There has been much written in the press about a potential dangerous interaction between Plavix and a commonly used class of antacids called proton pump inhibitors. This class of medications includes drugs like: omeprazole (Prilosec), esomeprazole (Nexium), pantoprazole (Protonix) ...
It is true that testing of platelets in a test tube have show that using PPI's can decrease the potency of Plavix (potentially leading to more MIs), this has not been in many observational studies. Strangely and in a surprise to most Cardiologists, the FDA forced the makers of Plavix to warn their patients about this test tube interaction.
This potential interaction has only been tested in one randomized clinical trial. The COGENT randomized almost 4,000 patients and found NO increased signal for increased cardiovascular events. What it did show was a highly statistically significant decrease in gastrointestinal events (GI bleeding and ulcers) in the patients taking both omeprazole and Plavix.
I have been using Plavix in conjunction with PPI's for years. I have never seen an increase in MI's or other cardiovascular events in these patients. The COGENT trial supports what I have seen clinically -- while there may be an interaction in the test tube, the concomitant use of Plavix and a PPI is not only safe but also possible helpful.