Last Updated: 2008-01-17 19:01:06 -0400 (Reuters Health)

NEW YORK (Reuters Health) – Patients who are resistant to the effects of aspirin are at increased risk for long-term cardiovascular morbidity, according to a report in January 18th Online First issue of the British Medical Journal.

"Studies need to be designed to determine the most useful test to identify aspirin resistance and identify alternative effective therapies for patients who are resistant to aspirin," Dr. Michael R. Buchanan, from McMaster University in Hamilton, Ontario, Canada, and colleagues conclude.

To look at how aspirin resistance affects cardiovascular morbidity, the researchers conducted a systematic review and meta-analysis of 20 relevant studies involving 2930 patients. The aspirin dose used in the studies ranged from 75 to 325 mg/daily and six of the studies included adjunct antiplatelet therapy.

Treatment compliance was directly verified in 14 of the studies and by interviews or telephone in three, the researchers state.

Aspirin resistance was identified in 28% of subjects. Compared with aspirin-sensitive subjects, those with resistance were 3.85-, 5.99-, and 4.06-times more likely to experience a cardiovascular event, death, or an acute coronary syndrome, respectively.

Moreover, there was no evidence that other antiplatelet therapies were beneficial for aspirin-resistant subjects, the report suggests.

In a related editorial, Dr. Giuseppe Biondi-Zoccai, from the University of Turin, Italy, and Dr. Marzia Lotrionte, from Catholic University in Rome, comment that several questions remain: "We don’t know whether aspirin resistance is a true abnormal response or whether it reflects normal variability in drug activity. We also aren’t clear whether aspirin resistance has a negative prognostic effect independent of more traditional risk factors, such as diabetes or obesity."

BMJ 2008.

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