A volunteer study on the blood salicylate level of excessive use of topical methylsalicylate

Abstract

Objective: The purpose of this study was to evaluate the serum level of salicylate after topical application of methylsalicylate (analgesic balm), and to determine the safety of its use in our population. Methods: This was a human volunteer study involving six volunteers. Each of them applied 10 grams of analgesic balm (containing 5 grams of methylsalicylate) on the limbs, and serial serum salicylate levels were measured just before the trial, and 1, 2, 4 and 8 hours after application. The time required to reach the maximum blood level after application was recorded. Results: The serum salicylate level ranged from non-detectable level up to near therapeutic level in different subjects. The maximum salicylate level measured was 130 mg/L in one of the volunteers 8 hours after application. The calculated systemic bioavailability of dermal methylsalicylate in our study was 19-45%, which was comparable to previous studies. Conclusions: Dermal application of massive amount of analgesic balm may cause unpredictable absorption of methylsalicylate. Patients and physicians should be aware of its potential risk.