Toxicokinetic Study of Acute Paraquat Poisoning

The rate of mortality from paraquat poisoning is high and the principal manifestation of toxicosis is pulmonary impairment. In this study, we measured the concentration of paraquat in the urine, blood, and some organs in 10 patients with acute paraquat poisoning in order to study the relationships of the kinetics in the body to the concentration in the lungs and to the pulmonary impairment. The concentration of paraquat dichloride in the blood stream rapidly decreased in the first 24 hours. The half life was about 0.5 hour, within 2 hours (case 3) after intoxication, about 1 hour after 5 hours (case 5), about 2 hours after 10 hours (case 6) and after 24 hours (case 6) was prolonged to over 26 hours. Therefore, it was suggested that half life was subsequently prolonged with the passage of time. There were indications that renal disturbance appeared in about 5 hours after oral intake. Accumulations of paraquat were seen in the organs examined. The largest amount within 24 hours after exposure was recognized in the lungs, and the largest amount after 271 hours was seen in the skeletal muscle. The concentration of paraquat in the lungs was higher than the concentration levels in the blood at death in all the cases. Although excretion of paraquat from the lungs was very slow. it became faster with DHP and HD. However, excretion from the skeletal muscle was slow, Excretion from the other organs excepting the kidney was considered to be constant, being proportional to the blood concentration levels. The pathologic examination of the lungs found congestive edema in 6 cases, which became severer with the lapse of time. Partial pulmonary fibrosis was recognized only in long-term survival cases. The cause of irreversible pulmonary impairment was considered to be the effect of the small amount of paraquat remaining in the lungs which exceeds the concentration in the blood.