Obesity effect on the characteristics of the blood-thinning drug rivaroxaban

Rivaroxaban is the exposure drug. If the primary physician decided to start the patient on rivaroxaban, they will be screened for enrollment in this study. It will be prescribed and administered to morbidly obese patients (body weight >120 kg or BMI of 40 kg/m2 or more, and patients with BMI 30 to <35 kg/m2 ) who present with venous thromboembolisms (including deep vein thrombosis or pulmonary embolisms) or atrial fibrillation if no contraindications exist. We will draw blood samples at different time-points starting pre-dose and up to 96 hours after the first dose to measure the drug concentration at the blood and draw the area under the curve (AUC) graph for morbidly obese vs. the control group. In addition to comparing drug concentration among groups, we will also explore the difference in the pharmacodynamics of the drug as well as any genetic polymorphisms that might explain any differences. Rivaroxaban dose is 15 mg oral tablet twice daily for 21 days then 20 mg oral tablet once daily thereafter for the treatment of acute venous thromboembolism. However, patients will be recruited to this study for up to 96 hours only. The total duration of treatment will depend on the medical condition and patient comorbidities and will be decided by the primary physicians. Dose for non-valvular atrial fibrillation is 20 mg tablet orally once daily.