Pharmacokinetics of metaflumizone and amitraz in the plasma and hair of dogs following topical application.

Controlled laboratory studies have shown that a metaflumizone plus amitraz combination (ProMeris/ProMeris Duo for Dogs, Fort Dodge Animal Health, Overland Park, KS) applied topically is effective for the treatment and control of fleas and ticks on dogs. Two studies were conducted to determine the distribution of both metaflumizone and amitraz in the plasma and hair of dogs following treatment at the minimum recommended dose of approximately 20mg/kg of each active ingredient. Six purpose-bred, adult Beagle dogs were used in each study. Plasma or hair samples were collected from each dog just prior to dosing and periodically through 56 days after treatment. Samples were analyzed by HPLC methods validated for the simultaneous determination of metaflumizone and amitraz. Amitraz was detectable (>3.2ng/ml) but not quantifiable (<50ng/ml) in only two plasma samples, collected 1 and 2 days post-treatment from different dogs. Metaflumizone concentrations in plasma were generally detectable (>1.0ng/ml) but not quantifiable (<50ng/ml). Measurable levels were found in one dog 7 days post-treatment, increasing to a maximum of four dogs at 42 days after dosing, with a metaflumizone range of 59-138ng/ml. Analysis of hair samples indicated that both metaflumizone and amitraz were widely distributed at basically similar levels in the hair within 1-day after administration, reaching maximum concentrations between 2 and 7 days post-treatment. Low but quantifiable levels of both compounds were still present on hair at the end of the 56-day study. These studies indicate that the ectoparasitic activity is due to exposure of the parasites to metaflumizone and amitraz on the surface of the host (hair and/or skin), not to exposure via the circulatory system of the host.