Plasma salicylate from methyl salicylate cream compared to oil of Wintergreen

Background. Poison Control Centers follow the acetylsalicylic acid (ASA) treatment guideline to manage unintentional ingestions of topical methyl salicylate liniments. For example, one teaspoon of 30% methyl salicylate cream such as Ben Gay® provides an "ASA equivalent dose" of 180 mg/kg for a 10 kg child. The ASA treatment guideline advises emesis with syrup of Ipecac and 24 h home followup for this dose. Both the ASA conversion factor to yield the ASA equivalent dose and the treatment guideline assume 100% bioavailability of the salicylate. The nature of this topical dosage product led the investigators to expect less than complete absorption of methyl salicylate. Objective. To compare plasma concentrations of salicylate from ingested methyl salicylate cream with plasma concentrations of salicylate from ingested oil of wintergreen. Methods. Four adult volunteers consented to an open label, four-way crossover design, with randomization to the following treatments: 1 mL Oil of Wintergreen, U.S.P., 6.7 g of Ben Gay® 15% and 20 g of Ben Gay® 15% and also to hold 5 g of Ben Gay® 15% cream in the buccal cavity for 1 minute and then expectorate. Plasma was collected for salicylate determination, and the results analyzed with a noncompartmental pharmacokinetic model. Results. No plasma salicylate was detected after buccal treatment phase. Relative bioavailability for the low-dose treatment was 0.5 compared to oil of wintergreen. Conclusion. Plasma salicylate concentrations from methyl salicylate cream are not equal to those achieved after ingestion of oil of wintergreen. Dosage formulation must be considered when predicting toxicity.