Fate of silvex following oral administration to humans

The fate of silvex [2-(2,4,5-trichlorophenoxy)propionic acid] was defined in seven men and in one woman following oral administration of 1 mg/kg. No adverse effects were observed. Samples of blood plasma, urine, and feces were collected at designated time intervals through 168 hr. Plasma samples were analyzed for silvex only, while samples of urine and feces were analyzed for silvex, silvex conjugate(s), 2,4,5-trichlorophenol, and 2,4,5-trichlorophenol conjugate(s). Apparent first-order kinetics described the biphasic clearance of silvex from plasma and excretion in urine. The half-life values for clearance of silvex from plasma were 4.0 +/- 1.9 and 16.5 +/- 7.3 hr for the initial and terminal phases, respectively. Peak plasma levels of silvex occurred within 2-4 hr after dosage. Within 24 hr after administration, 65% of the administered dose had been excreted in urine. Silvex was excreted in urine as silvex and silvex conjugate(s). The half-life values for excretion of silvex per se in urine were 5.0 +/- 1.8 and 25.9 +/- 6.3 hr for the two phases, respectively. Small amounts (3.2% or less) of silvex and/or silvex conjugate(s) were eliminated in feces. Recovery of silvex and its conjugate(s) in urine and feces through 168 hr ranged from 66.6 to 95.1% of the administered dose, with a mean value and standard deviation of 80.3 +/- 10.5%. In humans, silvex is readily absorbed after ingestion and subsequently readily excreted, predominantly via the urine.