How do drops for fleas and ticks work in dogs? - briefly
Spot‑on flea and tick treatments are applied to the skin, where the active ingredient spreads across the coat, penetrates the hair follicles, and enters the bloodstream to kill parasites that bite the dog. The formulation includes a carrier that ensures even distribution and provides protection for several weeks.
How do drops for fleas and ticks work in dogs? - in detail
Topical spot‑on products are applied directly to a thin area of shaved or clipped skin, usually between the shoulder blades. The formulation contains a lipophilic carrier that spreads across the skin surface by capillary action and by the dog's natural grooming. Within minutes the active ingredient penetrates the stratum corneum, reaches the underlying sebaceous glands and enters the systemic circulation. Once in the bloodstream, the compound is distributed through the dermal tissue and reaches the peripheral nervous system of fleas, ticks and other ectoparasites that bite the host.
The insecticidal or acaricidal effect depends on the chemical class:
- Phenylpyrazoles (e.g., fipronil) – block γ‑aminobutyric acid‑gated chloride channels, causing uncontrolled neuronal firing and rapid paralysis.
- Neonicotinoids (e.g., imidacloprid) – bind nicotinic acetylcholine receptors, leading to overstimulation of the nervous system and death.
- Macrocyclic lactones (e.g., selamectin, milbemycin) – enhance chloride influx through glutamate‑gated channels, resulting in paralysis of parasites.
- Isoxazolines (e.g., fluralaner, afoxolaner) – inhibit ligand‑gated chloride channels specific to arthropods, providing long‑lasting kill.
Key pharmacokinetic features:
- Absorption – the oil‑based matrix facilitates rapid transdermal uptake; plasma concentrations peak within 4–6 hours.
- Distribution – lipophilicity ensures widespread deposition in skin and fatty tissue, creating a reservoir that protects against new infestations.
- Metabolism and excretion – hepatic enzymes metabolize the active, and metabolites are eliminated primarily via urine and feces; systemic exposure remains low, minimizing toxicity to the dog.
- Residual activity – depending on the active, protective levels persist from 30 days (fipronil) to 12 weeks (isoxazoline), maintaining efficacy against newly attached parasites.
Efficacy factors:
- Correct dosing based on body weight prevents under‑ or overdosing.
- Application to a clean, dry area maximizes absorption.
- Re‑application follows the product’s labeled interval; missed doses reduce protective coverage.
- Resistance development is mitigated by rotating actives with different modes of action when possible.
Safety considerations:
- Avoid contact with eyes, mucous membranes and open wounds.
- Do not apply to puppies below the minimum weight specified on the label.
- Monitor for adverse reactions such as localized skin irritation or, rarely, neurological signs; discontinue use and consult a veterinarian if they occur.
In summary, spot‑on flea and tick treatments function through rapid transdermal absorption, systemic distribution, and targeted interference with parasite neurophysiology, providing sustained protection when applied according to label guidelines.