Raynaud's phenomenon is a condition where the blood vessels in participants fingers and toes get too narrow when cold or stressed. This makes participants fingers and toes change colors - they might turn white, then blue, and finally red as blood flow returns. It can be painful and cause numbness or tingling.

When participants have Raynaud's, blood vessels react too strongly to cold or stress. Fingers and toes may turn white (blood moves away from the area), blue (lack of oxygen), or red and feel painful or tingly when warming up. These episodes usually last from a few minutes to several hours.

There are two types of Raynaud's. Primary Raynaud's (also called Raynaud's disease) itself and isn't connected to other health problems. It's the most common type and affects mostly women under 30. Secondary Raynaud's (also called Raynaud's phenomenon) is caused by other diseases like lupus, scleroderma, or rheumatoid arthritis. This type tends to be more serious and may cause painful sores on fingertips called digital ulcers.

For mild cases, staying warm might be enough. But if symptoms are severe, participants doctor might prescribe various medications including calcium channel blockers - blood pressure medicines that help open blood vessels, or other vasodilators - medicines that widen blood vessels. About 40% of people with scleroderma develop painful sores on their fingertips called digital ulcers. These happen when there isn't enough blood flow to heal small injuries.

For severe cases with digital ulcers, doctors might use prostacyclin therapy - medicines that mimic a natural substance that opens blood vessels. Oral treprostinil is a newer pill form of prostacyclin therapy that helps improve blood flow. The investigators are conducting a research study testing whether oral treprostinil - a pill that mimics prostacyclin (a natural blood vessel opener) - can help people with severe Raynaud's that doesn't respond to usual treatments. This represents hope for better treatment options for people with the most challenging cases of this condition.

Inclusion Criteria:

1. Patients aged ≥ 18 years

2. Active Raynaud's Phenomenon defined as patients with refractory RP having four or more RP attacks per week in the 4 weeks before inclusion in the study.

3. Patients with either:

   1. Primary Raynaud's Phenomenon
   2. Patients with Raynaud's secondary to connective tissue diseases (including scleroderma (SSc), limited scleroderma (CREST), mixed connective tissue disease (MCTD), primary Sjogren's syndrome (SS), systemic lupus erythematosus (SLE), with diagnosis of the underlying rheumatic disease based on standard criteria.

4. If patients are on phosphodiesterase inhibitors (sildenafil, tadalafil or vardenafil), endothelin antagonists, alpha adrenergic antagonists, or calcium channel blockers, their dose must be stable, defined as 3-months with no change in dose or frequency.

5. If female of childbearing potential (FOCP), has demonstrated a negative beta HCG (human chorionic gonadotropin) serum pregnancy test, and agrees to comply with any applicable contraceptive requirements of the protocol

6. If female of non-childbearing potential, meets either of the following criteria:

   1. Is in a postmenopausal state defined as no menses for 12 months without an alternative medical cause and follicle-stimulating hormone (FSH) level consistent with postmenopause (>25 mIU/mL). If a participant is >60 years old and has been amenorrheic for >5 years, the participant may be enrolled with an FSH <25 mIU/mL after discussion with the PI.
   2. Has a documented hysterectomy, bilaterial oophorectomy, or salpingectomy.

Exclusion Criteria:

1. Uncontrolled hypertension, diabetes mellitus, acute coronary or cerebrovascular event within 3 months, history of sympathectomy
2. Smoking within 3 months or smoking cessation using nicotine products
3. History of alcohol or other substance abuse within the previous year
4. Subjects with diverticulosis confirmed via endoscopic evaluation of the sigmoid colon with at least three diverticula noted
5. Subjects with moderate to severe liver disease, Child Pugh Class B or C
6. Subjects currently taking any other prostacyclin.
7. Pregnant or breast feeding or considering pregnancy in next 4 months
8. Was dosed in any clinical research study evaluating another investigational drug (including biologics) or therapy (including specific immunotherapy) within 30 days or 5 half-lives (whichever is longer) of an investigational biologic drug before the start of the screening period.
9. Any serious chronic, and/or unstable pre-existing medical, surgical, psychiatric or other condition that could interfere with the participant's safety, obtaining informed consent, or compliance with study procedures per investigator's discretion.
10. Hospitalization for any indication within 7 days before the start of screening.