Pharmacokinetic profile and anticholinesterase properties of phenamiphos in male rats.

The pharmacokinetics and anticholinesterase properties of a single oral dose 6 mg/Kg of technical phenamiphos [ethyl 4-(methylthio)-m-tolyl isopropylphosphoramidate] were investigated in male rats. Animals were killed at each time intervals of 0.5, 1.0, 1.5, 3, 6, 12, 24, 48, and 72 hrs after dosing. The total recovered amount of phenamiphos from brain and plasma tissues reached high level at the first time interval and disappeared biexponentially from both tissues to low level at the end of the experiment. Brain tissue has a greater affinity to phenamiphos than plasma tissue. The half-life of the elimination of phenamiphos from brain and plasma were 100 and 212 hr corresponding to the rate constant values of 0.01 and 0.003 hr-1, respectively. Plasma AUC (area under the curve) value was 1239.81 micrograms hr/L, explaining there was no tendency for the compound to accumulate in the brain tissue (AUC = 774.38 micrograms hr/Kg) compared to the plasma. On the other hand, determination of cholinesterase activity showed that, phenamiphos inhibited the enzymes in both brain and plasma, where the depression of ChE activity was usually more marked in plasma than in brain.