PHARMACOKINETIC ASSESSMENT OF THE DERMAL ABSORPTION OF N,N-DIETHYL-M-TOLUAMIDE (DEET) IN CATTLE

Model independent pharmacokinetic methods based on statistical moments were applied to investigate the plasma disposition characteristics of N,N-diethyl-m-toluamide (DEET insect repellent) after single-dose tre atment of experimental cattle by rapid intravenous injection (2.5-2.7 mg/kg) and by dermal application (10 mg/kg) to the back. DEET was dete rmined in jugular blood samples by capillary GC with a nitrogen select ive detector and an internal standard of N,N-dipropyl-m-toluamide. Usi ng weighted least squares linear regression analysis, the assay was va lidated over the concentration range of 19-1910 ng/ml of plasma. Compa rison of areas under the plasma concentration-time curves after intrav enous and dermal treatments of four Hereford heifers indicated that 72 .9 +/- 8.3% (mean +/- SD) of the dermally applied dose was absorbed in to the systemic circulation. The time-to-peak plasma concentrations fo llowing dermal treatments was 37.5 +/- 8.7 min. Apparent elimination r ate constants were not significantly different between the two routes of administration. Linear pharmacokinetics was demonstrated with four additional cattle by comparing systemic clearance after intravenous in fusion to steady-state plasma levels of similar to 0.5 and 2.5 mu g/ml . The rapid and extensive dermal absorption of DEET observed in this s tudy will probably contribute to a short duration of insect repellent action if ethanol based sprays are used to protect cattle under field conditions.