Human Imazethapyr Poisoning – A First Reported Case

To the Editor, We wish to highlight a rare case of acute imazethapyr poisoning, which, to our knowledge, has not been previously documented in humans. Acute pesticide poisoning remains a major cause of illness and death in India. Imazethapyr, a relatively uncommon herbicide approved initially in the U.S., is marketed under various brand names such as Adama, Super Suit, and Imaza, containing 10% of the active ingredient. While imazapyr, a related compound, is known to cause altered sensorium, respiratory depression, metabolic acidosis, and hypotension, there are no prior reports of human imazethapyr poisoning.[1] We present the first documented case of acute imazethapyr poisoning in a 70-year-old female who ingested approximately 50 ml of Imazethapyr 10% soluble liquid (SL) solution (equivalent to 5 g) following a domestic dispute. She was admitted to a local hospital within 2 h, where gastric lavage was performed. After lavage, she experienced vomiting and one episode of loose stools. She was transferred to our facility on the same day for further management. Upon arrival, she was asymptomatic with stable vital signs except for oxygen saturation at 88% on room air. Auscultation revealed wheezing and crepitus in the right interscapular region. Laboratory investigations showed leukocytosis (15,000/μL) and hyponatremia (131 mEq/L). Her liver and renal function tests were within normal limits. The chest X-ray showed no remarkable findings. Arterial blood gas analysis indicated type 1 respiratory failure. She was treated with bronchodilators and oxygen therapy, which were tapered and discontinued by the 3rd day. Nonpharmacological interventions included chest physiotherapy and supervised incentive spirometry. Antibiotic therapy was deemed unnecessary as the patient did not develop a fever. She was discharged in stable condition on the 4th day and remained well at the 6-month follow-up. Imazethapyr is commonly used in crops like soybeans and rice to control broadleaf weeds. Its toxicity results from inhibiting the synthesis of branched-chain amino acids via acetolactate synthase.[2] Despite its plant-specific mode of action, which indicates low mammalian toxicity, the safety profile of the compound in humans remains undocumented.[3] In our patient, gastrointestinal irritation and probable chemical pneumonitis were observed, possibly caused by gastric lavage. This underscores the need to reevaluate the safety of lavage in such poisonings. Hyponatremia, in the absence of abnormal glucose levels, may also be linked to lavage. The patient’s response to bronchodilators and oxygen therapy was favorable, and she had no prior history of obstructive airway disease or biomass fuel exposure. Animal studies report oral median lethal doses over 5000 mg/kg in mice and over 2000 mg/kg in rats and rabbits.[4] According to the World Health Organization classification, imazethapyr falls under class “U,” which is unlikely to pose an acute hazard.[5] Our patient ingested approximately 5 g; however, she recovered without complications. While imazethapyr is a prototype of the more toxic imazapyr, no genotoxic effects have been observed in humans through dietary exposure. This case suggests low toxicity of imazethapyr in humans, though further research is needed. Chemical pneumonitis should be considered during management, and the absence of an antidote highlights the importance of supportive care. Declaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.