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.