Pharmacokinetics of metaflumizone in the plasma and hair of cats following topical application

Controlled laboratory studies have shown that a novel spot-on formulation containing 20% (w/v) metaflumizone (ProMeris® for Cats, Fort Dodge Animal Health, Overland Park, KS) is effective for the treatment and control of fleas on cats. Two studies were conducted to determine the distribution of metaflumizone in the plasma and hair of cats following treatment at the minimum recommended dose of 40 mg/kg. Six purpose-bred cats, three males and three females, were used in each study. Plasma or hair samples were collected from each cat just prior to dosing and periodically through 56 days after treatment. Samples were analyzed by HPLC methods validated for the determination of metaflumizone. Metaflumizone concentrations in plasma were below the method limit of quantification (<50 ng/ml) in all samples but one, and were frequently not detectable (<1.1 ng/ml). Plasma collected 3 days post-treatment from one cat had a metaflumizone concentration of 57.8 ng/ml. The frequency of measurable levels of metaflumizone in the plasma was too low to allow the calculation of pharmacokinetic parameters. Analysis of hair samples indicated that metaflumizone was widely distributed in the hair coat of the cat within 1 day after administration, reaching maximum concentrations within 1 or 2 days post-treatment. Low but quantifiable levels were still present at the end of the 56-day study. Data from the present studies indicate that the ectoparasitic activity is due to exposure of the parasites to metaflumizone on the surface of the host (skin and hair), not to exposure via the circulatory system of the host.