Use of clopidogrel with or without aspirin in patients taking oral anticoagulant therapy and undergoing percutaneous coronary intervention: An open-label, randomised, controlled trial - The Lancet - 2013

Brief Summary:

In patients on oral anticoagulation undergoing PCI, use of clopidogrel alone (double therapy) was associated with a significant reduction in bleeding complications compared to patients receiving clopidogrel with aspirin (triple therapy).

Reference: http://www.ncbi.nlm.nih.gov/pubmed/23415013