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Naproxen Does Not Affect Cardiovascular Benefits of Aspirin: Presented at ACR

By Bruce Sylvester

BOSTON, MA -- November 12, 2007 -- Unlike ibuprofen, naproxen does not interfere with the potentially life-saving antiplatelet effects of aspirin therapy, researchers reported here at the 71st annual meeting of the American College of Rheumatology (ACR).

"We have been faced with a problem, as rheumatologists, when patients are using aspirin but need more pain relief, and ibuprofen carries a label warning [against coadministration with aspirin]," said presenter Michael Schiff, MD, Director of Clinical Research, Denver Arthritis Clinic, Denver, Colorado.

Dr. Schiff and colleagues conducted their study to evaluate the inhibition of serum thromboxane B₂ (TXB₂) as an indicator of platelet inhibition in subjects taking low-dose enteric-coated aspirin when an over-the-counter dose of naproxen sodium or acetaminophen was added to treatment.

The study was a single-center, randomized, open-label, 3-period trial in healthy subjects. During period 1 (days 1-5), all subjects received aspirin 81 mg once daily for 5 days. In period 2 (days 6-10), subjects were randomized to 5 days of one of the following regimens: aspirin 81 mg once daily; aspirin 81 mg once daily plus acetaminophen 1000 mg four times daily; or aspirin 81 mg once daily plus naproxen 220 mg three times daily.

During an exploratory evaluation (period 3, day 11-12), subjects in the naproxen group received 2 days of therapy with only aspirin 81 mg once daily.

The primary endpoint was inhibition of serum thromboxane B₂ (TXB₂) on day 11. The investigators defined inhibition as clinically relevant if the noninferiority test of the one-sided 95% confidence interval (CI) remained greater than 90%.

The investigators used acetaminophen as a comparator because previous research has shown that it does not affect the antiplatelet effects of aspirin.

The researchers randomized 47 subjects, 45 of whom met the criteria for the intent-to-treat population. A total of 37 subjects (12 naproxen + aspirin; 13 acetaminophen + aspirin; 12 aspirin only) met the criteria for the evaluable population, which the investigators defined as subjects with no protocol violations and whose TXB₂ inhibition levels were at least 95% after 5 days of aspirin therapy.

The combination of aspirin and acetaminophen or aspirin and naproxen for 5 days following 5 days of aspirin monotherapy maintained high levels of TXB₂ inhibition (>99%), the researchers reported.

In the intent-to-treat population, mean TXB₂ inhibition during period 2 was also >99%, supporting the results observed among evaluable subjects. Also, in the exploratory analysis of subjects who discontinued naproxen but continued with aspirin for 2 days, the majority of subjects (n = 9) achieved serum TXB₂ levels of at least 95%.

"In this study we have found that naproxen does not appear to interfere with aspirin's antiplatelet effects," Dr. Schiff concluded.

"These findings are good news for the many people who use low-dose aspirin [for cardiovascular protection] but also need more over-the-counter treatment for pain, including the minor pain of arthritis. Naproxen appears to be a safe option." Dr. Schiff added.

Funding for this study was provided by Bayer HealthCare.


[Presentation title: The Platelet Inhibitory Effects of the Combination of Naproxen Sodium or Acetaminophen With Low Dose Aspirin. Poster 90]

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