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CARDIOLOGY

Comparison of Oral Aspirin Versus Topical Applied Methyl Salicylate for Platelet Inhibition

Medical Toxicologist, Department of Emergency Medicine, Naval Medical Center San Diego, San Diego, CA

D Christopher Danish, DO

Emergency Physician, Department of Emergency Medicine, Naval Medical Center San Diego

Jacqueline M Reardon, DO

Emergency Physician, Department of Emergency Medicine, Naval Medical Center San Diego

Christopher B Chisholm, MD

Emergency Physician, Department of Emergency Medicine, Naval Medical Center San Diego

Michael J Matteucci, MD

Medical Toxicologist, Department of Emergency Medicine, Naval Medical Center San Diego

Robert H Riffenburgh, PhD

Biostatistician, Department of Clinical Investigation, Naval Medical Center San Diego

Reprints: Dr. Tanen, Department of Emergency Medicine, Naval Medical Center, 34800 Bob Wilson Dr., San Diego, CA 92134, fax 619/532-5307, david.tanen{at}med.navy.mil

BACKGROUND: Oral acetylsalicylic acid (aspirin) is the primary antiplatelet therapy in the treatment of acute myocardial infarction and acute coronary syndrome. Methyl salicylate (MS; oil of wintergreen) is compounded into many over-the-counter antiinflammatory muscle preparations and has been shown to inhibit platelet aggregation locally and to be absorbed systemically.

OBJECTIVE: To assess the ability of topically applied MS to inhibit systemic platelet aggregation for patients who are unable to tolerate oral drug therapy.

METHODS: A randomized, prospective, blinded, crossover study was conducted in 9 healthy men, aged 30–46 years. All subjects ingested 162 mg of aspirin or applied 5 g of 30% MS preparation to their anterior thighs. There was a minimum 2-week washout period between study arms. Blood and urine were collected at baseline and at 6 hours. An aggregometer measured platelet aggregation over time against 5 standard concentrations of epinephrine, and a mean area under the curve (AUC) was calculated. Urinary metabolites of thromboxane B₂ were measured by a standard enzyme immunoassay. Differences in and between groups at baseline and 6 hours were tested by the Wilcoxon signed-rank test.

RESULTS: Baseline platelet aggregation did not differ significantly between the 2 arms of the study (median AUC [% aggregation^*min]; binominal confidence intervals): aspirin 183; 139 to 292 versus MS 197; 118 to 445 (p = 0.51). Both aspirin and MS produced statistically significant platelet inhibition; aspirin decreased the AUC from 183; 139 to 292 to 85; 48 to 128 (p = 0.008) and MS decreased the AUC from 197; 118 to 445 to 112; 88 to 306 (p = 0.011). No significant difference was detected between baseline and 6-hour thromboxane levels for either aspirin (p = 0.779) or MS (p = 0.327).

CONCLUSIONS: Topical MS and oral aspirin both significantly decrease platelet aggregation in healthy human volunteers.

Key Words: aspirin, methyl salicylate, platelets, thromboxane

Published Online, August 12, 2008. www.theannals.com, DOI 10.1345/aph.1L128