Pseudoresistance and Pseudoprotection: Is It Time to Abandon Enteric-Coated Aspirin?

Many, if not most, patients on daily aspirin therapy have been advised or otherwise chosen to use the enteric-coated variety in the belief that it is safer, regardless of whether they have a history of peptic ulcer disease or aspirin intolerance. Perhaps such recommendation reflects a prevailing view in the primary care community. For years, my own recommendation has been to avoid such practice because of the notion that enteric coating can diminish absorption and overall effectiveness of the drug as an antiplatelet agent – and increase cost. And I may have been on the right track all along.

In a significant study of 400 healthy adults aged 18 years to 55 years, platelet-inhibition response to the administration of a single 325-mg dose of immediate-release or enteric-coated aspirin was evaluated to assess the activity of cyclooxygenase-1. Among several salient findings, these stand out: all of the individuals receiving immediate-release aspirin were responders, but up to 49% of those given enteric-coated aspirin were nonresponders. Furthermore, with repeated exposure, nonresponders turned into responders when given immediate-release aspirin.¹

One of the powerful conclusions of the study is that aspirin resistance may not actually exist. It would appear that enteric coating interferes with intestinal absorption to such an extent as to render the drug ineffective as far as platelet inhibition is concerned. This is consistent with previous thoughts and data, bringing into question the wisdom of using enteric coating. Worse yet, the alleged protection against risk of gastric bleeding provided by these preparations is grounded on shaky or little evidence at best, so there may be no reason to even consider use of enteric coating in most instances.

Thought-provoking and potentially practice-changing as the above take-home messages may be, it is important to note the study used healthy volunteers, so these results will need to be replicated by others and shown to be applicable to the atherosclerotic patient population. That said, the study’s outcome is nothing short of an eye-opener that could have major impact on millions taking aspirin every day when and if enteric coating can be confirmed to be the culprit that causes pseudo-resistance to the drug through absorption interference, and without providing proven protection against gastric side effects. The day may come when marketing-driven pressures become insufficient to perpetuate a bad practice. 

Reference

1. Grosser T, Fries S, Lawson JA, Kapoor SC, Grant GR, Fitzgerald GA. Drug resistance and pseudoresistance: An unintended consequence of enteric coating aspirin. Circulation. 2013;127(3):377-385.