Background: Fenitrothion (MEP) is the most frequent cause of organophosphate pesticides (OP) poisoning in Japan, but clinical parameters to predict its severity remain uncertain.
Method: We evaluated 26 cases (12 males and 14 females) of MEP poisoning brought to our critical care center. Regarding acute lung injury (ALI) as a hallmark complication leading to poor recovery, we divided patients into two groups: cases without ALI (Grp1, n = 14), and cases who developed ALI (Grp2, n = 12) at various points after the poisoning. Serial changes in clinical parameters and laboratory test results were compared between them.
Results: The median MEP concentrations on arrival (min~max) for Grp1 and Grp2 were 2.3 (0.5-5.1) and 4.6 (1.1-14.0) μg/ml, respectively. Serum pseudo-cholinesterase (PChE) levels on arrival were 21(< 10-59) U/L in Grp1 and < 10 in Grp2. Based on individual patient kinetics, we estimated MEP concentration at 2 and 24 hours after ingestion, and determined cutoff values for differentiating the two groups for each time point as 4.0 μg/ml and 0.5 μg/ml, respectively. By logistic regression analysis, two groups were distinguished with accuracy of 92.3% based on their time of arrival after ingestion and initial MEP concentration. Clinical parameters associated with ALI were days with miosis, days with PChE below 100 U/L, and days requiring administration of atropine.
Conclusion: The severity of MEP poisoning is closely associated with both time to presentation after ingestion and initial MEP concentration. Serial monitoring of MEP concentrations in the first 24 hours is also useful in predicting the clinical course.