Pharmacokinetics of picloram in male volunteers

The fate of picloram (4-amino-3,5,6-trichloropicolinic acid), an active ingredient in TORDON brand herbicides, was defined in 6 healthy male volunteers following single po doses of 5.0 and 0.5 mg/kg, and a dermal dose of 2.0 mg/kg. Picloram was administered orally as the sodium salt in grape juice. The dermal dose was applied to the volunteers' backs as the free acid dissolved in ethanol. The data indicate picloram was rapidly absorbed from the gastrointestinal tract (t1/2 = 20 min) and rapidly excreted unchanged in the urine. Over 90% of the po dose was recovered as unchanged picloram in the urine excreted through 72 hr; most of the dose (greater than 75%) was excreted within 6 hr and the remainder was excreted with an average half-life of 27 hr. By comparison picloram was slowly absorbed through the skin (t1/2 = 12 hr) and, based on the quantity of picloram excreted in the urine, only a small fraction (0.2%) of the picloram applied to the skin was absorbed. These data indicate that picloram because of its rapid excretion has a low potential to accumulate in man during repeated or prolonged exposures. In addition, picloram was poorly absorbed through human skin and it is unlikely that acutely toxic quantities will be absorbed by this route.