Frontline and Advocate.

Stronghold = Revolution: The Same Product with a Different Name

If you’ve arrived here searching for Revolution, you’re in the right place. Stronghold (Europe/UK/Australia) and Revolution (USA/Canada) are identical products — same active ingredient (selamectin), same manufacturer (Zoetis), same concentrations, same pipette colours, same indications. The only difference is the brand name used in each market. International veterinary pharmacies typically stock the European Stronghold formulation, which is bioequivalent to the US Revolution.

What Is Selamectin and How Does It Work?

Selamectin is a semi-synthetic macrocyclic lactone — the same drug class as ivermectin and milbemycin, but with a distinct chemical structure and importantly a proven safe profile in ivermectin-sensitive Collie breeds at up to 5× the recommended dose.

The Chloride Channel Mechanism

Selamectin works by binding selectively to glutamate-gated chloride ion channels — a type of ion channel found in invertebrate nerve and muscle cells (insects, mites, and nematode worms) that simply does not exist in mammalian cells. By locking these channels permanently open, selamectin floods the parasite cell with chloride ions, causing hyperpolarisation — a state of electrical over-inhibition that permanently paralyses and kills the organism.

Because these specific chloride channels are absent in mammalian nervous systems, selamectin’s toxic effect is highly selective for the target invertebrate parasites. This explains the extremely wide safety margin — no adverse effects were seen at 10× the recommended dose in healthy dogs, and at 5× the dose in ivermectin-sensitive Collies.

Systemic Distribution After Spot-On Application

After application to the skin at the back of the neck, selamectin is absorbed transdermally and enters the systemic circulation. Peak plasma concentrations are reached approximately 1 day after application in cats and 3 days in dogs. Once in the bloodstream, selamectin distributes into the skin, sebaceous glands, and tissues throughout the body.

The terminal elimination half-life is 8 days in cats and 11 days in dogs. This slow clearance means selamectin remains at detectable protective concentrations in plasma for the full 30-day inter-dose interval, providing continuous systemic protection against heartworm larvae and other systemic parasites throughout the month.

Full Parasite Coverage: What Stronghold Treats and Prevents

Fleas — Triple-Mechanism Full Lifecycle Control

Stronghold kills fleas at three life stages, making it more comprehensive than many competing spot-ons that only target adult fleas:

• Adulticidal: Kills adult fleas (Ctenocephalides spp.) on the animal. Adult fleas begin dying within hours of selamectin contact.
• Ovicidal: Prevents flea eggs laid on the treated animal from hatching. Ovicidal activity persists for 3 weeks after each application. Eggs that fall into the environment from the treated animal are also non-viable.
• Larvicidal: Shed skin cells and hair from selamectin-treated animals contain selamectin residues that kill flea larvae in the pet’s environment (bedding, carpets, furniture). Even flea larvae that have not been directly exposed to the treated animal are killed by contact with this debris.

The combination of all three mechanisms breaks the entire flea lifecycle — treating the animal AND controlling the environmental reservoir simultaneously. Frontline (fipronil) kills adult fleas and combined with S-methoprene (in Frontline Combo) inhibits egg development, but it lacks Stronghold’s direct larvicidal action on environmental flea populations.

Heartworm Prevention — Stronghold’s Most Distinctive Feature

Heartworm disease (Dirofilaria immitis) is transmitted by mosquitoes. When an infected mosquito bites a treated animal, the heartworm larvae in the mosquito’s saliva enter the bloodstream — where selamectin at systemic concentrations kills them before they can develop into adult worms. Monthly administration maintains selamectin above the minimum effective concentration throughout the inter-dose period.

This is the single biggest differentiator between Stronghold and the majority of competitor spot-ons. Frontline (fipronil), Seresto collar, and Bravecto do not prevent heartworm. In heartworm-endemic regions — Mediterranean Europe, the Americas, Asia, Africa, and Australia — using a product without heartworm prevention leaves a significant gap in parasite protection.

Critical note: Selamectin kills heartworm larvae (L3/L4 stages) but does NOT kill adult heartworms already established in the heart and pulmonary arteries. Before starting any heartworm prevention programme, animals over 6 months of age in endemic regions should be tested for existing adult heartworm infection. Starting prevention on an animal with an undetected adult heartworm infection does not treat it.

Ear Mites (Otodectes cynotis)

Applied to the back of the neck (not the ear), Stronghold’s systemically absorbed selamectin reaches the skin and ear canal tissue. A single dose typically resolves ear mite infestations in both cats and dogs. In dogs, a veterinary re-examination 30 days after treatment is recommended, as some animals require a second dose. Gently remove visible debris from the external ear canal at the time of treatment — do not use this as an alternative to eradicating the mites, just to improve comfort and visibility.

Roundworms, Hookworms, and Biting Lice (Cats)

In cats, a single Stronghold application treats adult intestinal roundworms (Toxocara cati) and adult hookworms (Ancylostoma tubaeforme), as well as biting lice (Felicola subrostratus). This makes Stronghold one of the most cost-effective and convenient cat parasite products available — addressing flea control, heartworm prevention, internal worms, and lice in one pipette.

Roundworms, Biting Lice, and Sarcoptic Mange (Dogs)

In dogs, Stronghold treats adult intestinal roundworms (Toxocara canis) and biting lice (Trichodectes canis) with a single dose. For sarcoptic mange (caused by Sarcoptes scabiei — one of the most intensely itchy skin conditions in dogs), two consecutive monthly treatments are required. The first dose kills the adult mites; the second dose addresses eggs that hatched into new adults after the first treatment. One dose is insufficient for reliable mange clearance.

Complete Colour-Coded Dosage Guide

Dose: minimum 6mg selamectin per kg body weight per application. Apply the full pipette contents to the skin at the base of the neck once monthly.

Cats

Dogs

The Three Critical Application Rules

1. Keep Away From Flames for 30 Minutes

Stronghold contains isopropyl alcohol as its carrier solvent. This makes the wet solution highly flammable. After application, keep the animal away from gas hobs, open fireplaces, candles, and any ignition source for at least 30 minutes or until the application site is completely dry. This is especially important in households with wood-burning stoves or open flames.

2. No Swimming or Bathing for 2 Hours

The product must remain in contact with dry skin for at least 2 hours to complete absorption. After 2 hours, bathing or swimming does not reduce efficacy — selamectin has been absorbed systemically and the topical solvent carrier has evaporated. Do not allow treated animals into rivers, ponds, or streams within 2 hours — selamectin is toxic to aquatic invertebrates at very low concentrations.

3. Apply to Dry Coat Only

The coat must be completely dry at the time of application. Do not bathe the animal before applying, then immediately apply Stronghold. Plan application when the animal has been dry for several hours.

Stronghold vs Frontline vs Advocate: Complete Comparison

The decision framework:

• Stronghold if: you want heartworm prevention + flea control + roundworms in one product; you have a Collie breed where moxidectin risk is a concern; you don’t need tick or lungworm coverage
• Frontline if: tick coverage is the primary need; you want a simple, inexpensive flea-only product
• Advocate if: you’re in a lungworm risk area (urban foxes, slugs/snails in the garden); note that Advocate is used with caution in MDR1-affected breeds

Where to Buy Stronghold

You can order Stronghold (Selamectin) Spot-On – 3 Pipettes for Cats and Dogs from PetShopBoss.com with free worldwide shipping.

Related: Effipro Duo Spot-On (Fipronil + Permethrin) – tick-focused alternative | Advocate (Imidacloprid + Moxidectin) – includes lungworm coverage