How do flea drops applied to a dog's neck work? - briefly
The spot‑on solution penetrates the skin at the neck, enters the bloodstream, and spreads to the skin and hair follicles where it kills or repels fleas. Its active compounds persist in the dog’s lipid layers, providing protection for several weeks.
How do flea drops applied to a dog's neck work? - in detail
Flea spot‑on products are liquid formulations placed on the shaved area at the back of a dog’s neck. The liquid spreads across the skin surface, penetrates the epidermis, and enters the bloodstream. Once in the circulatory system, the active molecules travel to the skin and hair follicles where adult fleas, larvae, and eggs are encountered.
The active ingredients belong to several chemical classes:
- Neonicotinoids (e.g., imidacloprid, dinotefuran): bind to nicotinic acetylcholine receptors in the insect nervous system, causing paralysis and death.
- Phenylpyrazoles (e.g., fipronil): block GABA‑gated chloride channels, disrupting neuronal inhibition and leading to hyperexcitation.
- Macrocyclic lactones (e.g., selamectin): interfere with glutamate‑gated chloride channels, affecting muscle function in parasites.
- Insect growth regulators (e.g., pyriproxyfen, methoprene): mimic juvenile hormone, preventing maturation of flea eggs and larvae.
After application, the product forms a thin oily film that distributes through natural oil flow across the coat. This film maintains a lethal concentration on the skin for the labeled period, typically 30 days. Fleas contacting the treated surface ingest or absorb the chemical, which acts quickly—usually within minutes—to immobilize and kill the parasite. Eggs laid on the dog are exposed to the growth regulator, halting development and breaking the life cycle.
Pharmacokinetic profile:
- Absorption: rapid dermal uptake within hours.
- Distribution: systemic spread via plasma; concentration peaks in skin and hair follicles.
- Metabolism: minimal hepatic metabolism; most compounds remain unchanged to retain efficacy.
- Elimination: slow release from the skin surface; residues persist at therapeutic levels for the product’s duration.
Proper use requires a single dose based on the dog’s weight, applied directly onto the dry skin at the nape. The dog should not be bathed or swim for at least 24 hours to allow complete absorption. Over‑application can lead to toxicity; symptoms include excessive drooling, tremors, or seizures, and warrant immediate veterinary attention.
Resistance management involves rotating products with different active ingredients and integrating environmental control measures such as vacuuming and washing bedding. This strategy reduces selection pressure on flea populations and sustains long‑term efficacy.