Oral and Dermal Pharmacokinetics of Triclopyr in Human Volunteers

Blood levels and urinary excretion of triclopyr, the active ingredient in Garlon herbicides, were followed in six volunteers given single oral doses of 0.1 and 0.5 mg/kg body weight. Five of these volunteers later received dermal applications of Garlon 4 herbicide formulation equivalent to 3.7 mg triclopyr/kg body weight applied to the forearm. Following oral administration blood levels peaked at 2-3 h and declined to undetectable levels within 48 h; more than 80% of the dose was found as unchanged triclopyr in the urine. A two-compartment pharmacokinetic model was used to describe the time-course of triclopyr clearance; half-lives for the rapid initial and slower terminal phases were 1.3 h and 5.1 h respectively, and were independent of dose. Due to the slow half-life for dermal absorption (t1/2 = 16.8 h) the rapid initial elimination phase was obscured and the pharmacokinetics could be simplified by a one-compartment model. An average of 1.37% of the applied dose was recovered in the urine; when corrected for recovery after oral administration this was equivalent to an absorption of 1.65%. Triclopyr is slowly absorbed through skin and is rapidly eliminated. It has very low potential to accumulate in man or to be absorbed through the skin in acutely toxic amounts.