There are two parts of the study. In Part 1, the invesitgaotrs want to investigate whether treatment with apixaban improves pain and quality of life in patients with painful venous malformations The participants are randomized to different treatment orders of the two treatment periods with apixaban and placebo. Arm 1 starts apixaban followed by placebo and arm 2 starts with placebo followed by apixaban. Between the treatment sequences there will be a washout period of minimum one week.
The participants will register pain and use og pain medication in a diary every day for one week before start of treatment and before evaluation of effect. Also, a quality of life form will be filled out before each consultation.
In Part 2, the investigators will investigate long-term effect and safety of apixaban and reduce dose after 3 months to find the minimal effective dose.
Part 2 includes participants from Part 1 study who experienced effect of treatment or who agree to continue apixaban treatment. Study start of Part 2 is at the end of Part 1. All participants receive the same dose of apixaban as in part 1 (5 mg twice daily), and after 3 months (visit 2) the dose is reduced to 2.5 mg twice daily.
1. Participant must be 18-85 years of age at the time of signing the informed consent form (ICF).
History of major bleeding, known disease of the GI tractus with risk of bleeding (ulcera, IBD, tumor), known hemostatic disorder/hemophilia, bariatric surgery or other condition resulting in impaired adsorption of drug, active cancer
Lesion or condition if considered a significant risk factor for major bleeding. This may include current or recent gastrointestinal ulceration, presence of malignant neoplasms at high risk of bleeding, recent brain or spinal injury, recent brain, spinal or ophthalmic surgery, recent intracranial haemorrhage, known or suspected oesophageal varices, arteriovenous malformations, vascular aneurysms or major intraspinal or intracerebral vascular abnormalities
Current treatment with platelet inhibitor, any other anticoagulation treatment e.g. unfractionated heparin, low molecular weight heparin (dalteparin, enoxaparin), heparin derivates (fondaparinux), oral anticoagulants (warfarin, dabigatran, rivaroxaban, edoxaban), NSAIDs, cancer therapy with chemotherapy
Current treatment with sirolimus