This study will test the safety of twice-daily oral dosing of combined febuxostat and inosine in 24 patients with Parkinson's disease. Participants will receive one of the four regimens, taken twice daily for 12 weeks:

Who can join: Adults with early-stage Parkinson's disease on stable medication regimens.

What participants do:

• Take their assigned dose twice daily (morning and evening) for 12 weeks.
• Visit the clinic at baseline and weeks 4, 8, and 12 for blood tests (including hypoxanthine), exams, and questionnaires.
• Keep a simple diary of any side effects or changes in daily activities.

Risks and benefits: Possible side effects include mild gastrointestinal upset, headache, or elevated uric acid levels. While direct benefit is not guaranteed, this safety data will inform future Parkinson's disease treatments.

Learn more: Contact [site-specific contact info] for details on eligibility and enrollment.

Inclusion Criteria:

1. Able to provide voluntary written informed consent.

2. Receiving stable Parkinson's disease medication (no changes in type or dose) for at least 3 months before enrollment.

3. Age 18 to 80 years at the time of consent.

4. Diagnosed with Parkinson's disease by a specialist according to MDS-PD diagnostic criteria, and at pre-enrollment screening, all of the following are met:

   1. Hoehn-Yahr stage (ON state) 1 to 3
   2. MDS-UPDRS Part III (ON state) score 10 to 35
   3. Mini-Mental State Examination (MMSE) score ≥ 24

Exclusion Criteria:

1. Requires almost total assistance in daily life and is unable to walk or stand unaided.
2. Currently taking azathioprine, mercaptopurine hydrate, vidarabine, didanosine, or rosuvastatin.
3. Used febuxostat, allopurinol, or topiroxostat within 3 months before study start.
4. Taking any supplement containing inosine.
5. Started any new Parkinson's disease medication or therapy within 3 months before enrollment.
6. Serum creatinine >1.5× upper limit of normal (ULN), or AST (GOT) or ALT (GPT) >2× ULN at screening.
7. History of surgical treatment for Parkinson's disease.
8. History of or comorbid hypersensitivity/allergy to any ingredient of the investigational drugs.
9. Participation in another clinical trial involving an unapproved drug within 30 days before consent, or currently enrolled in another interventional study.
10. Pregnant or breastfeeding, or unwilling/unable to use reliable contraception during the study period.
11. Positive test at screening for HIV, HBV, HTLV-1, or syphilis; **HCV antibody-positive with undetectable HCV RNA** is allowed.
12. Unable to take the investigational drugs orally without changing the dosage form.
13. Gastrointestinal disease or prior GI surgery that may affect drug absorption, as judged by the investigator.
14. Psychiatric disorder or symptoms that interfere with daily life and make study participation difficult.
15. Unable to complete assessments or questionnaires independently.
16. Any other condition that, in the investigator's judgment, would make participation unsafe or inappropriate.

De-identified individual participant data (including the dataset and data dictionary) and the whole study protocol will be made available to qualified researchers beginning 6 months after publication and ending 3 years after publication. Requests should be directed to the corresponding author, Dr. Hirohisa Watanabe (email: hirohisa.watanabe@fujita-hu.ac.jp), with a research proposal and data use agreement.

IPD Sharing Time Frame: Available 6 months to 3 years after publication. IPD Sharing Access Criteria: Qualified researchers with IRB/ethics approval and a signed data use agreement.

Available 6 months to 3 years after publication of the primary results.

Qualified researchers who have obtained approval from their institutional review board or ethics committee and who sign a data use agreement with the study sponsor may request access to de-identified individual participant data, the full study protocol, statistical analysis plan, informed consent form, and analytic code. Requests should be submitted via email to the corresponding author, Dr. Hirohisa Watanabe (hirohisa.watanabe@fujita-hu.ac.jp), and include a brief research proposal and evidence of IRB/ethics approval.