The objective of this clinical trial is to evaluate the efficacy and safety of platelet aggregation function - guided precision anti - platelet therapy in patients with acute cerebral infarction. The main question it aims to answer is: among the cerebral infarction patients with possible clopidogrel resistance detected by platelet aggregation function tests, what is the efficacy and safety of using ticagrelor to replace the clopidogrel treatment regimen.

Inclusion Criteria:

1. Age ≥ 18 years old.

2. Patients diagnosed with acute non-disabling ischaemic stroke or transient ischaemic attack (TIA) with moderate to high stroke risk in accordance with the WHO diagnostic criteria, defined as follows:

   • Acute non-disabling ischaemic stroke: NIHSS score ≤ 5 at enrollment;
   • TIA with moderate to high stroke risk: ABCD₂ score ≥ 4.

3. Time from symptom onset ≤ 48 hours. (Definition of symptom onset time: the interval from the last time the patient was observed in a normal state to the time of co-administration of clopidogrel 300 mg and aspirin 100 mg.)

4. MARADP ≥ 35% measured at 5-20 hours after the patient received antiplatelet therapy with co-administration of clopidogrel 300 mg and aspirin 100 mg within 48 hours of symptom onset.

5. Written informed consent signed by the patient or their legal representative.

Exclusion Criteria:

1. Imaging examinations suggestive of hemorrhagic stroke, hemorrhagic transformation, or other pathological cerebral disorders, such as vascular malformation, tumor, abscess, or other common non-ischemic cerebral diseases (e.g., multiple sclerosis).

2. Minor stroke/TIA induced by angioplasty or vascular surgery.

3. Routine electrocardiogram (ECG) suggestive of atrial fibrillation (AF), or physical examination findings of typical AF signs including completely irregular cardiac rhythm, variable intensity of the first heart sound, and pulse deficit.

4. Having definite indications for anticoagulant therapy (suspected cardiogenic embolism, e.g., atrial fibrillation, known artificial heart valve, suspected endocarditis, etc.).

5. Patients who have received intravenous thrombolysis, intra-arterial thrombolysis, mechanical thrombectomy, or any revascularization surgery after the current onset, or plan to receive such procedures within 90 days.

6. Use of antiplatelet agents other than aspirin and clopidogrel (e.g., ticagrelor, prasugrel) within 7 days.

7. History of gastrointestinal bleeding, intracranial hemorrhage, massive hemorrhage or blood transfusion in the recent period (excluding mild hemoptysis and mild abnormal vaginal bleeding), or history of other hemorrhagic diseases caused by coagulation dysfunction (e.g., purpura).

8. Having contraindications to or intolerance of clopidogrel, ticagrelor, or aspirin, including:

   • Known history of hypersensitivity;
   • Severe hepatic or renal insufficiency (definition of severe hepatic insufficiency: ALT > 2× upper limit of normal [ULN] or AST > 2× ULN; definition of severe renal insufficiency: creatinine > 1.5× ULN);
   • Severe heart failure (NYHA Class Ⅲ or Ⅳ);
   • Coagulation disorders or history of systemic hemorrhage;
   • History of previous thrombocytopenia or neutropenia;
   • History of previous drug-induced hematological diseases or hepatic dysfunction.

9. Leukopenia (< 2×10⁹/L) or thrombocytopenia (< 100×10⁹/L).

10. Use of heparin or oral anticoagulants within 10 days prior to enrollment.

11. Patients with severe cardiac, pulmonary, hepatic, or renal insufficiency, and those with severe comorbidities (e.g., malignancy, chronic airflow limitation, severe dementia, severe heart failure).

12. Women of childbearing age with a negative pregnancy test but who refuse to adopt effective contraceptive measures; pregnant or lactating women.

13. Poor compliance, unable to cooperate with the requirements of the study.