Friday, July 20, 2018

Low Dose Aspirin May Not Be Effective in Heavier Patients

Low-dose aspirin may not be effective in preventing cardiovascular events in people weight 70 kg (154 pounds) or more, a Lancet study suggests.

Researchers analyzed 10 trials that evaluated aspirin versus controls for primary prevention of cardiovascular events in 120,000 people.

Daily, low-dose aspirin (75-100 mg) was associated with reduced risk for cardiovascular events among those weighting less than 70 kg (odds ratio, 0.77), but there was no significant effect for heavier patients – roughly 80% of men in the study and nearly half of women weighted 70 kg or more. In the heavier group, low-dose aspirin may be even less effective in smokers and in those who take enteric-coated aspirin.

High-dose aspirin (300-325 or 500 mg), meanwhile, appeared to be effective in reducing primary cardiovascular events only [in] patients weight 70 kg or more.

Commentators said that people with more body mass may have more esterases, which clear aspirin and would reduce the bioavailability of the drug.

The authors conclude: “A one-dose-fits-all approach to aspirin is unlikely to be optimal, and a more tailored strategy is required.

My Take:
The use of aspirin, at any dose, for primary prevention of cardiovascular events is not a standard of practice. That is because several studies have shown that the side effects from daily aspirin far outweigh any possible preventive benefits. However, once you have had a CVE the risk factors rise high enough to outweigh the known side effects – GI bleed, liver failure and death.

Despite all the studies, many primary care physicians continue to recommend a low-dose aspirin as primary prevention for their patients. They also frequently recommend aspirin in combination with other blood thinners, like Plavix, also a contraindication.

Now this new study indicates that low-dose aspirin isn’t even effective for most people (those over 154 pounds).

Aspirin was first produced by the Bayer Company in 1904. It was loosely based on the herb White Willow Bark. The active ingredient in White Willow Bark was thought to be salicylic acid. So, Bayer took citric acid and combined it with acetone and made acetylsalicylic acid (aspirin).

It wasn’t unto 1994 when the chemical pathways for Cox inhibitors, like Advil and Motrin were unraveled that the true chemical nature of aspirin was uncovered. It turns out that the active ingredient in aspirin is the acetone, a Cox inhibitor. That’s right, the anti-inflammatory and blood thinning actions of aspirin are from nail polish remover.

Researchers have gone back to look at White Willow Bark, isolating 75 different chemical compounds, none of which seem to account for its anti-inflammatory action. Although White Willow Bark is effective, I seldom recommend it as we don’t know its mode of action.

Bottom Line:
Please don’t take aspirin, at any dose, for primary prevention. However, if you have had a cardiac event then consult with your cardiologist about aspirin use, dosage and possible contraindications with any other drugs you are taking.

Source: July 16, 2018 New England Journal of Medicine

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