Use of Ferric Chloride to Identify Salicylate-Containing Poisons

Abstract

Objective: Ferric chloride (FeCl₃) is used to qualitatively test the urine of patients with presumed salicylate exposure. FeCl₃ testing of an unidentified poison might provide evidence of salicylate exposure in situations where FeCl₃ urine testing cannot be used. Such situations include the absence of a urine sample, immediately after ingestion before urine contains a detectable quantity of salicylate, or for patients chronically using salicylates for which FeCl₃ testing is unhelpful. This study seeks to determine if FeCl₃ can be used to identify salicylate-containing products. Methods: We assessed the reactivity of FeCl₃ with commercially available salicylate-containing products. We applied 0.1 mL of 10% FeCl₃ solution to each of 15 various salicylate-containing products including: regular and buffered acetylsalicylic acid, bismuth subsalicylate, methylsalicylate, physostigmine salicylate, salicylic acid, trolamine salicylate, and herbal tablets with salicin-containing white willow bark (Salix sp.). These products tested were: regular and enteric-coated pills (n=4), powder (n=1), topical creams (n=5), topical liquids (n=4), and intravenous solution (n=1). FeCl₃ was applied to crushed tablets and added directly to liquids and creams. Fifteen salicylate-free controls including liquids, pills, and creams similar in appearance to experimental samples were also tested. Three blinded physicians familiar with FeCl₃ testing independently observed the addition of FeCl₃ to each sample and rated a positive or negative result. Results: All salicylate-containing products were interpreted to be clearly FeCl₃ positive and all control samples were interpreted to be clearly FeCl₃ negative. Conclusion: Salicylate-containing products may be identified using FeCl₃. When using FeCl₃ testing as described herein, only a positive test result should be applied; any negative result should be considered inconclusive.

Keywords :

• Ferric chloride
• Salicylate
• Methylsalicylate
• Poisoning
• Trinder's
• Laboratory
• Assay