Urine Methyl Hippuric Acid Levels in Acute Pesticide Poisoning: Estimation of Ingested Xylene Volume and Association with Clinical Outcome Parameters

To determine the relationship between the oral ingestion volume of xylene and methyl hippuric acid (MHA) in urine, we measured MHA in 11 patients whose ingested xylene volume was identified. The best-fit equation between urine MHA and ingested amount of xylene was as follows: y (ingested amount of xylene, mL/kg) = -0.052x² + 0.756x (x = MHA in urine in g/g creatinine). From this equation, we estimated the ingested xylene volume in 194 patients who had ingested pesticide of which the formulation was not available. Our results demonstrated that oxadiazole, dinitroaniline, chloroacetamide, organophosphate, and pyrethroid were xylene-containing pesticide classes, while the paraquat, glyphosate, glufosinate, synthetic auxin, fungicide, neonicotinoid, and carbamate classes were xylene-free pesticides. Sub-group univariate analysis showed a significant association between MHA levels in urine and ventilator necessity in the pyrethroid group. However, this association was not observed in the organophosphate group. Our results suggest that MHA in urine is a surrogate marker for xylene ingestion, and high urine MHA levels may be a risk factor for poor clinical outcome with some pesticide poisoning.