Potential Toxicity of Boric Acid Powder Otic Insufflation

Objective: Boric acid (BA) powder is commonly used to treat otologic conditions, such as mastoid bowl inflammation and chronic otitis externa. Exposure to 50 mg per day is thought to cause systemic toxicity in humans. Inflamed skin and mucosal surfaces readily absorb BA. The aim of this study was to measure the doses of BA commonly used in clinical otology and alert the otolaryngology community to BA's underappreciated potential source of systemic toxicity.

Study design: Prospective, controlled.

Setting: Laboratory.

Methods: BA dose administration was measured by weighing the BA generated by common insufflators: accordion bellows, House-Sheehy insufflator, DeVilbiss insufflator, and pneumatic powder blower. Manual insufflation was performed with 3 compressions of the bulb. The pneumatic blower was sprayed for 1 second. Measurements were repeated 10 times.

Results: The DeVilbiss insufflator delivered the lowest mean BA dose, 6.1 mg (SD 3.4, range 2.1-13.7), followed by the House-Sheehy 8.9 mg (SD 8.4, range 1.6-27.8), the pneumatic blower 192.8 mg (SD 38.3, range 150.0-261.7), and the accordion, 284.1 mg (SD 215.0, range 37.8-730.8).

Conclusion: BA dose delivery is highly variable by insufflator type, and doses thought to cause systemic toxicity are commonly generated. Awareness of and further investigation into the potential toxicity of otic administration of BA seems warranted.