This is a Phase 1b, double-blind (participants and Investigators), placebo-controlled, randomized, single-ascending dose, multi-center study to assess the safety, efficacy, tolerability, pharmacokinetics (PK), and pharmacodynamics (PD) of DS-1040b in participants with acute submassive pulmonary embolism.

Inclusion Criteria:

• Male or female subjects, age 18 to 75 years admitted to hospital with a clinical diagnosis of acute pulmonary embolism (PE) categorized as low risk or intermediate-risk or submassive PE and for whom catheter-based therapy is not planned;
• Subjects must have a computed tomography angiography (CTA) scan confirming the PE diagnosis and with at least one measurable index lesion in a segmental or larger pulmonary artery prior to randomization;
• Subjects should be in otherwise satisfactory health in the opinion of the Investigator;
• Subjects must be able to provide written informed consent.

Exclusion Criteria:

• Subjects with acute PE categorized as high-risk or massive, or who are hemodynamically unstable, evidenced by a heart rate > 120 /min and a systolic blood pressure (SBP) of < 90 mmHg for more than 15 consecutive minutes or a drop in SBP of > 40 mmHg since presentation;
• Subjects for whom use of a thrombolytic, either systemic or via catheter, is planned;
• Subjects with PE lesions only in the sub-segmental or smaller arteries;
• Subjects receiving any vitamin K antagonists (VKAs) prior to randomization or receiving more than 36 hours treatment with low molecular weight (LMW) Heparin in therapeutic doses prior to randomization;
• Subjects who had a prior intracranial hemorrhage, known arteriovenous malformation or aneurysm, head trauma, or evidence of active bleeding;
• Subjects who within 48 hours of randomization have used an anti-Factor IIa agent such as dabigatran or an anti-FXa agent such as rivaroxaban, apixaban, or edoxaban;
• Subjects who within 21 days prior to randomization have had gastrointestinal or genitourinary bleeding;
• Subjects who within 14 days prior to randomization have had major surgery or a lumbar puncture (or epidural steroid injection);
• Subjects with diagnosed active liver disease or with elevation of liver enzymes/bilirubin.

De-identified individual participant data (IPD) and applicable supporting clinical trial documents may be available upon request at https://vivli.org/. In cases where clinical trial data and supporting documents are provided pursuant to our company policies and procedures, Daiichi Sankyo will continue to protect the privacy of our clinical trial participants. Details on data sharing criteria and the procedure for requesting access can be found at this web address: https://vivli.org/ourmember/daiichi-sankyo/

Studies for which the medicine and indication have received European Union (EU) and United States (US), and/or Japan (JP) marketing approval on or after 01 January 2014 or by the US or EU or JP Health Authorities when regulatory submissions in all regions are not planned and after the primary study results have been accepted for publication.

Formal request from qualified scientific and medical researchers on IPD and clinical study documents from clinical trials supporting products submitted and licensed in the United States, the European Union and/or Japan from 01 January 2014 and beyond for the purpose of conducting legitimate research. This must be consistent with the principle of safeguarding study participants' privacy and consistent with provision of informed consent.