Management of Methemoglobinemia due to Terpene-lactoid Poisoning: A Case Report

In today’s world, herbal or “natural” insecticides are generally considered benign, but their toxic potential remains inadequately recognized. We report the case of a 75-year-old man who voluntarily took a commercially available herbicide containing terpenes, alkaloids, lactones and emulsifiers. He presented himself to the emergency department with repeated vomiting, altered sensors, progressive cyanosis and hypoxia, which did not improve despite additional oxygen. Initial clinical results differed from pulse oximetry measurements, prompting further investigation. Co-oximetric analysis of arterial blood gas revealed severe methemoglobinemia with a level of 56.6% of methaemoglobin, accompanied by significant lactic acidism (lactate 13.1 mmol/L). The patient underwent immediate gastric decontamination, airway protection and intensive support care. After confirmation of normal glucose-6-phosphate dehydrogenase levels, intravenous methyl blue was administered along with ascorbic acid and thiamine. After antidotal therapy, levels of methaemoglobin normalized rapidly, lactate concentrations declined, and the neurological state improved considerably. The patient was successfully liberated from ventilator support and recovered without residual sequelae. This case highlights the often-overlooked toxicity of herbal insecticides and emphasizes the importance of considering methemoglobinemia in patients with unexplained cyanosis and saturation gap, where early recognition and targeted treatment can save lives.