Does modulation of organic cation transporters improve pralidoxime activity in an animal model of organophosphate poisoning?

Objectives: Pralidoxime is an organic cation used as an antidote in addition to atropine to treat organophosphate poisoning. Pralidoxime is rapidly eliminated by the renal route and thus has limited action. The objectives of this work were as follows. 1) Study the role of organic cation transporters in the renal secretion of pralidoxime using organic cation transporter substrates (tetraethylammonium) and knockout mice (Oct1/2(-/-); Oct3(-/-)). 2) Assess whether sustained high plasma concentrations increase pralidoxime antidotal activity toward paraoxon-induced respiratory toxicity. Setting: INSERM U705, Faculte de Pharmacie, Universite Paris Descartes, 4 Avenue de l'Observatoire, 75006 Paris, France. Subjects: Rodents: Knockout mice (Oct1/2(-/-); Oct3(-/-)) and Sprague-Dawley rats. Interventions: None. Measurements and Main Results: In rats, the renal clearance of pralidoxime was 3.6-fold higher than the creatinine clearance. Pretreatment with tetraethylammonium (75 mg/kg) in rats or deficiencies in organic cation transporters 1 and 2 in mice (Oct1/2(-/-)) resulted in a significant increase in plasma pralidoxime concentrations. Lack of Oct3 did not alter plasma pralidoxime concentrations. The antidotal activity of pralidoxime (50 mg/kg intramuscularly) was longer and with greater effect, resulting in a return to normal values when administered to rats pretreated with tetraethylammonium. Conclusions: Pralidoxime is secreted in rats and mice by renal Oct1 and/or Oct2 but not by Oct3. Modulation of organic cation transporter activity increased the plasma pralidoxime concentrations and the antidotal effect of pralidoxime with sustained return within the normal range of respiratory variables in paraoxon-poisoned rats. These results suggest a promising approach in an animal model toward the increase in efficiency of pralidoxime. However, further studies are needed before these results are extended to human poisoning. (Crit Care Med 2011; 39: 803-811)