They state that the concomitant use of these drugs should be avoided unless absolutely necessary as clopidogrel may be less effective in patients receiving clopidogrel and a PPI.
Clopidogrel is a pro-drug that is metabolised by cytochrome P450 2C19 to its active form. PPIs may inhibit this isoenzyme and therefore interfere with the antiplatelet activity of clopidogrel.
The manufacturers are conducting further studies to characterise the potential effects of PPIs and CYP2C19 genetic factors on the activity of the drug. In the meantime, patients should continue to take clopidogrel as directed.
Advice to healthcare professionals from the MHRA remains the same. All patients currently receiving clopidogrel and PPIs should be reviewed at their next appointment; concomitant use of these medicines should be avoided. PPIs should only be prescribed within their licensed indications where possible and prescribers should check that patients prescribed clopidogrel are not taking over-the-counter omeprazole.
Further information: Sanofi-aventis