AIMS Venous thromboembolism is an important cause of postoperative morbidity and mortality in bariatric surgery. Studies of direct oral anticoagulants (DOACs) are not available in this surgical field. The objective of this phase 1 clinical trial was to investigate pharmacokinetic and pharmacodynamic (PK/PD) parameters of rivaroxaban in bariatric patients. METHODS In this single-centre study, obese patients received single oral doses of rivaroxaban (10 mg) one day before and three days after bariatric surgery. PK and PD parameters were assessed at baseline and during 24 hours after drug ingestion. RESULTS Six Roux-en-Y Gastric bypass patients (RYGB) and 6 Sleeve gastrectomy (SG) patients completed the study. Mean rivaroxaban A...