Fucoidan in the Treatment of Active Rheumatoid Arthritis

Inclusion Criteria: * Patients aged 18-65 years (inclusive) at screening, regardless of gender, with a minimum weight of 35 kg. * Patients meeting the 2010 ACR classification criteria for rheumatoid arthritis. * Patients with active rheumatoid arthritis showing moderate-to-high disease activity (DAS28-ESR \>3.2) despite current treatment. * If receiving conventional NSAIDs or other pain medications, the dose must have been stable for at least 2 weeks prior to the first study drug administration and remain unchanged during the study period. * If taking oral corticosteroids, patients must have been on treatment for at least 4 weeks, with the dose stabilized at an average of ≤1.0 mg/kg/day prednisone equivalent for at least 4 weeks prior to the first study drug administration, and remain unchanged during the study period. * If receiving DMARDs (methotrexate ≤25 mg/week with folic acid supplementation \[recommended ≥5 mg/week\] or leflunomide ≤40 mg/day), patients must have been on treatment for ≥8 weeks, with the dose stable for at least 4 weeks prior to the first study drug administration, and remain unchanged during the study period. * Female patients of childbearing potential must have negative serum and urine pregnancy test results at screening. * From the time of signing the informed consent form throughout the study and for 3 months after the last dose, female patients of childbearing potential and male patients who have not undergone vasectomy must use effective contraception. * Patients must be willing and able to comply with the study restrictions. * Patients must sign the informed consent form, understand the purpose and procedures of the study, and be willing to participate in the study. Exclusion Criteria: * Patients currently receiving biologic therapy. * Patients with other inflammatory joint diseases or connective tissue diseases. * Patients with significant bone marrow impairment or significant anemia, leukopenia, or thrombocytopenia secondary to inactive rheumatoid arthritis. * Patients with persistent or severe infections within 3 months prior to enrollment. * Patients with uncontrolled hypertension, uncontrolled diabetes, unstable ischemic heart disease, active inflammatory bowel disease, active peptic ulcers, terminal illnesses, or other conditions that, in the investigator's opinion, would pose a risk to the patient's participation in the study. * Patients with clinically relevant cardiovascular, hepatic, neurological, endocrine, or other major systemic diseases that would complicate the implementation of the protocol or interpretation of study results. * Patients with severe hypoalbuminemia (serum albumin \<30 g/L), such as due to severe liver disease or nephrotic syndrome. * Patients with moderate or severe renal impairment, defined as serum creatinine \>133 μmol/L (or 1.5 mg/dL). * Patients with a recent or clinically significant history of drug or alcohol abuse. * Patients with impaired liver function or persistent alanine aminotransferase levels \>2 times the upper limit of normal. * Pregnant patients. * Breastfeeding patients. * Patients with congenital or acquired severe immunodeficiency, a history of cancer or lymphoproliferative disorders, or those who have undergone total lymphoid irradiation. * Patients with known HIV-positive status. * Patients with known positive serology for hepatitis B or hepatitis C. * Patients enrolled in any other clinical trial involving off-label use of investigational drugs or devices, or enrolled in any other type of medical research. * Patients with any active infection (including chronic or localized infections) requiring antimicrobial therapy within 28 days prior to the first study drug dose. * Patients with a body mass index (BMI) \<18.5 kg/m² or \>30 kg/m².