Stronghold For Dogs 40.1-85 lbs (20.1-40 kg)

Description

Stronghold for Dogs 40.1–85 lbs (20.1–40.0 kg) contains 240 mg selamectin per 2.0 ml tube, produced by Zoetis as a topical spot-on solution covering large-breed dogs in this weight category. Selamectin is an avermectin-class macrocyclic lactone that interferes with chloride channel conductance in invertebrate nerve and muscle cells, generating paralysis and death across a range of external and internal parasites through systemic distribution following transdermal absorption. This variant is approved for dogs from 6 weeks of age weighing between 20.1 and 40.0 kg, with monthly application for flea and heartworm larval prevention alongside single-dose or two-dose treatment protocols for ear mites, roundworms, biting lice, and sarcoptic mange.

Recommended for

Dogs weighing 40.1–85 lbs (20.1–40.0 kg) from 6 weeks of age.

Indication/Coverage

For dogs suffering from, or at risk from, mixed parasitic infections, Stronghold 240 mg addresses the following conditions:

• Flea treatment and prevention (Ctenocephalides spp.): Selamectin kills adult fleas on the dog, prevents viable egg production, and destroys environmental larvae; ovicidal activity persists for 3 weeks post-application, breaking the flea reproductive cycle at every stage present on the animal and in surrounding areas.
• Heartworm prevention (Dirofilaria immitis, L3/L4 larvae): Monthly dosing eliminates susceptible larval stages acquired during the preceding interval; the product has no activity against adult heartworms already established in the pulmonary vasculature.
• Ear mite treatment (Otodectes cynotis, adults): A single dose constitutes the full labeled treatment course; loose debris from the external ear canal should be gently cleared at the time of treatment, and a veterinary follow-up examination at 30 days is recommended as some dogs require a second application.
• Roundworm treatment (Toxocara canis, adults): A single dose clears adult intestinal roundworm burden from the gastrointestinal tract.
• Sarcoptic mange treatment (Sarcoptes scabiei): Complete mite elimination requires one dose administered on each of two consecutive months; compressing both doses into a shorter interval does not satisfy the labeled protocol.
• Biting lice treatment (Trichodectes canis): A single topical application eliminates biting lice infestations in dogs within this weight range.

Key Benefits

The following properties are confirmed by the Stronghold label for the 240 mg dose covering dogs in the 20.1–40.0 kg range.

• Large-breed dose calibration: The 240 mg selamectin dose maintains a minimum of 6 mg/kg across the full 20.1–40.0 kg range, keeping the per-kilogram concentration within the labeled therapeutic window at both weight boundaries.
• Six-indication coverage: Fleas, heartworm larvae, ear mites, roundworms, sarcoptic mange, and biting lice are all addressed through a single monthly tube, reducing the number of separate parasiticide products required for large-breed dogs.
• Environmental flea suppression: Debris shed by a selamectin-treated dog destroys flea eggs and larvae in the surrounding environment that have not been directly exposed to the compound, extending population-level flea control beyond the animal itself.
• Oral-free internal coverage: Selamectin is absorbed transdermally following neck application and reaches maximum plasma concentration within approximately 3 days in dogs, providing heartworm larval and intestinal roundworm coverage without requiring the dog to accept an oral dose.
• Sustained monthly plasma levels: The terminal elimination half-life of selamectin in dogs is approximately 11 days, maintaining detectable plasma concentrations throughout the full 30-day dosing interval and underpinning consistent flea and heartworm larval protection.
• Bathing tolerance from 2 hours post-application: The Stronghold label confirms that bathing or immersion 2 or more hours after application does not reduce product efficacy, an important practical consideration for large-breed dogs that swim or undergo regular professional grooming.
• Confirmed safety in breeding animals: Zoetis administered Stronghold at 3 times the recommended dose to pregnant and lactating females without adverse effects, supporting use in breeding large-breed females within this weight category.
• Broad safety margin across breeds: Zoetis safety data confirm no adverse effects at 10 times the recommended dose; field testing covered over 100 pure and mixed dog breeds, with ivermectin-sensitive collies tested separately at 5 times the recommended dose with no adverse effects observed.

Caution

Hazards to Humans

This product is highly flammable; keep it away from heat, open flame, and sparks throughout handling. Do not smoke, eat, or drink during application. Wash hands thoroughly with soap and water immediately after use. Flush any skin or eye contact with water at once and seek medical attention for eye exposure. Keep children away from treated dogs for at least 30 minutes or until the coat is fully dry.

Hazards to Domestic Animals

Stronghold 240 mg is for external use in dogs only; do not administer orally or by injection. This variant is not for use in dogs under 6 weeks of age, and the labeled dose covers animals up to 40.0 kg only. Do not apply when the coat is wet. Dogs that are debilitated or in poor body condition for their age and size should not receive this product without prior veterinary assessment. Reversible neurological signs including seizures have been reported on rare occasions with macrocyclic lactone-class products; veterinary clearance should be obtained before use in any dog with a known history of neurological sensitivity. No interactions with routinely used veterinary medications or surgical procedures were identified in extensive field trials.

Possible Side Effects:

Monitor your dog after each application, with particular attention to the first dose.

Dermal reactions at the application site are uncommon. Temporary hair clumping or a trace amount of white powder may appear at the treated area within the first 24 hours; this is a documented characteristic of the drying solution, resolves without intervention, and does not indicate any compromise to product safety or efficacy.

Systemic reactions are exceptional but documented. Selamectin, as a macrocyclic lactone, carries a low risk of reversible neurological signs including seizures; this has been recorded only rarely across extensive field and safety testing. Ivermectin-sensitive collie breeds were studied at 5 times the recommended dose without adverse neurological findings, though individual sensitivity in any given dog cannot be entirely excluded.

If persistent skin changes, behavioral abnormalities, or unexpected systemic signs develop following dosing, discontinue use and contact a veterinarian without delay.