Many patients with acute coronary syndrome receive chronic dual antiplatelet therapy (acetylsalicylic acid and clopidogrel) for secondary event prophylaxis, and new oral anticoagulants are being investigated as adjunctive therapy in this indication. Gastrointestinal side effects such as bleeding are commonly associated with antiplatelet use; accordingly, many patients receive proton pump inhibitors (PPIs) to mitigate this. PPIs can reduce the antiplatelet activity of clopidogrel through cytochrome P450 2C19 inhibition, and pantoprazole reduces the bioavailability of dabigatran, a direct thrombin inhibitor that acts via cytochrome P450 2C19-independent mechanisms. These observations support the investigation of potential pharmacokinetic and pharmacodynamic interactions between PPIs and anticoagulants. We evaluated the influence of administering once-daily omeprazole 40 mg for 5 days on the pharmacokinetics and pharmacodynamics of a single 20-mg dose of the oral direct factor Xa inhibitor, rivaroxaban, in a randomized, open-label, 2-way, crossover, drug-drug interaction study in healthy subjects. No clinically meaningful interactions were observed; geometric mean ratios were 101%, 101%, and 93.5% for rivaroxaban area under the plasma concentration-time curve from time 0 to the time of the last quantifiable concentration (AUClast), or until infinity (AUC∞), and maximum plasma concentration (Cmax), respectively. Prothrombin time increased similarly in both treatment groups, with maximal values observed approximately 4 hours post rivaroxaban administration. A single 20-mg rivaroxaban dose appears well tolerated when administered alone or after 5 days of once-daily omeprazole 40 mg administration.